Hi:
When using Healer(https://github.com/SunHao-0/healer/tree/dev) to fuzz
the Linux kernel, I found a data-race vulnerability in ext4_fc_commit
/ ext4_fc_commit, which looks strange.
Sorry, data-race is usually difficult to reproduce. I cannot provide
you with a reproducing program.
I hope that the call stack information in the crash log can help you
locate the problem.
Kernel config and full log can be found in the attachment.
Here is the detailed information:
commit: 3b9cdafb5358eb9f3790de2f728f765fef100731
version: linux 5.11
git tree: upstream
report:
==================================================================
BUG: KCSAN: data-race in ext4_fc_commit / ext4_fc_commit
write to 0xffff88800dd89f10 of 8 bytes by task 12063 on cpu 0:
ext4_fc_commit+0x1e6/0x1850 linux/fs/ext4/fast_commit.c:1205
ext4_fsync_journal linux/fs/ext4/fsync.c:115 [inline]
ext4_sync_file+0x38c/0x6d0 linux/fs/ext4/fsync.c:174
vfs_fsync_range linux/fs/sync.c:200 [inline]
vfs_fsync linux/fs/sync.c:214 [inline]
do_fsync linux/fs/sync.c:224 [inline]
__do_sys_fdatasync linux/fs/sync.c:237 [inline]
__se_sys_fdatasync linux/fs/sync.c:235 [inline]
__x64_sys_fdatasync+0x7a/0xd0 linux/fs/sync.c:235
do_syscall_64+0x39/0x80 linux/arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xae
Thanks for the report Hao! I think following lines in fast_commit.c
are the culprit:
if (likely(sbi->s_fc_avg_commit_time))
sbi->s_fc_avg_commit_time = (commit_time +
sbi->s_fc_avg_commit_time * 3) / 4;
else
sbi->s_fc_avg_commit_time = commit_time;
This should have been done after taking sbi level lock, but this is
happening after releasing the lock.
I'll send a patch to fix this, thanks again!
- Harshad
On Sun, Apr 4, 2021 at 2:52 AM Hao Sun <[email protected]> wrote:
>
> Hi:
>
> When using Healer(https://github.com/SunHao-0/healer/tree/dev) to fuzz
> the Linux kernel, I found a data-race vulnerability in ext4_fc_commit
> / ext4_fc_commit, which looks strange.
> Sorry, data-race is usually difficult to reproduce. I cannot provide
> you with a reproducing program.
> I hope that the call stack information in the crash log can help you
> locate the problem.
> Kernel config and full log can be found in the attachment.
>
> Here is the detailed information:
> commit: 3b9cdafb5358eb9f3790de2f728f765fef100731
> version: linux 5.11
> git tree: upstream
> report:
> ==================================================================
> BUG: KCSAN: data-race in ext4_fc_commit / ext4_fc_commit
> write to 0xffff88800dd89f10 of 8 bytes by task 12063 on cpu 0:
> ext4_fc_commit+0x1e6/0x1850 linux/fs/ext4/fast_commit.c:1205
> ext4_fsync_journal linux/fs/ext4/fsync.c:115 [inline]
> ext4_sync_file+0x38c/0x6d0 linux/fs/ext4/fsync.c:174
> vfs_fsync_range linux/fs/sync.c:200 [inline]
> vfs_fsync linux/fs/sync.c:214 [inline]
> do_fsync linux/fs/sync.c:224 [inline]
> __do_sys_fdatasync linux/fs/sync.c:237 [inline]
> __se_sys_fdatasync linux/fs/sync.c:235 [inline]
> __x64_sys_fdatasync+0x7a/0xd0 linux/fs/sync.c:235
> do_syscall_64+0x39/0x80 linux/arch/x86/entry/common.c:46
> entry_SYSCALL_64_after_hwframe+0x44/0xae