[lvc-project] [PATCH] exfat: bail out on -EIO in exfat_find_empty_entry()

[Namjae Jeon]

On Sat, Dec 14, 2024 at 1:18 AM Dmitry Antipov <dmantipov at yandex.ru> wrote:
>
> Syzbot has reported the following KASAN splat:
>
> KASAN: null-ptr-deref in range [0x0000000000000028-0x000000000000002f]
> ...
> Call Trace:
>  <TASK>
>  ...
>  ? exfat_get_dentry_cached+0xb6/0x1b0
>  ? exfat_get_dentry_cached+0x11a/0x1b0
>  ? exfat_get_dentry_cached+0xb6/0x1b0
>  exfat_init_ext_entry+0x1b6/0x3b0
>  exfat_add_entry+0x321/0x7a0
>  ? __pfx_exfat_add_entry+0x10/0x10
>  ? __lock_acquire+0x15a9/0x3c40
>  ? __pfx___lock_acquire+0x10/0x10
>  ? _raw_spin_unlock_irqrestore+0x52/0x80
>  ? do_raw_spin_unlock+0x53/0x230
>  ? _raw_spin_unlock+0x28/0x50
>  ? exfat_set_vol_flags+0x23f/0x2f0
>  exfat_create+0x1cf/0x5c0
>  ...
>  path_openat+0x904/0x2d60
>  ? __pfx_path_openat+0x10/0x10
>  ? __pfx___lock_acquire+0x10/0x10
>  ? lock_acquire.part.0+0x11b/0x380
>  ? find_held_lock+0x2d/0x110
>  do_filp_open+0x20c/0x470
>  ? __pfx_do_filp_open+0x10/0x10
>  ? find_held_lock+0x2d/0x110
>  ? _raw_spin_unlock+0x28/0x50
>  ? alloc_fd+0x41f/0x760
>  do_sys_openat2+0x17a/0x1e0
>  ? __pfx_do_sys_openat2+0x10/0x10
>  ? __pfx_sigprocmask+0x10/0x10
>  __x64_sys_creat+0xcd/0x120
>  ...
> </TASK>
>
> On exFAT with damaged directory structure, 'exfat_search_empty_slot()'
> may issue an attempt to access beyond end of device and return -EIO.
> So catch this error in 'exfat_find_empty_entry()', do not create an
> invalid in-memory directory structure and do not confuse the rest
> of the filesystem code further.
>
> Reported-by: syzbot+8f8fe64a30c50b289a18 at syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=8f8fe64a30c50b289a18
> Fixes: 5f2aa075070c ("exfat: add inode operations")
> Signed-off-by: Dmitry Antipov <dmantipov at yandex.ru>
> ---
>  fs/exfat/namei.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/exfat/namei.c b/fs/exfat/namei.c
> index 97d2774760fe..73dbc5cdf388 100644
> --- a/fs/exfat/namei.c
> +++ b/fs/exfat/namei.c
> @@ -331,7 +331,7 @@ static int exfat_find_empty_entry(struct inode *inode,
>         while ((dentry = exfat_search_empty_slot(sb, &hint_femp, p_dir,
>                                         num_entries, es)) < 0) {
>                 if (dentry == -EIO)
> -                       break;
> +                       return -EIO;
Sorry, I have already applied Yuezhang's patch that fixed this issue.
https://git.kernel.org/pub/scm/linux/kernel/git/linkinjeon/exfat.git/commit/?h=dev&id=744e50c7e25a0e743f30003137f8413dcd107bb0

Thanks.
>
>                 if (exfat_check_max_dentries(inode))
>                         return -ENOSPC;
> --
> 2.47.1
>