On 10/14/25 20:17, Nikola Z. Ivanov wrote: > On Mon, Oct 13, 2025 at 08:53:04PM +0800, Chao Yu wrote: >> On 10/13/25 05:19, Nikola Z. Ivanov wrote: >>> On Thu, Oct 09, 2025 at 10:54:40AM +0800, Chao Yu wrote: >>>> On 10/3/2025 9:47 PM, Nikola Z. Ivanov wrote: >>>>> Current i_nlink corruption check does not take into account >>>>> directory inodes which have one additional i_nlink for their "." entry. >>>>> >>>>> Add additional check and a common corruption path. >>>>> >>>>> Reported-by: [email protected] >>>>> Closes: https://syzkaller.appspot.com/bug?extid=c07d47c7bc68f47b9083 >>>>> Fixes: 81edb983b3f5 ("f2fs: add check for deleted inode") >>>>> Signed-off-by: Nikola Z. Ivanov <[email protected]> >>>>> --- >>>>> fs/f2fs/namei.c | 28 ++++++++++++++++++++-------- >>>>> 1 file changed, 20 insertions(+), 8 deletions(-) >>>>> >>>>> diff --git a/fs/f2fs/namei.c b/fs/f2fs/namei.c >>>>> index b882771e4699..68b33e8089b0 100644 >>>>> --- a/fs/f2fs/namei.c >>>>> +++ b/fs/f2fs/namei.c >>>>> @@ -502,12 +502,14 @@ static struct dentry *f2fs_lookup(struct inode >>>>> *dir, struct dentry *dentry, >>>>> goto out; >>>>> } >>>>> - if (inode->i_nlink == 0) { >>>>> + 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); >>>>> - goto out_iput; >>>>> + goto corrupted; >>>>> + } else if (unlikely(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; >>>> >>>> Can we detect such corruption in sanity_check_inode() as well? So that if >>>> f2fs internal flow calls f2fs_iget() on corrupted inode, we can set >>>> SBI_NEED_FSCK >>>> flag and then triggering fsck repairment later. >>>> >>>> Thanks, >>>> >>>>> } >>>>> if (IS_ENCRYPTED(dir) && >>>>> @@ -533,6 +535,9 @@ static struct dentry *f2fs_lookup(struct inode *dir, >>>>> struct dentry *dentry, >>>>> trace_f2fs_lookup_end(dir, !IS_ERR_OR_NULL(new) ? new : dentry, >>>>> ino, IS_ERR(new) ? PTR_ERR(new) : err); >>>>> return new; >>>>> +corrupted: >>>>> + err = -EFSCORRUPTED; >>>>> + set_sbi_flag(F2FS_I_SB(inode), SBI_NEED_FSCK); >>>>> out_iput: >>>>> iput(inode); >>>>> out: >>>>> @@ -572,10 +577,11 @@ 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 fail; >>>>> + goto corrupted; >>>>> + } else if (unlikely(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 +607,12 @@ static int f2fs_unlink(struct inode *dir, struct >>>>> dentry *dentry) >>>>> if (IS_DIRSYNC(dir)) >>>>> f2fs_sync_fs(sbi->sb, 1); >>>>> + >>>>> + goto fail; >>>>> +corrupted: >>>>> + err = -EFSCORRUPTED; >>>>> + set_sbi_flag(F2FS_I_SB(inode), SBI_NEED_FSCK); >>>>> + f2fs_folio_put(folio, false); >>>>> fail: >>>>> trace_f2fs_unlink_exit(inode, err); >>>>> return err; >>>> >>> >>> Hi Chao, >>> >>> Thank you for the suggestion. >>> I will add this to sanity_check_inode and remove it >>> from f2fs_lookup as it becomes redundant since f2fs_lookup >>> obtains the inode through f2fs_iget. For f2fs_unlink I will >>> move the i_nlink == 1 check to f2fs_rmdir. >> >> Hi Nikola, >> >> I meant we can move the i_nlink == 1 check from both f2fs_lookup() and >> f2fs_unlink() to sanity_check_inode(), because before we create in-memory >> inode, we will always call sanity_check_inode(). >> >> Let me know if you have other concerns. >> >> Thanks, >> > > The issue here is that sanity_check_inode will be called only when > we initially read the inode off disk, not when it's already in the cache > > The syzkaller repro does something like this: > Creates a directory structure /dir1/dir2 where dir1 has > i_nlink == 2, which is one less than it should. It then does > rmdir(/dir1/dir2) followed by rmdir(/dir1) which leads to the warning.
Oh, I missed this case. > > In such case what would you say should happen, should the second rmdir > fail and report the corruption, or do we close our eyes and just drop > i_nlink to 0 and possibly log a message that something isn't quite right? I agreed that we should keep i_nlink == 1 check in f2fs_unlink(). Thanks, > > Thank you, > >>> >>> I will send v2 as soon as I do some more testing. >> _______________________________________________ Linux-f2fs-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
