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,
> + 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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