drivers/block/loop.c | 41 ++++++++++++++++++++++++++++++----------- 1 file changed, 30 insertions(+), 11 deletions(-)
loop_set_status() is allowed to change the loop device while there
are other openers of the device, even exclusive ones.
In this case, it causes a KASAN: slab-out-of-bounds Read in
ext4_search_dir(), since when looking for an entry in an inlined
directory, e_value_offs is changed underneath the filesystem by
loop_set_status().
Fix the problem by forbidding loop_set_status() from modifying the loop
device while there are exclusive openers of the device. This is similar
to the fix in loop_configure() by commit 33ec3e53e7b1 ("loop: Don't
change loop device under exclusive opener") alongside commit ecbe6bc0003b
("block: use bd_prepare_to_claim directly in the loop driver").
Reported-by: syzbot+3ee481e21fd75e14c397@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=3ee481e21fd75e14c397
Tested-by: syzbot+3ee481e21fd75e14c397@syzkaller.appspotmail.com
Signed-off-by: Raphael Pinsonneault-Thibeault <rpthibeault@gmail.com>
---
ML thread for previous, misguided patch idea:
https://lore.kernel.org/all/20251112185712.2031993-2-rpthibeault@gmail.com/t/
drivers/block/loop.c | 41 ++++++++++++++++++++++++++++++-----------
1 file changed, 30 insertions(+), 11 deletions(-)
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 053a086d547e..756ee682e767 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1222,13 +1222,24 @@ static int loop_clr_fd(struct loop_device *lo)
}
static int
-loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
+loop_set_status(struct loop_device *lo, blk_mode_t mode,
+ struct block_device *bdev, const struct loop_info64 *info)
{
int err;
bool partscan = false;
bool size_changed = false;
unsigned int memflags;
+ /*
+ * If we don't hold exclusive handle for the device, upgrade to it
+ * here to avoid changing device under exclusive owner.
+ */
+ if (!(mode & BLK_OPEN_EXCL)) {
+ err = bd_prepare_to_claim(bdev, loop_set_status, NULL);
+ if (err)
+ goto out_reread_partitions;
+ }
+
err = mutex_lock_killable(&lo->lo_mutex);
if (err)
return err;
@@ -1270,6 +1281,9 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
}
out_unlock:
mutex_unlock(&lo->lo_mutex);
+ if (!(mode & BLK_OPEN_EXCL))
+ bd_abort_claiming(bdev, loop_set_status);
+out_reread_partitions:
if (partscan)
loop_reread_partitions(lo);
@@ -1349,7 +1363,9 @@ loop_info64_to_old(const struct loop_info64 *info64, struct loop_info *info)
}
static int
-loop_set_status_old(struct loop_device *lo, const struct loop_info __user *arg)
+loop_set_status_old(struct loop_device *lo, blk_mode_t mode,
+ struct block_device *bdev,
+ const struct loop_info __user *arg)
{
struct loop_info info;
struct loop_info64 info64;
@@ -1357,17 +1373,19 @@ loop_set_status_old(struct loop_device *lo, const struct loop_info __user *arg)
if (copy_from_user(&info, arg, sizeof (struct loop_info)))
return -EFAULT;
loop_info64_from_old(&info, &info64);
- return loop_set_status(lo, &info64);
+ return loop_set_status(lo, mode, bdev, &info64);
}
static int
-loop_set_status64(struct loop_device *lo, const struct loop_info64 __user *arg)
+loop_set_status64(struct loop_device *lo, blk_mode_t mode,
+ struct block_device *bdev,
+ const struct loop_info64 __user *arg)
{
struct loop_info64 info64;
if (copy_from_user(&info64, arg, sizeof (struct loop_info64)))
return -EFAULT;
- return loop_set_status(lo, &info64);
+ return loop_set_status(lo, mode, bdev, &info64);
}
static int
@@ -1546,14 +1564,14 @@ static int lo_ioctl(struct block_device *bdev, blk_mode_t mode,
case LOOP_SET_STATUS:
err = -EPERM;
if ((mode & BLK_OPEN_WRITE) || capable(CAP_SYS_ADMIN))
- err = loop_set_status_old(lo, argp);
+ err = loop_set_status_old(lo, mode, bdev, argp);
break;
case LOOP_GET_STATUS:
return loop_get_status_old(lo, argp);
case LOOP_SET_STATUS64:
err = -EPERM;
if ((mode & BLK_OPEN_WRITE) || capable(CAP_SYS_ADMIN))
- err = loop_set_status64(lo, argp);
+ err = loop_set_status64(lo, mode, bdev, argp);
break;
case LOOP_GET_STATUS64:
return loop_get_status64(lo, argp);
@@ -1647,8 +1665,9 @@ loop_info64_to_compat(const struct loop_info64 *info64,
}
static int
-loop_set_status_compat(struct loop_device *lo,
- const struct compat_loop_info __user *arg)
+loop_set_status_compat(struct loop_device *lo, blk_mode_t mode,
+ struct block_device *bdev,
+ const struct compat_loop_info __user *arg)
{
struct loop_info64 info64;
int ret;
@@ -1656,7 +1675,7 @@ loop_set_status_compat(struct loop_device *lo,
ret = loop_info64_from_compat(arg, &info64);
if (ret < 0)
return ret;
- return loop_set_status(lo, &info64);
+ return loop_set_status(lo, mode, bdev, &info64);
}
static int
@@ -1682,7 +1701,7 @@ static int lo_compat_ioctl(struct block_device *bdev, blk_mode_t mode,
switch(cmd) {
case LOOP_SET_STATUS:
- err = loop_set_status_compat(lo,
+ err = loop_set_status_compat(lo, mode, bdev,
(const struct compat_loop_info __user *)arg);
break;
case LOOP_GET_STATUS:
--
2.43.0On Fri 14-11-25 09:42:05, Raphael Pinsonneault-Thibeault wrote:
> loop_set_status() is allowed to change the loop device while there
> are other openers of the device, even exclusive ones.
>
> In this case, it causes a KASAN: slab-out-of-bounds Read in
> ext4_search_dir(), since when looking for an entry in an inlined
> directory, e_value_offs is changed underneath the filesystem by
> loop_set_status().
>
> Fix the problem by forbidding loop_set_status() from modifying the loop
> device while there are exclusive openers of the device. This is similar
> to the fix in loop_configure() by commit 33ec3e53e7b1 ("loop: Don't
> change loop device under exclusive opener") alongside commit ecbe6bc0003b
> ("block: use bd_prepare_to_claim directly in the loop driver").
>
> Reported-by: syzbot+3ee481e21fd75e14c397@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=3ee481e21fd75e14c397
> Tested-by: syzbot+3ee481e21fd75e14c397@syzkaller.appspotmail.com
> Signed-off-by: Raphael Pinsonneault-Thibeault <rpthibeault@gmail.com>
This patch looks mostly good to me. Just one comment:
> -loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
> +loop_set_status(struct loop_device *lo, blk_mode_t mode,
> + struct block_device *bdev, const struct loop_info64 *info)
> {
> int err;
> bool partscan = false;
> bool size_changed = false;
> unsigned int memflags;
>
> + /*
> + * If we don't hold exclusive handle for the device, upgrade to it
> + * here to avoid changing device under exclusive owner.
> + */
> + if (!(mode & BLK_OPEN_EXCL)) {
> + err = bd_prepare_to_claim(bdev, loop_set_status, NULL);
> + if (err)
> + goto out_reread_partitions;
> + }
> +
So now any LOOP_SET_STATUS call will fail for device that is already
exclusively open. There are some operations (like modifying the AUTOCLEAR
flag or loop device name) that are safe even for a device with a mounted
filesystem. I wouldn't probably bother with that now but I wanted to note
that there may be valid uses of LOOP_SET_STATUS even for an exclusively
open loop device and if there are users of that out there we might need to
refine this a bit. Anyway for now feel free to add:
Reviewed-by: Jan Kara <jack@suse.cz>
Honza
> err = mutex_lock_killable(&lo->lo_mutex);
> if (err)
> return err;
> @@ -1270,6 +1281,9 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
> }
> out_unlock:
> mutex_unlock(&lo->lo_mutex);
> + if (!(mode & BLK_OPEN_EXCL))
> + bd_abort_claiming(bdev, loop_set_status);
> +out_reread_partitions:
> if (partscan)
> loop_reread_partitions(lo);
>
> @@ -1349,7 +1363,9 @@ loop_info64_to_old(const struct loop_info64 *info64, struct loop_info *info)
> }
>
> static int
> -loop_set_status_old(struct loop_device *lo, const struct loop_info __user *arg)
> +loop_set_status_old(struct loop_device *lo, blk_mode_t mode,
> + struct block_device *bdev,
> + const struct loop_info __user *arg)
> {
> struct loop_info info;
> struct loop_info64 info64;
> @@ -1357,17 +1373,19 @@ loop_set_status_old(struct loop_device *lo, const struct loop_info __user *arg)
> if (copy_from_user(&info, arg, sizeof (struct loop_info)))
> return -EFAULT;
> loop_info64_from_old(&info, &info64);
> - return loop_set_status(lo, &info64);
> + return loop_set_status(lo, mode, bdev, &info64);
> }
>
> static int
> -loop_set_status64(struct loop_device *lo, const struct loop_info64 __user *arg)
> +loop_set_status64(struct loop_device *lo, blk_mode_t mode,
> + struct block_device *bdev,
> + const struct loop_info64 __user *arg)
> {
> struct loop_info64 info64;
>
> if (copy_from_user(&info64, arg, sizeof (struct loop_info64)))
> return -EFAULT;
> - return loop_set_status(lo, &info64);
> + return loop_set_status(lo, mode, bdev, &info64);
> }
>
> static int
> @@ -1546,14 +1564,14 @@ static int lo_ioctl(struct block_device *bdev, blk_mode_t mode,
> case LOOP_SET_STATUS:
> err = -EPERM;
> if ((mode & BLK_OPEN_WRITE) || capable(CAP_SYS_ADMIN))
> - err = loop_set_status_old(lo, argp);
> + err = loop_set_status_old(lo, mode, bdev, argp);
> break;
> case LOOP_GET_STATUS:
> return loop_get_status_old(lo, argp);
> case LOOP_SET_STATUS64:
> err = -EPERM;
> if ((mode & BLK_OPEN_WRITE) || capable(CAP_SYS_ADMIN))
> - err = loop_set_status64(lo, argp);
> + err = loop_set_status64(lo, mode, bdev, argp);
> break;
> case LOOP_GET_STATUS64:
> return loop_get_status64(lo, argp);
> @@ -1647,8 +1665,9 @@ loop_info64_to_compat(const struct loop_info64 *info64,
> }
>
> static int
> -loop_set_status_compat(struct loop_device *lo,
> - const struct compat_loop_info __user *arg)
> +loop_set_status_compat(struct loop_device *lo, blk_mode_t mode,
> + struct block_device *bdev,
> + const struct compat_loop_info __user *arg)
> {
> struct loop_info64 info64;
> int ret;
> @@ -1656,7 +1675,7 @@ loop_set_status_compat(struct loop_device *lo,
> ret = loop_info64_from_compat(arg, &info64);
> if (ret < 0)
> return ret;
> - return loop_set_status(lo, &info64);
> + return loop_set_status(lo, mode, bdev, &info64);
> }
>
> static int
> @@ -1682,7 +1701,7 @@ static int lo_compat_ioctl(struct block_device *bdev, blk_mode_t mode,
>
> switch(cmd) {
> case LOOP_SET_STATUS:
> - err = loop_set_status_compat(lo,
> + err = loop_set_status_compat(lo, mode, bdev,
> (const struct compat_loop_info __user *)arg);
> break;
> case LOOP_GET_STATUS:
> --
> 2.43.0
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
On Tue 02-12-25 11:07:06, Jan Kara wrote:
> On Fri 14-11-25 09:42:05, Raphael Pinsonneault-Thibeault wrote:
> > loop_set_status() is allowed to change the loop device while there
> > are other openers of the device, even exclusive ones.
> >
> > In this case, it causes a KASAN: slab-out-of-bounds Read in
> > ext4_search_dir(), since when looking for an entry in an inlined
> > directory, e_value_offs is changed underneath the filesystem by
> > loop_set_status().
> >
> > Fix the problem by forbidding loop_set_status() from modifying the loop
> > device while there are exclusive openers of the device. This is similar
> > to the fix in loop_configure() by commit 33ec3e53e7b1 ("loop: Don't
> > change loop device under exclusive opener") alongside commit ecbe6bc0003b
> > ("block: use bd_prepare_to_claim directly in the loop driver").
> >
> > Reported-by: syzbot+3ee481e21fd75e14c397@syzkaller.appspotmail.com
> > Closes: https://syzkaller.appspot.com/bug?extid=3ee481e21fd75e14c397
> > Tested-by: syzbot+3ee481e21fd75e14c397@syzkaller.appspotmail.com
> > Signed-off-by: Raphael Pinsonneault-Thibeault <rpthibeault@gmail.com>
>
> This patch looks mostly good to me. Just one comment:
>
> > -loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
> > +loop_set_status(struct loop_device *lo, blk_mode_t mode,
> > + struct block_device *bdev, const struct loop_info64 *info)
> > {
> > int err;
> > bool partscan = false;
> > bool size_changed = false;
> > unsigned int memflags;
> >
> > + /*
> > + * If we don't hold exclusive handle for the device, upgrade to it
> > + * here to avoid changing device under exclusive owner.
> > + */
> > + if (!(mode & BLK_OPEN_EXCL)) {
> > + err = bd_prepare_to_claim(bdev, loop_set_status, NULL);
> > + if (err)
> > + goto out_reread_partitions;
> > + }
> > +
>
> So now any LOOP_SET_STATUS call will fail for device that is already
> exclusively open. There are some operations (like modifying the AUTOCLEAR
> flag or loop device name) that are safe even for a device with a mounted
> filesystem. I wouldn't probably bother with that now but I wanted to note
> that there may be valid uses of LOOP_SET_STATUS even for an exclusively
> open loop device and if there are users of that out there we might need to
> refine this a bit. Anyway for now feel free to add:
>
> Reviewed-by: Jan Kara <jack@suse.cz>
Raphael, this patch seems to have fallen through the cracks. Can you please
resend it to Jens with by Reviewed-by tag so that he picks it up? Thanks!
Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
loop_set_status() is allowed to change the loop device while there
are other openers of the device, even exclusive ones.
In this case, it causes a KASAN: slab-out-of-bounds Read in
ext4_search_dir(), since when looking for an entry in an inlined
directory, e_value_offs is changed underneath the filesystem by
loop_set_status().
Fix the problem by forbidding loop_set_status() from modifying the loop
device while there are exclusive openers of the device. This is similar
to the fix in loop_configure() by commit 33ec3e53e7b1 ("loop: Don't
change loop device under exclusive opener") alongside commit ecbe6bc0003b
("block: use bd_prepare_to_claim directly in the loop driver").
Reported-by: syzbot+3ee481e21fd75e14c397@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=3ee481e21fd75e14c397
Tested-by: syzbot+3ee481e21fd75e14c397@syzkaller.appspotmail.com
Tested-by: Yongpeng Yang <yangyongpeng@xiaomi.com>
Signed-off-by: Raphael Pinsonneault-Thibeault <rpthibeault@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
---
v2:
- added Tested-by and Reviewed-by tags for v1
drivers/block/loop.c | 41 ++++++++++++++++++++++++++++++-----------
1 file changed, 30 insertions(+), 11 deletions(-)
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 053a086d547e..756ee682e767 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1222,13 +1222,24 @@ static int loop_clr_fd(struct loop_device *lo)
}
static int
-loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
+loop_set_status(struct loop_device *lo, blk_mode_t mode,
+ struct block_device *bdev, const struct loop_info64 *info)
{
int err;
bool partscan = false;
bool size_changed = false;
unsigned int memflags;
+ /*
+ * If we don't hold exclusive handle for the device, upgrade to it
+ * here to avoid changing device under exclusive owner.
+ */
+ if (!(mode & BLK_OPEN_EXCL)) {
+ err = bd_prepare_to_claim(bdev, loop_set_status, NULL);
+ if (err)
+ goto out_reread_partitions;
+ }
+
err = mutex_lock_killable(&lo->lo_mutex);
if (err)
return err;
@@ -1270,6 +1281,9 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
}
out_unlock:
mutex_unlock(&lo->lo_mutex);
+ if (!(mode & BLK_OPEN_EXCL))
+ bd_abort_claiming(bdev, loop_set_status);
+out_reread_partitions:
if (partscan)
loop_reread_partitions(lo);
@@ -1349,7 +1363,9 @@ loop_info64_to_old(const struct loop_info64 *info64, struct loop_info *info)
}
static int
-loop_set_status_old(struct loop_device *lo, const struct loop_info __user *arg)
+loop_set_status_old(struct loop_device *lo, blk_mode_t mode,
+ struct block_device *bdev,
+ const struct loop_info __user *arg)
{
struct loop_info info;
struct loop_info64 info64;
@@ -1357,17 +1373,19 @@ loop_set_status_old(struct loop_device *lo, const struct loop_info __user *arg)
if (copy_from_user(&info, arg, sizeof (struct loop_info)))
return -EFAULT;
loop_info64_from_old(&info, &info64);
- return loop_set_status(lo, &info64);
+ return loop_set_status(lo, mode, bdev, &info64);
}
static int
-loop_set_status64(struct loop_device *lo, const struct loop_info64 __user *arg)
+loop_set_status64(struct loop_device *lo, blk_mode_t mode,
+ struct block_device *bdev,
+ const struct loop_info64 __user *arg)
{
struct loop_info64 info64;
if (copy_from_user(&info64, arg, sizeof (struct loop_info64)))
return -EFAULT;
- return loop_set_status(lo, &info64);
+ return loop_set_status(lo, mode, bdev, &info64);
}
static int
@@ -1546,14 +1564,14 @@ static int lo_ioctl(struct block_device *bdev, blk_mode_t mode,
case LOOP_SET_STATUS:
err = -EPERM;
if ((mode & BLK_OPEN_WRITE) || capable(CAP_SYS_ADMIN))
- err = loop_set_status_old(lo, argp);
+ err = loop_set_status_old(lo, mode, bdev, argp);
break;
case LOOP_GET_STATUS:
return loop_get_status_old(lo, argp);
case LOOP_SET_STATUS64:
err = -EPERM;
if ((mode & BLK_OPEN_WRITE) || capable(CAP_SYS_ADMIN))
- err = loop_set_status64(lo, argp);
+ err = loop_set_status64(lo, mode, bdev, argp);
break;
case LOOP_GET_STATUS64:
return loop_get_status64(lo, argp);
@@ -1647,8 +1665,9 @@ loop_info64_to_compat(const struct loop_info64 *info64,
}
static int
-loop_set_status_compat(struct loop_device *lo,
- const struct compat_loop_info __user *arg)
+loop_set_status_compat(struct loop_device *lo, blk_mode_t mode,
+ struct block_device *bdev,
+ const struct compat_loop_info __user *arg)
{
struct loop_info64 info64;
int ret;
@@ -1656,7 +1675,7 @@ loop_set_status_compat(struct loop_device *lo,
ret = loop_info64_from_compat(arg, &info64);
if (ret < 0)
return ret;
- return loop_set_status(lo, &info64);
+ return loop_set_status(lo, mode, bdev, &info64);
}
static int
@@ -1682,7 +1701,7 @@ static int lo_compat_ioctl(struct block_device *bdev, blk_mode_t mode,
switch(cmd) {
case LOOP_SET_STATUS:
- err = loop_set_status_compat(lo,
+ err = loop_set_status_compat(lo, mode, bdev,
(const struct compat_loop_info __user *)arg);
break;
case LOOP_GET_STATUS:
--
2.43.0
On Wed, 17 Dec 2025 14:00:40 -0500, Raphael Pinsonneault-Thibeault wrote:
> loop_set_status() is allowed to change the loop device while there
> are other openers of the device, even exclusive ones.
>
> In this case, it causes a KASAN: slab-out-of-bounds Read in
> ext4_search_dir(), since when looking for an entry in an inlined
> directory, e_value_offs is changed underneath the filesystem by
> loop_set_status().
>
> [...]
Applied, thanks!
[1/1] loop: don't change loop device under exclusive opener in loop_set_status
commit: 08e136ebd193eae7d5eff4c66d576c4a2dabdc3f
Best regards,
--
Jens Axboe
On Wed 17-12-25 14:00:40, Raphael Pinsonneault-Thibeault wrote:
> loop_set_status() is allowed to change the loop device while there
> are other openers of the device, even exclusive ones.
>
> In this case, it causes a KASAN: slab-out-of-bounds Read in
> ext4_search_dir(), since when looking for an entry in an inlined
> directory, e_value_offs is changed underneath the filesystem by
> loop_set_status().
>
> Fix the problem by forbidding loop_set_status() from modifying the loop
> device while there are exclusive openers of the device. This is similar
> to the fix in loop_configure() by commit 33ec3e53e7b1 ("loop: Don't
> change loop device under exclusive opener") alongside commit ecbe6bc0003b
> ("block: use bd_prepare_to_claim directly in the loop driver").
>
> Reported-by: syzbot+3ee481e21fd75e14c397@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=3ee481e21fd75e14c397
> Tested-by: syzbot+3ee481e21fd75e14c397@syzkaller.appspotmail.com
> Tested-by: Yongpeng Yang <yangyongpeng@xiaomi.com>
> Signed-off-by: Raphael Pinsonneault-Thibeault <rpthibeault@gmail.com>
> Reviewed-by: Jan Kara <jack@suse.cz>
Jens, ping?
Honza
> ---
> v2:
> - added Tested-by and Reviewed-by tags for v1
>
> drivers/block/loop.c | 41 ++++++++++++++++++++++++++++++-----------
> 1 file changed, 30 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index 053a086d547e..756ee682e767 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -1222,13 +1222,24 @@ static int loop_clr_fd(struct loop_device *lo)
> }
>
> static int
> -loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
> +loop_set_status(struct loop_device *lo, blk_mode_t mode,
> + struct block_device *bdev, const struct loop_info64 *info)
> {
> int err;
> bool partscan = false;
> bool size_changed = false;
> unsigned int memflags;
>
> + /*
> + * If we don't hold exclusive handle for the device, upgrade to it
> + * here to avoid changing device under exclusive owner.
> + */
> + if (!(mode & BLK_OPEN_EXCL)) {
> + err = bd_prepare_to_claim(bdev, loop_set_status, NULL);
> + if (err)
> + goto out_reread_partitions;
> + }
> +
> err = mutex_lock_killable(&lo->lo_mutex);
> if (err)
> return err;
> @@ -1270,6 +1281,9 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
> }
> out_unlock:
> mutex_unlock(&lo->lo_mutex);
> + if (!(mode & BLK_OPEN_EXCL))
> + bd_abort_claiming(bdev, loop_set_status);
> +out_reread_partitions:
> if (partscan)
> loop_reread_partitions(lo);
>
> @@ -1349,7 +1363,9 @@ loop_info64_to_old(const struct loop_info64 *info64, struct loop_info *info)
> }
>
> static int
> -loop_set_status_old(struct loop_device *lo, const struct loop_info __user *arg)
> +loop_set_status_old(struct loop_device *lo, blk_mode_t mode,
> + struct block_device *bdev,
> + const struct loop_info __user *arg)
> {
> struct loop_info info;
> struct loop_info64 info64;
> @@ -1357,17 +1373,19 @@ loop_set_status_old(struct loop_device *lo, const struct loop_info __user *arg)
> if (copy_from_user(&info, arg, sizeof (struct loop_info)))
> return -EFAULT;
> loop_info64_from_old(&info, &info64);
> - return loop_set_status(lo, &info64);
> + return loop_set_status(lo, mode, bdev, &info64);
> }
>
> static int
> -loop_set_status64(struct loop_device *lo, const struct loop_info64 __user *arg)
> +loop_set_status64(struct loop_device *lo, blk_mode_t mode,
> + struct block_device *bdev,
> + const struct loop_info64 __user *arg)
> {
> struct loop_info64 info64;
>
> if (copy_from_user(&info64, arg, sizeof (struct loop_info64)))
> return -EFAULT;
> - return loop_set_status(lo, &info64);
> + return loop_set_status(lo, mode, bdev, &info64);
> }
>
> static int
> @@ -1546,14 +1564,14 @@ static int lo_ioctl(struct block_device *bdev, blk_mode_t mode,
> case LOOP_SET_STATUS:
> err = -EPERM;
> if ((mode & BLK_OPEN_WRITE) || capable(CAP_SYS_ADMIN))
> - err = loop_set_status_old(lo, argp);
> + err = loop_set_status_old(lo, mode, bdev, argp);
> break;
> case LOOP_GET_STATUS:
> return loop_get_status_old(lo, argp);
> case LOOP_SET_STATUS64:
> err = -EPERM;
> if ((mode & BLK_OPEN_WRITE) || capable(CAP_SYS_ADMIN))
> - err = loop_set_status64(lo, argp);
> + err = loop_set_status64(lo, mode, bdev, argp);
> break;
> case LOOP_GET_STATUS64:
> return loop_get_status64(lo, argp);
> @@ -1647,8 +1665,9 @@ loop_info64_to_compat(const struct loop_info64 *info64,
> }
>
> static int
> -loop_set_status_compat(struct loop_device *lo,
> - const struct compat_loop_info __user *arg)
> +loop_set_status_compat(struct loop_device *lo, blk_mode_t mode,
> + struct block_device *bdev,
> + const struct compat_loop_info __user *arg)
> {
> struct loop_info64 info64;
> int ret;
> @@ -1656,7 +1675,7 @@ loop_set_status_compat(struct loop_device *lo,
> ret = loop_info64_from_compat(arg, &info64);
> if (ret < 0)
> return ret;
> - return loop_set_status(lo, &info64);
> + return loop_set_status(lo, mode, bdev, &info64);
> }
>
> static int
> @@ -1682,7 +1701,7 @@ static int lo_compat_ioctl(struct block_device *bdev, blk_mode_t mode,
>
> switch(cmd) {
> case LOOP_SET_STATUS:
> - err = loop_set_status_compat(lo,
> + err = loop_set_status_compat(lo, mode, bdev,
> (const struct compat_loop_info __user *)arg);
> break;
> case LOOP_GET_STATUS:
> --
> 2.43.0
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
On 1/6/26 5:08 AM, Jan Kara wrote:
> On Wed 17-12-25 14:00:40, Raphael Pinsonneault-Thibeault wrote:
>> loop_set_status() is allowed to change the loop device while there
>> are other openers of the device, even exclusive ones.
>>
>> In this case, it causes a KASAN: slab-out-of-bounds Read in
>> ext4_search_dir(), since when looking for an entry in an inlined
>> directory, e_value_offs is changed underneath the filesystem by
>> loop_set_status().
>>
>> Fix the problem by forbidding loop_set_status() from modifying the loop
>> device while there are exclusive openers of the device. This is similar
>> to the fix in loop_configure() by commit 33ec3e53e7b1 ("loop: Don't
>> change loop device under exclusive opener") alongside commit ecbe6bc0003b
>> ("block: use bd_prepare_to_claim directly in the loop driver").
>>
>> Reported-by: syzbot+3ee481e21fd75e14c397@syzkaller.appspotmail.com
>> Closes: https://syzkaller.appspot.com/bug?extid=3ee481e21fd75e14c397
>> Tested-by: syzbot+3ee481e21fd75e14c397@syzkaller.appspotmail.com
>> Tested-by: Yongpeng Yang <yangyongpeng@xiaomi.com>
>> Signed-off-by: Raphael Pinsonneault-Thibeault <rpthibeault@gmail.com>
>> Reviewed-by: Jan Kara <jack@suse.cz>
>
> Jens, ping?
Now applied. Heads up in general, don't nest v2 or later inside the
original thread. It just makes emails get lost, as it appears part
of the original discussion.
--
Jens Axboe
On 11/14/25 22:42, Raphael Pinsonneault-Thibeault wrote:
> loop_set_status() is allowed to change the loop device while there
> are other openers of the device, even exclusive ones.
>
> In this case, it causes a KASAN: slab-out-of-bounds Read in
> ext4_search_dir(), since when looking for an entry in an inlined
> directory, e_value_offs is changed underneath the filesystem by
> loop_set_status().
>
> Fix the problem by forbidding loop_set_status() from modifying the loop
> device while there are exclusive openers of the device. This is similar
> to the fix in loop_configure() by commit 33ec3e53e7b1 ("loop: Don't
> change loop device under exclusive opener") alongside commit ecbe6bc0003b
> ("block: use bd_prepare_to_claim directly in the loop driver").
>
> Reported-by: syzbot+3ee481e21fd75e14c397@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=3ee481e21fd75e14c397
> Tested-by: syzbot+3ee481e21fd75e14c397@syzkaller.appspotmail.com
> Signed-off-by: Raphael Pinsonneault-Thibeault <rpthibeault@gmail.com>
> ---
> ML thread for previous, misguided patch idea:
> https://lore.kernel.org/all/20251112185712.2031993-2-rpthibeault@gmail.com/t/
>
> drivers/block/loop.c | 41 ++++++++++++++++++++++++++++++-----------
> 1 file changed, 30 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index 053a086d547e..756ee682e767 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -1222,13 +1222,24 @@ static int loop_clr_fd(struct loop_device *lo)
> }
>
> static int
> -loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
> +loop_set_status(struct loop_device *lo, blk_mode_t mode,
> + struct block_device *bdev, const struct loop_info64 *info)
> {
> int err;
> bool partscan = false;
> bool size_changed = false;
> unsigned int memflags;
>
> + /*
> + * If we don't hold exclusive handle for the device, upgrade to it
> + * here to avoid changing device under exclusive owner.
> + */
> + if (!(mode & BLK_OPEN_EXCL)) {
> + err = bd_prepare_to_claim(bdev, loop_set_status, NULL);
> + if (err)
> + goto out_reread_partitions;
> + }
> +
+ if (mode & BLK_OPEN_EXCL) {
+ struct block_device *whole = bdev_whole(bdev);
+
+ BUG_ON(whole->bd_claiming == NULL);
+ }
I add the above code and do the following test:
# losetup -f data.1g
# echo "0 `blockdev --getsz /dev/loop0` linear /dev/loop0 0" | dmsetup
create my-linear
# ./ioctl-test /dev/mapper/my-linear // trigger BUG_ON, ioctl-test.c is
in attachment.
The root causes of BUG_ON:
1. When creating 'my-linear' device, the mode for opening /dev/loop0
does not include the BLK_OPEN_EXCL flag.
table_load
- dm_table_create // get_mode() never assign BLK_OPEN_EXCL to {struct
dm_table *t}->mode
- populate_table
- dm_table_add_target
- linear_ctr
- dm_get_device // mode = {struct dm_table *t}->mode, never open
loop0 with BLK_OPEN_EXCL mode.
2. When 'my-linear' device is opened with the O_EXCL flag, and an ioctl
is issued to it. The dm_blk_ioctl function calls bdev->bd_disk->fops-
> ioctl(bdev, mode, cmd, arg), which passes the mode with BLK_OPEN_EXCL
flag to lo_ioctl.
3. loop0 was not opened by dm_get_device() in BLK_OPEN_EXCL mode. As a
result, whole->bd_claiming is NULL.
Thus, the BLK_OPEN_EXCL flag in the mode passed to lo_ioctl doesn't
guarantee the loop device was opened with BLK_OPEN_EXCL.
How about use per-device rw_semaphore instead of 'bd_prepare_to_claim/
bd_abort_claiming'?
Yongpeng,
> err = mutex_lock_killable(&lo->lo_mutex);
> if (err)
> return err;
> @@ -1270,6 +1281,9 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
> }
> out_unlock:
> mutex_unlock(&lo->lo_mutex);
> + if (!(mode & BLK_OPEN_EXCL))
> + bd_abort_claiming(bdev, loop_set_status);
> +out_reread_partitions:
> if (partscan)
> loop_reread_partitions(lo);
>
> @@ -1349,7 +1363,9 @@ loop_info64_to_old(const struct loop_info64 *info64, struct loop_info *info)
> }
>
> static int
> -loop_set_status_old(struct loop_device *lo, const struct loop_info __user *arg)
> +loop_set_status_old(struct loop_device *lo, blk_mode_t mode,
> + struct block_device *bdev,
> + const struct loop_info __user *arg)
> {
> struct loop_info info;
> struct loop_info64 info64;
> @@ -1357,17 +1373,19 @@ loop_set_status_old(struct loop_device *lo, const struct loop_info __user *arg)
> if (copy_from_user(&info, arg, sizeof (struct loop_info)))
> return -EFAULT;
> loop_info64_from_old(&info, &info64);
> - return loop_set_status(lo, &info64);
> + return loop_set_status(lo, mode, bdev, &info64);
> }
>
> static int
> -loop_set_status64(struct loop_device *lo, const struct loop_info64 __user *arg)
> +loop_set_status64(struct loop_device *lo, blk_mode_t mode,
> + struct block_device *bdev,
> + const struct loop_info64 __user *arg)
> {
> struct loop_info64 info64;
>
> if (copy_from_user(&info64, arg, sizeof (struct loop_info64)))
> return -EFAULT;
> - return loop_set_status(lo, &info64);
> + return loop_set_status(lo, mode, bdev, &info64);
> }
>
> static int
> @@ -1546,14 +1564,14 @@ static int lo_ioctl(struct block_device *bdev, blk_mode_t mode,
> case LOOP_SET_STATUS:
> err = -EPERM;
> if ((mode & BLK_OPEN_WRITE) || capable(CAP_SYS_ADMIN))
> - err = loop_set_status_old(lo, argp);
> + err = loop_set_status_old(lo, mode, bdev, argp);
> break;
> case LOOP_GET_STATUS:
> return loop_get_status_old(lo, argp);
> case LOOP_SET_STATUS64:
> err = -EPERM;
> if ((mode & BLK_OPEN_WRITE) || capable(CAP_SYS_ADMIN))
> - err = loop_set_status64(lo, argp);
> + err = loop_set_status64(lo, mode, bdev, argp);
> break;
> case LOOP_GET_STATUS64:
> return loop_get_status64(lo, argp);
> @@ -1647,8 +1665,9 @@ loop_info64_to_compat(const struct loop_info64 *info64,
> }
>
> static int
> -loop_set_status_compat(struct loop_device *lo,
> - const struct compat_loop_info __user *arg)
> +loop_set_status_compat(struct loop_device *lo, blk_mode_t mode,
> + struct block_device *bdev,
> + const struct compat_loop_info __user *arg)
> {
> struct loop_info64 info64;
> int ret;
> @@ -1656,7 +1675,7 @@ loop_set_status_compat(struct loop_device *lo,
> ret = loop_info64_from_compat(arg, &info64);
> if (ret < 0)
> return ret;
> - return loop_set_status(lo, &info64);
> + return loop_set_status(lo, mode, bdev, &info64);
> }
>
> static int
> @@ -1682,7 +1701,7 @@ static int lo_compat_ioctl(struct block_device *bdev, blk_mode_t mode,
>
> switch(cmd) {
> case LOOP_SET_STATUS:
> - err = loop_set_status_compat(lo,
> + err = loop_set_status_compat(lo, mode, bdev,
> (const struct compat_loop_info __user *)arg);
> break;
> case LOOP_GET_STATUS:
On Tue 18-11-25 15:10:20, Yongpeng Yang wrote:
> On 11/14/25 22:42, Raphael Pinsonneault-Thibeault wrote:
> > loop_set_status() is allowed to change the loop device while there
> > are other openers of the device, even exclusive ones.
> >
> > In this case, it causes a KASAN: slab-out-of-bounds Read in
> > ext4_search_dir(), since when looking for an entry in an inlined
> > directory, e_value_offs is changed underneath the filesystem by
> > loop_set_status().
> >
> > Fix the problem by forbidding loop_set_status() from modifying the loop
> > device while there are exclusive openers of the device. This is similar
> > to the fix in loop_configure() by commit 33ec3e53e7b1 ("loop: Don't
> > change loop device under exclusive opener") alongside commit ecbe6bc0003b
> > ("block: use bd_prepare_to_claim directly in the loop driver").
> >
> > Reported-by: syzbot+3ee481e21fd75e14c397@syzkaller.appspotmail.com
> > Closes: https://syzkaller.appspot.com/bug?extid=3ee481e21fd75e14c397
> > Tested-by: syzbot+3ee481e21fd75e14c397@syzkaller.appspotmail.com
> > Signed-off-by: Raphael Pinsonneault-Thibeault <rpthibeault@gmail.com>
> > ---
> > ML thread for previous, misguided patch idea:
> > https://lore.kernel.org/all/20251112185712.2031993-2-rpthibeault@gmail.com/t/
> >
> > drivers/block/loop.c | 41 ++++++++++++++++++++++++++++++-----------
> > 1 file changed, 30 insertions(+), 11 deletions(-)
> >
> > diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> > index 053a086d547e..756ee682e767 100644
> > --- a/drivers/block/loop.c
> > +++ b/drivers/block/loop.c
> > @@ -1222,13 +1222,24 @@ static int loop_clr_fd(struct loop_device *lo)
> > }
> > static int
> > -loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
> > +loop_set_status(struct loop_device *lo, blk_mode_t mode,
> > + struct block_device *bdev, const struct loop_info64 *info)
> > {
> > int err;
> > bool partscan = false;
> > bool size_changed = false;
> > unsigned int memflags;
> > + /*
> > + * If we don't hold exclusive handle for the device, upgrade to it
> > + * here to avoid changing device under exclusive owner.
> > + */
> > + if (!(mode & BLK_OPEN_EXCL)) {
> > + err = bd_prepare_to_claim(bdev, loop_set_status, NULL);
> > + if (err)
> > + goto out_reread_partitions;
> > + }
> > +
>
> + if (mode & BLK_OPEN_EXCL) {
> + struct block_device *whole = bdev_whole(bdev);
> +
> + BUG_ON(whole->bd_claiming == NULL);
> + }
>
> I add the above code and do the following test:
> # losetup -f data.1g
> # echo "0 `blockdev --getsz /dev/loop0` linear /dev/loop0 0" | dmsetup
> create my-linear
> # ./ioctl-test /dev/mapper/my-linear // trigger BUG_ON, ioctl-test.c is
> in attachment.
>
> The root causes of BUG_ON:
> 1. When creating 'my-linear' device, the mode for opening /dev/loop0
> does not include the BLK_OPEN_EXCL flag.
> table_load
> - dm_table_create // get_mode() never assign BLK_OPEN_EXCL to {struct
> dm_table *t}->mode
> - populate_table
> - dm_table_add_target
> - linear_ctr
> - dm_get_device // mode = {struct dm_table *t}->mode, never open
> loop0 with BLK_OPEN_EXCL mode.
BLK_OPEN_EXCL is added by bdev_open() whenever it is called with non-NULL
holder. And DM code (open_table_device()) calls bdev_file_open_by_dev() with
_dm_claim_ptr as the holder. So all opens from DM should be exclusive ones.
The question obviously is what is broken in this that your reproducer still
works...
Honza
> 2. When 'my-linear' device is opened with the O_EXCL flag, and an ioctl
> is issued to it. The dm_blk_ioctl function calls bdev->bd_disk->fops-
> > ioctl(bdev, mode, cmd, arg), which passes the mode with BLK_OPEN_EXCL
> flag to lo_ioctl.
>
> 3. loop0 was not opened by dm_get_device() in BLK_OPEN_EXCL mode. As a
> result, whole->bd_claiming is NULL.
>
> Thus, the BLK_OPEN_EXCL flag in the mode passed to lo_ioctl doesn't
> guarantee the loop device was opened with BLK_OPEN_EXCL.
>
> How about use per-device rw_semaphore instead of 'bd_prepare_to_claim/
> bd_abort_claiming'?
>
> Yongpeng,
>
> > err = mutex_lock_killable(&lo->lo_mutex);
> > if (err)
> > return err;
> > @@ -1270,6 +1281,9 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
> > }
> > out_unlock:
> > mutex_unlock(&lo->lo_mutex);
> > + if (!(mode & BLK_OPEN_EXCL))
> > + bd_abort_claiming(bdev, loop_set_status);
> > +out_reread_partitions:
> > if (partscan)
> > loop_reread_partitions(lo);
> > @@ -1349,7 +1363,9 @@ loop_info64_to_old(const struct loop_info64 *info64, struct loop_info *info)
> > }
> > static int
> > -loop_set_status_old(struct loop_device *lo, const struct loop_info __user *arg)
> > +loop_set_status_old(struct loop_device *lo, blk_mode_t mode,
> > + struct block_device *bdev,
> > + const struct loop_info __user *arg)
> > {
> > struct loop_info info;
> > struct loop_info64 info64;
> > @@ -1357,17 +1373,19 @@ loop_set_status_old(struct loop_device *lo, const struct loop_info __user *arg)
> > if (copy_from_user(&info, arg, sizeof (struct loop_info)))
> > return -EFAULT;
> > loop_info64_from_old(&info, &info64);
> > - return loop_set_status(lo, &info64);
> > + return loop_set_status(lo, mode, bdev, &info64);
> > }
> > static int
> > -loop_set_status64(struct loop_device *lo, const struct loop_info64 __user *arg)
> > +loop_set_status64(struct loop_device *lo, blk_mode_t mode,
> > + struct block_device *bdev,
> > + const struct loop_info64 __user *arg)
> > {
> > struct loop_info64 info64;
> > if (copy_from_user(&info64, arg, sizeof (struct loop_info64)))
> > return -EFAULT;
> > - return loop_set_status(lo, &info64);
> > + return loop_set_status(lo, mode, bdev, &info64);
> > }
> > static int
> > @@ -1546,14 +1564,14 @@ static int lo_ioctl(struct block_device *bdev, blk_mode_t mode,
> > case LOOP_SET_STATUS:
> > err = -EPERM;
> > if ((mode & BLK_OPEN_WRITE) || capable(CAP_SYS_ADMIN))
> > - err = loop_set_status_old(lo, argp);
> > + err = loop_set_status_old(lo, mode, bdev, argp);
> > break;
> > case LOOP_GET_STATUS:
> > return loop_get_status_old(lo, argp);
> > case LOOP_SET_STATUS64:
> > err = -EPERM;
> > if ((mode & BLK_OPEN_WRITE) || capable(CAP_SYS_ADMIN))
> > - err = loop_set_status64(lo, argp);
> > + err = loop_set_status64(lo, mode, bdev, argp);
> > break;
> > case LOOP_GET_STATUS64:
> > return loop_get_status64(lo, argp);
> > @@ -1647,8 +1665,9 @@ loop_info64_to_compat(const struct loop_info64 *info64,
> > }
> > static int
> > -loop_set_status_compat(struct loop_device *lo,
> > - const struct compat_loop_info __user *arg)
> > +loop_set_status_compat(struct loop_device *lo, blk_mode_t mode,
> > + struct block_device *bdev,
> > + const struct compat_loop_info __user *arg)
> > {
> > struct loop_info64 info64;
> > int ret;
> > @@ -1656,7 +1675,7 @@ loop_set_status_compat(struct loop_device *lo,
> > ret = loop_info64_from_compat(arg, &info64);
> > if (ret < 0)
> > return ret;
> > - return loop_set_status(lo, &info64);
> > + return loop_set_status(lo, mode, bdev, &info64);
> > }
> > static int
> > @@ -1682,7 +1701,7 @@ static int lo_compat_ioctl(struct block_device *bdev, blk_mode_t mode,
> > switch(cmd) {
> > case LOOP_SET_STATUS:
> > - err = loop_set_status_compat(lo,
> > + err = loop_set_status_compat(lo, mode, bdev,
> > (const struct compat_loop_info __user *)arg);
> > break;
> > case LOOP_GET_STATUS:
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
On 12/1/25 20:38, Jan Kara wrote:
> On Tue 18-11-25 15:10:20, Yongpeng Yang wrote:
>> On 11/14/25 22:42, Raphael Pinsonneault-Thibeault wrote:
>>> loop_set_status() is allowed to change the loop device while there
>>> are other openers of the device, even exclusive ones.
>>>
>>> In this case, it causes a KASAN: slab-out-of-bounds Read in
>>> ext4_search_dir(), since when looking for an entry in an inlined
>>> directory, e_value_offs is changed underneath the filesystem by
>>> loop_set_status().
>>>
>>> Fix the problem by forbidding loop_set_status() from modifying the loop
>>> device while there are exclusive openers of the device. This is similar
>>> to the fix in loop_configure() by commit 33ec3e53e7b1 ("loop: Don't
>>> change loop device under exclusive opener") alongside commit ecbe6bc0003b
>>> ("block: use bd_prepare_to_claim directly in the loop driver").
>>>
>>> Reported-by: syzbot+3ee481e21fd75e14c397@syzkaller.appspotmail.com
>>> Closes: https://syzkaller.appspot.com/bug?extid=3ee481e21fd75e14c397
>>> Tested-by: syzbot+3ee481e21fd75e14c397@syzkaller.appspotmail.com
>>> Signed-off-by: Raphael Pinsonneault-Thibeault <rpthibeault@gmail.com>
>>> ---
>>> ML thread for previous, misguided patch idea:
>>> https://lore.kernel.org/all/20251112185712.2031993-2-rpthibeault@gmail.com/t/
>>>
>>> drivers/block/loop.c | 41 ++++++++++++++++++++++++++++++-----------
>>> 1 file changed, 30 insertions(+), 11 deletions(-)
>>>
>>> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
>>> index 053a086d547e..756ee682e767 100644
>>> --- a/drivers/block/loop.c
>>> +++ b/drivers/block/loop.c
>>> @@ -1222,13 +1222,24 @@ static int loop_clr_fd(struct loop_device *lo)
>>> }
>>> static int
>>> -loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
>>> +loop_set_status(struct loop_device *lo, blk_mode_t mode,
>>> + struct block_device *bdev, const struct loop_info64 *info)
>>> {
>>> int err;
>>> bool partscan = false;
>>> bool size_changed = false;
>>> unsigned int memflags;
>>> + /*
>>> + * If we don't hold exclusive handle for the device, upgrade to it
>>> + * here to avoid changing device under exclusive owner.
>>> + */
>>> + if (!(mode & BLK_OPEN_EXCL)) {
>>> + err = bd_prepare_to_claim(bdev, loop_set_status, NULL);
>>> + if (err)
>>> + goto out_reread_partitions;
>>> + }
>>> +
>>
>> + if (mode & BLK_OPEN_EXCL) {
>> + struct block_device *whole = bdev_whole(bdev);
>> +
>> + BUG_ON(whole->bd_claiming == NULL);
>> + }
>>
>> I add the above code and do the following test:
>> # losetup -f data.1g
>> # echo "0 `blockdev --getsz /dev/loop0` linear /dev/loop0 0" | dmsetup
>> create my-linear
>> # ./ioctl-test /dev/mapper/my-linear // trigger BUG_ON, ioctl-test.c is
>> in attachment.
>>
>> The root causes of BUG_ON:
>> 1. When creating 'my-linear' device, the mode for opening /dev/loop0
>> does not include the BLK_OPEN_EXCL flag.
>> table_load
>> - dm_table_create // get_mode() never assign BLK_OPEN_EXCL to {struct
>> dm_table *t}->mode
>> - populate_table
>> - dm_table_add_target
>> - linear_ctr
>> - dm_get_device // mode = {struct dm_table *t}->mode, never open
>> loop0 with BLK_OPEN_EXCL mode.
>
> BLK_OPEN_EXCL is added by bdev_open() whenever it is called with non-NULL
> holder. And DM code (open_table_device()) calls bdev_file_open_by_dev() with
> _dm_claim_ptr as the holder. So all opens from DM should be exclusive ones.
> The question obviously is what is broken in this that your reproducer still
> works...
>
> Honza
>
Yes, I was mistaken. When loop0's whole->bd_claiming is NULL,
bdev->bd_holder is set to _dm_claim_ptr by bd_finish_claiming. When the
my-linear device is opened with BLK_OPEN_EXCL, its ioctls are handled
normally. If the my-linear device is opened without BLK_OPEN_EXCL, the
ioctl call returns -EBUSY, which is the expected behavior.
bdev_open
- bd_prepare_to_claim //whole->bd_claiming = _dm_claim_ptr;
- bd_finish_claiming // whole->bd_holder = bd_may_claim;
bdev->bd_holder = _dm_claim_ptr;
- bd_clear_claiming // whole->bd_claiming = NULL;
Tested-by: Yongpeng Yang <yangyongpeng@xiaomi.com>
Yongpeng,
>> 2. When 'my-linear' device is opened with the O_EXCL flag, and an ioctl
>> is issued to it. The dm_blk_ioctl function calls bdev->bd_disk->fops-
>>> ioctl(bdev, mode, cmd, arg), which passes the mode with BLK_OPEN_EXCL
>> flag to lo_ioctl.
>>
>> 3. loop0 was not opened by dm_get_device() in BLK_OPEN_EXCL mode. As a
>> result, whole->bd_claiming is NULL.
>>
>> Thus, the BLK_OPEN_EXCL flag in the mode passed to lo_ioctl doesn't
>> guarantee the loop device was opened with BLK_OPEN_EXCL.
>>
>> How about use per-device rw_semaphore instead of 'bd_prepare_to_claim/
>> bd_abort_claiming'?
>>
>> Yongpeng,
>>
>>> err = mutex_lock_killable(&lo->lo_mutex);
>>> if (err)
>>> return err;
>>> @@ -1270,6 +1281,9 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
>>> }
>>> out_unlock:
>>> mutex_unlock(&lo->lo_mutex);
>>> + if (!(mode & BLK_OPEN_EXCL))
>>> + bd_abort_claiming(bdev, loop_set_status);
>>> +out_reread_partitions:
>>> if (partscan)
>>> loop_reread_partitions(lo);
>>> @@ -1349,7 +1363,9 @@ loop_info64_to_old(const struct loop_info64 *info64, struct loop_info *info)
>>> }
>>> static int
>>> -loop_set_status_old(struct loop_device *lo, const struct loop_info __user *arg)
>>> +loop_set_status_old(struct loop_device *lo, blk_mode_t mode,
>>> + struct block_device *bdev,
>>> + const struct loop_info __user *arg)
>>> {
>>> struct loop_info info;
>>> struct loop_info64 info64;
>>> @@ -1357,17 +1373,19 @@ loop_set_status_old(struct loop_device *lo, const struct loop_info __user *arg)
>>> if (copy_from_user(&info, arg, sizeof (struct loop_info)))
>>> return -EFAULT;
>>> loop_info64_from_old(&info, &info64);
>>> - return loop_set_status(lo, &info64);
>>> + return loop_set_status(lo, mode, bdev, &info64);
>>> }
>>> static int
>>> -loop_set_status64(struct loop_device *lo, const struct loop_info64 __user *arg)
>>> +loop_set_status64(struct loop_device *lo, blk_mode_t mode,
>>> + struct block_device *bdev,
>>> + const struct loop_info64 __user *arg)
>>> {
>>> struct loop_info64 info64;
>>> if (copy_from_user(&info64, arg, sizeof (struct loop_info64)))
>>> return -EFAULT;
>>> - return loop_set_status(lo, &info64);
>>> + return loop_set_status(lo, mode, bdev, &info64);
>>> }
>>> static int
>>> @@ -1546,14 +1564,14 @@ static int lo_ioctl(struct block_device *bdev, blk_mode_t mode,
>>> case LOOP_SET_STATUS:
>>> err = -EPERM;
>>> if ((mode & BLK_OPEN_WRITE) || capable(CAP_SYS_ADMIN))
>>> - err = loop_set_status_old(lo, argp);
>>> + err = loop_set_status_old(lo, mode, bdev, argp);
>>> break;
>>> case LOOP_GET_STATUS:
>>> return loop_get_status_old(lo, argp);
>>> case LOOP_SET_STATUS64:
>>> err = -EPERM;
>>> if ((mode & BLK_OPEN_WRITE) || capable(CAP_SYS_ADMIN))
>>> - err = loop_set_status64(lo, argp);
>>> + err = loop_set_status64(lo, mode, bdev, argp);
>>> break;
>>> case LOOP_GET_STATUS64:
>>> return loop_get_status64(lo, argp);
>>> @@ -1647,8 +1665,9 @@ loop_info64_to_compat(const struct loop_info64 *info64,
>>> }
>>> static int
>>> -loop_set_status_compat(struct loop_device *lo,
>>> - const struct compat_loop_info __user *arg)
>>> +loop_set_status_compat(struct loop_device *lo, blk_mode_t mode,
>>> + struct block_device *bdev,
>>> + const struct compat_loop_info __user *arg)
>>> {
>>> struct loop_info64 info64;
>>> int ret;
>>> @@ -1656,7 +1675,7 @@ loop_set_status_compat(struct loop_device *lo,
>>> ret = loop_info64_from_compat(arg, &info64);
>>> if (ret < 0)
>>> return ret;
>>> - return loop_set_status(lo, &info64);
>>> + return loop_set_status(lo, mode, bdev, &info64);
>>> }
>>> static int
>>> @@ -1682,7 +1701,7 @@ static int lo_compat_ioctl(struct block_device *bdev, blk_mode_t mode,
>>> switch(cmd) {
>>> case LOOP_SET_STATUS:
>>> - err = loop_set_status_compat(lo,
>>> + err = loop_set_status_compat(lo, mode, bdev,
>>> (const struct compat_loop_info __user *)arg);
>>> break;
>>> case LOOP_GET_STATUS:
>
>
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