Re: [PATCH v3] ocfs2: Invalidate inode if i_mode is zero after block read

[Joseph Qi <joseph.qi@linux.alibaba.com>]

On 2025/11/20 10:32, Heming Zhao wrote:
> On Thu, Nov 20, 2025 at 01:17:24AM +0300, Ahmet Eray Karadag wrote:
>> A panic occurs in ocfs2_unlink due to WARN_ON(inode->i_nlink == 0) when
>> handling a corrupted inode with i_mode=0 and i_nlink=0 in memory.
>>
>> This "zombie" inode is created because ocfs2_read_locked_inode proceeds
>> even after ocfs2_validate_inode_block successfully validates a block
>> that structurally looks okay (passes checksum, signature etc.) but
>> contains semantically invalid data (specifically i_mode=0). The current
>> validation function doesn't check for i_mode being zero.
>>
>> This results in an in-memory inode with i_mode=0 being added to the VFS
>> cache, which later triggers the panic during unlink.
>>
>> Prevent this by adding an explicit check for (i_mode == 0, i_nlink == 0, non-orphan)
>> within ocfs2_validate_inode_block. If the check is true, return -EFSCORRUPTED to signal
>> corruption. This causes the caller (ocfs2_read_locked_inode) to invoke
>> make_bad_inode(), correctly preventing the zombie inode from entering
>> the cache.
>>
>> Reported-by: syzbot+55c40ae8a0e5f3659f2b@syzkaller.appspotmail.com
>> Fixes: https://syzkaller.appspot.com/bug?extid=55c40ae8a0e5f3659f2b
>> Co-developed-by: Albin Babu Varghese <albinbabuvarghese20@gmail.com>
>> Signed-off-by: Albin Babu Varghese <albinbabuvarghese20@gmail.com>
>> Signed-off-by: Ahmet Eray Karadag <eraykrdg1@gmail.com>
>> Previous link: https://lore.kernel.org/all/20251022222752.46758-2-eraykrdg1@gmail.com/T/
>> ---
>> v2:
>>  - Only checking either i_links_count == 0 or i_mode == 0
>>  - Not performing le16_to_cpu() anymore
>>  - Tested with ocfs2-test
>> ---
>> v3:
>>  - Add checking both high and low bits of i_links_count
>> ---
>>  fs/ocfs2/inode.c | 7 +++++++
>>  1 file changed, 7 insertions(+)
>>
>> diff --git a/fs/ocfs2/inode.c b/fs/ocfs2/inode.c
>> index 14bf440ea4df..c8b129db756e 100644
>> --- a/fs/ocfs2/inode.c
>> +++ b/fs/ocfs2/inode.c
>> @@ -1456,6 +1456,13 @@ int ocfs2_validate_inode_block(struct super_block *sb,
>>  		goto bail;
>>  	}
>>  
>> +	if (!ocfs2_read_links_count(di) || !di->i_mode) {
> 
> the code logic looks good to me, but I prefer the following code to save a few
> cpu cycles.
> 
> ```
> /* only check if the "link count" or i_mode is ZERO */
> if (!(di->i_links_count | di->i_links_count_hi) || !di->i_mode)
> ```
> 
> @Joseph
> which do you like?
> 
Sorry to miss this thread discuss.
The above check looks wried since "(di->i_links_count|di->i_links_count_hi)"
is meaningless, though it may work well...
So I'd prefer the code readability first.

BTW, from the syzbot report, I haven't seen where to show i_mode=0 or
i_nlink=0. Am I missing something?

Thanks,
Joseph