fs/notify/fdinfo.c | 6 ++++++ 1 file changed, 6 insertions(+)
Calling intotify_show_fdinfo() on fd watching an overlayfs inode, while
the overlayfs is being unmounted, can lead to dereferencing NULL ptr.
This issue was found by syzkaller.
Race Condition Diagram:
Thread 1 Thread 2
-------- --------
generic_shutdown_super()
shrink_dcache_for_umount
sb->s_root = NULL
|
| vfs_read()
| inotify_fdinfo()
| * inode get from mark *
| show_mark_fhandle(m, inode)
| exportfs_encode_fid(inode, ..)
| ovl_encode_fh(inode, ..)
| ovl_check_encode_origin(inode)
| * deref i_sb->s_root *
|
|
v
fsnotify_sb_delete(sb)
Which then leads to:
[ 32.133461] Oops: general protection fault, probably for non-canonical address 0xdffffc0000000006: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN NOPTI
[ 32.134438] KASAN: null-ptr-deref in range [0x0000000000000030-0x0000000000000037]
[ 32.135032] CPU: 1 UID: 0 PID: 4468 Comm: systemd-coredum Not tainted 6.17.0-rc6 #22 PREEMPT(none)
<snip registers, unreliable trace>
[ 32.143353] Call Trace:
[ 32.143732] ovl_encode_fh+0xd5/0x170
[ 32.144031] exportfs_encode_inode_fh+0x12f/0x300
[ 32.144425] show_mark_fhandle+0xbe/0x1f0
[ 32.145805] inotify_fdinfo+0x226/0x2d0
[ 32.146442] inotify_show_fdinfo+0x1c5/0x350
[ 32.147168] seq_show+0x530/0x6f0
[ 32.147449] seq_read_iter+0x503/0x12a0
[ 32.148419] seq_read+0x31f/0x410
[ 32.150714] vfs_read+0x1f0/0x9e0
[ 32.152297] ksys_read+0x125/0x240
IOW ovl_check_encode_origin derefs inode->i_sb->s_root, after it was set
to NULL in the unmount path.
Fix it by protecting calling exportfs_encode_fid() from
show_mark_fhandle() with s_umount lock.
This form of fix was suggested by Amir in [1].
[1]: https://lore.kernel.org/all/CAOQ4uxhbDwhb+2Brs1UdkoF0a3NSdBAOQPNfEHjahrgoKJpLEw@mail.gmail.com/
Fixes: c45beebfde34 ("ovl: support encoding fid from inode with no alias")
Signed-off-by: Jakub Acs <acsjakub@amazon.de>
Cc: Jan Kara <jack@suse.cz>
Cc: Amir Goldstein <amir73il@gmail.com>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Christian Brauner <brauner@kernel.org>
Cc: linux-unionfs@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: stable@vger.kernel.org
---
This issue was already discussed in [1] with no consensus reached on the
fix.
This form was suggested as a band-aid fix, without explicity yes/no
reaction. Hence reviving the discussion around the band-aid.
fs/notify/fdinfo.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/fs/notify/fdinfo.c b/fs/notify/fdinfo.c
index 1161eabf11ee..9cc7eb863643 100644
--- a/fs/notify/fdinfo.c
+++ b/fs/notify/fdinfo.c
@@ -17,6 +17,7 @@
#include "fanotify/fanotify.h"
#include "fdinfo.h"
#include "fsnotify.h"
+#include "../internal.h"
#if defined(CONFIG_PROC_FS)
@@ -46,7 +47,12 @@ static void show_mark_fhandle(struct seq_file *m, struct inode *inode)
size = f->handle_bytes >> 2;
+ if (!super_trylock_shared(inode->i_sb))
+ return;
+
ret = exportfs_encode_fid(inode, (struct fid *)f->f_handle, &size);
+ up_read(&inode->i_sb->s_umount);
+
if ((ret == FILEID_INVALID) || (ret < 0))
return;
--
2.47.3
Amazon Web Services Development Center Germany GmbH
Tamara-Danz-Str. 13
10243 Berlin
Geschaeftsfuehrung: Christian Schlaeger
Eingetragen am Amtsgericht Charlottenburg unter HRB 257764 B
Sitz: Berlin
Ust-ID: DE 365 538 597On Wed 01-10-25 10:09:55, Jakub Acs wrote:
> Calling intotify_show_fdinfo() on fd watching an overlayfs inode, while
> the overlayfs is being unmounted, can lead to dereferencing NULL ptr.
>
> This issue was found by syzkaller.
>
> Race Condition Diagram:
>
> Thread 1 Thread 2
> -------- --------
>
> generic_shutdown_super()
> shrink_dcache_for_umount
> sb->s_root = NULL
>
> |
> | vfs_read()
> | inotify_fdinfo()
> | * inode get from mark *
> | show_mark_fhandle(m, inode)
> | exportfs_encode_fid(inode, ..)
> | ovl_encode_fh(inode, ..)
> | ovl_check_encode_origin(inode)
> | * deref i_sb->s_root *
> |
> |
> v
> fsnotify_sb_delete(sb)
>
> Which then leads to:
>
> [ 32.133461] Oops: general protection fault, probably for non-canonical address 0xdffffc0000000006: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN NOPTI
> [ 32.134438] KASAN: null-ptr-deref in range [0x0000000000000030-0x0000000000000037]
> [ 32.135032] CPU: 1 UID: 0 PID: 4468 Comm: systemd-coredum Not tainted 6.17.0-rc6 #22 PREEMPT(none)
>
> <snip registers, unreliable trace>
>
> [ 32.143353] Call Trace:
> [ 32.143732] ovl_encode_fh+0xd5/0x170
> [ 32.144031] exportfs_encode_inode_fh+0x12f/0x300
> [ 32.144425] show_mark_fhandle+0xbe/0x1f0
> [ 32.145805] inotify_fdinfo+0x226/0x2d0
> [ 32.146442] inotify_show_fdinfo+0x1c5/0x350
> [ 32.147168] seq_show+0x530/0x6f0
> [ 32.147449] seq_read_iter+0x503/0x12a0
> [ 32.148419] seq_read+0x31f/0x410
> [ 32.150714] vfs_read+0x1f0/0x9e0
> [ 32.152297] ksys_read+0x125/0x240
>
> IOW ovl_check_encode_origin derefs inode->i_sb->s_root, after it was set
> to NULL in the unmount path.
>
> Fix it by protecting calling exportfs_encode_fid() from
> show_mark_fhandle() with s_umount lock.
>
> This form of fix was suggested by Amir in [1].
>
> [1]: https://lore.kernel.org/all/CAOQ4uxhbDwhb+2Brs1UdkoF0a3NSdBAOQPNfEHjahrgoKJpLEw@mail.gmail.com/
>
> Fixes: c45beebfde34 ("ovl: support encoding fid from inode with no alias")
> Signed-off-by: Jakub Acs <acsjakub@amazon.de>
> Cc: Jan Kara <jack@suse.cz>
> Cc: Amir Goldstein <amir73il@gmail.com>
> Cc: Miklos Szeredi <miklos@szeredi.hu>
> Cc: Christian Brauner <brauner@kernel.org>
> Cc: linux-unionfs@vger.kernel.org
> Cc: linux-fsdevel@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Cc: stable@vger.kernel.org
> ---
>
> This issue was already discussed in [1] with no consensus reached on the
> fix.
>
> This form was suggested as a band-aid fix, without explicity yes/no
> reaction. Hence reviving the discussion around the band-aid.
FWIW I'm working on a proper fix. But it's a larger rework so it will take
some time to settle. For the time being, since this seems to happen in
practical workloads, I guess we can live with this workaround so I'll pick
this patch, add some comment about band-aid into the code and push it to
Linus. Thanks!
Honza
>
> fs/notify/fdinfo.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/fs/notify/fdinfo.c b/fs/notify/fdinfo.c
> index 1161eabf11ee..9cc7eb863643 100644
> --- a/fs/notify/fdinfo.c
> +++ b/fs/notify/fdinfo.c
> @@ -17,6 +17,7 @@
> #include "fanotify/fanotify.h"
> #include "fdinfo.h"
> #include "fsnotify.h"
> +#include "../internal.h"
>
> #if defined(CONFIG_PROC_FS)
>
> @@ -46,7 +47,12 @@ static void show_mark_fhandle(struct seq_file *m, struct inode *inode)
>
> size = f->handle_bytes >> 2;
>
> + if (!super_trylock_shared(inode->i_sb))
> + return;
> +
> ret = exportfs_encode_fid(inode, (struct fid *)f->f_handle, &size);
> + up_read(&inode->i_sb->s_umount);
> +
> if ((ret == FILEID_INVALID) || (ret < 0))
> return;
>
> --
> 2.47.3
>
>
>
>
> Amazon Web Services Development Center Germany GmbH
> Tamara-Danz-Str. 13
> 10243 Berlin
> Geschaeftsfuehrung: Christian Schlaeger
> Eingetragen am Amtsgericht Charlottenburg unter HRB 257764 B
> Sitz: Berlin
> Ust-ID: DE 365 538 597
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
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