fs/ext4/extents.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-)
If the starting position of our insert range happens to be in the hole
between the two ext4_extent_idx, because the lblk of the ext4_extent in
the previous ext4_extent_idx is always less than the start, which leads
to the "extent" variable access across the boundary, the following UAF is
triggered:
==================================================================
BUG: KASAN: use-after-free in ext4_ext_shift_extents+0x257/0x790
Read of size 4 at addr ffff88819807a008 by task fallocate/8010
CPU: 3 PID: 8010 Comm: fallocate Tainted: G E 5.10.0+ #492
Call Trace:
dump_stack+0x7d/0xa3
print_address_description.constprop.0+0x1e/0x220
kasan_report.cold+0x67/0x7f
ext4_ext_shift_extents+0x257/0x790
ext4_insert_range+0x5b6/0x700
ext4_fallocate+0x39e/0x3d0
vfs_fallocate+0x26f/0x470
ksys_fallocate+0x3a/0x70
__x64_sys_fallocate+0x4f/0x60
do_syscall_64+0x33/0x40
entry_SYSCALL_64_after_hwframe+0x44/0xa9
==================================================================
For right shifts, we can divide them into the following situations：
1. When the first ee_block of ext4_extent_idx is greater than or equal to
start, make right shifts directly from the first ee_block.
1) If it is greater than start, we need to continue searching in the
previous ext4_extent_idx.
2) If it is equal to start, we can exit the loop (iterator=NULL).
2. When the first ee_block of ext4_extent_idx is less than start, then
traverse from the last extent to find the first extent whose ee_block
is less than start.
1) If extent is still the last extent after traversal, it means that
the last ee_block of ext4_extent_idx is less than start, that is,
start is located in the hole between idx and (idx+1), so we can
exit the loop directly (break) without right shifts.
2) Otherwise, make right shifts at the corresponding position of the
found extent, and then exit the loop (iterator=NULL).
Fixes: 331573febb6a ("ext4: Add support FALLOC_FL_INSERT_RANGE for fallocate")
Cc: stable@vger.kernel.org # v4.2+
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Baokun Li <libaokun1@huawei.com>
---
V1->V2:
Initialize "ret" after the "again:" label to avoid return value mismatch.
Refactoring reduces cycles and makes code more readable.
fs/ext4/extents.c | 18 +++++++++++++-----
1 file changed, 13 insertions(+), 5 deletions(-)
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index c148bb97b527..39c9f87de0be 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -5179,6 +5179,7 @@ ext4_ext_shift_extents(struct inode *inode, handle_t *handle,
* and it is decreased till we reach start.
*/
again:
+ ret = 0;
if (SHIFT == SHIFT_LEFT)
iterator = &start;
else
@@ -5222,14 +5223,21 @@ ext4_ext_shift_extents(struct inode *inode, handle_t *handle,
ext4_ext_get_actual_len(extent);
} else {
extent = EXT_FIRST_EXTENT(path[depth].p_hdr);
- if (le32_to_cpu(extent->ee_block) > 0)
+ if (le32_to_cpu(extent->ee_block) > start)
*iterator = le32_to_cpu(extent->ee_block) - 1;
- else
- /* Beginning is reached, end of the loop */
+ else if (le32_to_cpu(extent->ee_block) == start)
iterator = NULL;
- /* Update path extent in case we need to stop */
- while (le32_to_cpu(extent->ee_block) < start)
+ else {
+ extent = EXT_LAST_EXTENT(path[depth].p_hdr);
+ while (le32_to_cpu(extent->ee_block) >= start)
+ extent--;
+
+ if (extent == EXT_LAST_EXTENT(path[depth].p_hdr))
+ break;
+
extent++;
+ iterator = NULL;
+ }
path[depth].p_ext = extent;
}
ret = ext4_ext_shift_path_extents(path, shift, inode,
--
2.31.1
On Thu, 22 Sep 2022 20:04:34 +0800, Baokun Li wrote:
> If the starting position of our insert range happens to be in the hole
> between the two ext4_extent_idx, because the lblk of the ext4_extent in
> the previous ext4_extent_idx is always less than the start, which leads
> to the "extent" variable access across the boundary, the following UAF is
> triggered:
> ==================================================================
> BUG: KASAN: use-after-free in ext4_ext_shift_extents+0x257/0x790
> Read of size 4 at addr ffff88819807a008 by task fallocate/8010
> CPU: 3 PID: 8010 Comm: fallocate Tainted: G E 5.10.0+ #492
> Call Trace:
> dump_stack+0x7d/0xa3
> print_address_description.constprop.0+0x1e/0x220
> kasan_report.cold+0x67/0x7f
> ext4_ext_shift_extents+0x257/0x790
> ext4_insert_range+0x5b6/0x700
> ext4_fallocate+0x39e/0x3d0
> vfs_fallocate+0x26f/0x470
> ksys_fallocate+0x3a/0x70
> __x64_sys_fallocate+0x4f/0x60
> do_syscall_64+0x33/0x40
> entry_SYSCALL_64_after_hwframe+0x44/0xa9
> ==================================================================
>
> [...]
Applied, thanks!
[1/1] ext4: fix use-after-free in ext4_ext_shift_extents
(no commit info)
Best regards,
--
Theodore Ts'o <tytso@mit.edu>
On 2022/9/30 11:19, Theodore Ts'o wrote: > On Thu, 22 Sep 2022 20:04:34 +0800, Baokun Li wrote: >> If the starting position of our insert range happens to be in the hole >> between the two ext4_extent_idx, because the lblk of the ext4_extent in >> the previous ext4_extent_idx is always less than the start, which leads >> to the "extent" variable access across the boundary, the following UAF is >> triggered: >> ================================================================== >> BUG: KASAN: use-after-free in ext4_ext_shift_extents+0x257/0x790 >> Read of size 4 at addr ffff88819807a008 by task fallocate/8010 >> CPU: 3 PID: 8010 Comm: fallocate Tainted: G E 5.10.0+ #492 >> Call Trace: >> dump_stack+0x7d/0xa3 >> print_address_description.constprop.0+0x1e/0x220 >> kasan_report.cold+0x67/0x7f >> ext4_ext_shift_extents+0x257/0x790 >> ext4_insert_range+0x5b6/0x700 >> ext4_fallocate+0x39e/0x3d0 >> vfs_fallocate+0x26f/0x470 >> ksys_fallocate+0x3a/0x70 >> __x64_sys_fallocate+0x4f/0x60 >> do_syscall_64+0x33/0x40 >> entry_SYSCALL_64_after_hwframe+0x44/0xa9 >> ================================================================== >> >> [...] > Applied, thanks! > > [1/1] ext4: fix use-after-free in ext4_ext_shift_extents > (no commit info) > > Best regards, Hi Theodore, Could you tell me why this patch has been applied, but there is no cmmit info, and the patch cannot be found on any branch? -- With Best Regards, Baokun Li
On Thu 22-09-22 20:04:34, Baokun Li wrote:
> If the starting position of our insert range happens to be in the hole
> between the two ext4_extent_idx, because the lblk of the ext4_extent in
> the previous ext4_extent_idx is always less than the start, which leads
> to the "extent" variable access across the boundary, the following UAF is
> triggered:
> ==================================================================
> BUG: KASAN: use-after-free in ext4_ext_shift_extents+0x257/0x790
> Read of size 4 at addr ffff88819807a008 by task fallocate/8010
> CPU: 3 PID: 8010 Comm: fallocate Tainted: G E 5.10.0+ #492
> Call Trace:
> dump_stack+0x7d/0xa3
> print_address_description.constprop.0+0x1e/0x220
> kasan_report.cold+0x67/0x7f
> ext4_ext_shift_extents+0x257/0x790
> ext4_insert_range+0x5b6/0x700
> ext4_fallocate+0x39e/0x3d0
> vfs_fallocate+0x26f/0x470
> ksys_fallocate+0x3a/0x70
> __x64_sys_fallocate+0x4f/0x60
> do_syscall_64+0x33/0x40
> entry_SYSCALL_64_after_hwframe+0x44/0xa9
> ==================================================================
>
> For right shifts, we can divide them into the following situations：
>
> 1. When the first ee_block of ext4_extent_idx is greater than or equal to
> start, make right shifts directly from the first ee_block.
> 1) If it is greater than start, we need to continue searching in the
> previous ext4_extent_idx.
> 2) If it is equal to start, we can exit the loop (iterator=NULL).
>
> 2. When the first ee_block of ext4_extent_idx is less than start, then
> traverse from the last extent to find the first extent whose ee_block
> is less than start.
> 1) If extent is still the last extent after traversal, it means that
> the last ee_block of ext4_extent_idx is less than start, that is,
> start is located in the hole between idx and (idx+1), so we can
> exit the loop directly (break) without right shifts.
> 2) Otherwise, make right shifts at the corresponding position of the
> found extent, and then exit the loop (iterator=NULL).
>
> Fixes: 331573febb6a ("ext4: Add support FALLOC_FL_INSERT_RANGE for fallocate")
> Cc: stable@vger.kernel.org # v4.2+
> Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
> Signed-off-by: Baokun Li <libaokun1@huawei.com>
Thanks for the fix! It looks good to me. Feel free to add:
Reviewed-by: Jan Kara <jack@suse.cz>
Honza
> ---
> V1->V2:
> Initialize "ret" after the "again:" label to avoid return value mismatch.
> Refactoring reduces cycles and makes code more readable.
>
> fs/ext4/extents.c | 18 +++++++++++++-----
> 1 file changed, 13 insertions(+), 5 deletions(-)
>
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index c148bb97b527..39c9f87de0be 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -5179,6 +5179,7 @@ ext4_ext_shift_extents(struct inode *inode, handle_t *handle,
> * and it is decreased till we reach start.
> */
> again:
> + ret = 0;
> if (SHIFT == SHIFT_LEFT)
> iterator = &start;
> else
> @@ -5222,14 +5223,21 @@ ext4_ext_shift_extents(struct inode *inode, handle_t *handle,
> ext4_ext_get_actual_len(extent);
> } else {
> extent = EXT_FIRST_EXTENT(path[depth].p_hdr);
> - if (le32_to_cpu(extent->ee_block) > 0)
> + if (le32_to_cpu(extent->ee_block) > start)
> *iterator = le32_to_cpu(extent->ee_block) - 1;
> - else
> - /* Beginning is reached, end of the loop */
> + else if (le32_to_cpu(extent->ee_block) == start)
> iterator = NULL;
> - /* Update path extent in case we need to stop */
> - while (le32_to_cpu(extent->ee_block) < start)
> + else {
> + extent = EXT_LAST_EXTENT(path[depth].p_hdr);
> + while (le32_to_cpu(extent->ee_block) >= start)
> + extent--;
> +
> + if (extent == EXT_LAST_EXTENT(path[depth].p_hdr))
> + break;
> +
> extent++;
> + iterator = NULL;
> + }
> path[depth].p_ext = extent;
> }
> ret = ext4_ext_shift_path_extents(path, shift, inode,
> --
> 2.31.1
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
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