On 11/3/25 15:55, Nikola Z. Ivanov wrote:
> On Mon, Nov 03, 2025 at 10:35:17AM +0800, Chao Yu wrote:
>> On 11/1/25 20:56, Nikola Z. Ivanov wrote:
>>> Add check for inode->i_nlink == 1 for directories during unlink,
>>> as their value is decremented twice, which can trigger a warning in
>>> drop_nlink. In such case mark the filesystem as corrupted and return
>>> from the function call with the relevant failure return value.
>>>
>>> Additionally add the 2 checks for i_nlink == 0 and i_nlink == 1 in
>>> sanity_check_inode in order to detect on-disk corruption early.
>>>
>>> Reported-by: [email protected]
>>> Closes: https://syzkaller.appspot.com/bug?extid=c07d47c7bc68f47b9083
>>> Tested-by: [email protected]
>>> Signed-off-by: Nikola Z. Ivanov <[email protected]>
>>> ---
>>> fs/f2fs/inode.c | 10 ++++++++++
>>> fs/f2fs/namei.c | 15 +++++++++++----
>>> 2 files changed, 21 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
>>> index 8c4eafe9ffac..089cbf3646f0 100644
>>> --- a/fs/f2fs/inode.c
>>> +++ b/fs/f2fs/inode.c
>>> @@ -294,6 +294,16 @@ static bool sanity_check_inode(struct inode *inode,
>>> struct folio *node_folio)
>>> return false;
>>> }
>>>
>>> + if (unlikely(inode->i_nlink == 0)) {
>>
>> This is a possible case, as an orphan inode may exist in filesystem after
>> sudden
>> power-cut.
>>
>> Thanks,
>>
>
> Hi Chao,
>
> Do you suggest that it should not be wrapped in unlikely()?
Nikola,
No, I think we should not add this sanity check "inode->i_nlink == 0"
into sanity_check_inode(), as for an orphan inode, its i_nlink is zero.
We expect to get the inode w/o failure in recover_orphan_inode().
>
> I also now realise that I intended to wrap the "else if" case
> as well but I've missed it in the final patch.
Looks fine to add unlike for the "dir->i_nlink == 1" case.
Thanks,
>
> Should I resend the patch with both cases wrapped in "unlikely()"
> or would you suggest otherwise?
>
>
>>> + f2fs_warn(F2FS_I_SB(inode), "%s: inode (ino=%lx) has zero
>>> i_nlink",
>>> + __func__, inode->i_ino);
>>> + return false;
>>> + } else if (S_ISDIR(inode->i_mode) && inode->i_nlink == 1) {
>>> + f2fs_warn(F2FS_I_SB(inode), "%s: directory inode (ino=%lx) has
>>> a single i_nlink",
>>> + __func__, inode->i_ino);
>>> + return false;
>>> + }
>>> +
>>> if (f2fs_has_extra_attr(inode)) {
>>> if (!f2fs_sb_has_extra_attr(sbi)) {
>>> f2fs_warn(sbi, "%s: inode (ino=%lx) is with extra_attr,
>>> but extra_attr feature is off",
>>> diff --git a/fs/f2fs/namei.c b/fs/f2fs/namei.c
>>> index 40cf80fd9d9a..d13077bad482 100644
>>> --- a/fs/f2fs/namei.c
>>> +++ b/fs/f2fs/namei.c
>>> @@ -572,10 +572,11 @@ static int f2fs_unlink(struct inode *dir, struct
>>> dentry *dentry)
>>> if (unlikely(inode->i_nlink == 0)) {
>>> f2fs_warn(F2FS_I_SB(inode), "%s: inode (ino=%lx) has zero
>>> i_nlink",
>>> __func__, inode->i_ino);
>>> - err = -EFSCORRUPTED;
>>> - set_sbi_flag(F2FS_I_SB(inode), SBI_NEED_FSCK);
>>> - f2fs_folio_put(folio, false);
>>> - goto out;
>>> + goto corrupted;
>>> + } else if (S_ISDIR(inode->i_mode) && inode->i_nlink == 1) {
>>> + f2fs_warn(F2FS_I_SB(inode), "%s: directory inode (ino=%lx) has
>>> a single i_nlink",
>>> + __func__, inode->i_ino);
>>> + goto corrupted;
>>> }
>>>
>>> f2fs_balance_fs(sbi, true);
>>> @@ -601,6 +602,12 @@ static int f2fs_unlink(struct inode *dir, struct
>>> dentry *dentry)
>>>
>>> if (IS_DIRSYNC(dir))
>>> f2fs_sync_fs(sbi->sb, 1);
>>> +
>>> + goto out;
>>> +corrupted:
>>> + err = -EFSCORRUPTED;
>>> + set_sbi_flag(F2FS_I_SB(inode), SBI_NEED_FSCK);
>>> + f2fs_folio_put(folio, false);
>>> out:
>>> trace_f2fs_unlink_exit(inode, err);
>>> return err;
>>
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