Re: [PATCH v4] f2fs: add check for deleted inode

[Chao Yu <chao@kernel.org>]

On 2/14/25 01:38, Jaegeuk Kim wrote:
> On 02/13, Chao Yu wrote:
>> On 2/13/25 00:47, Jaegeuk Kim wrote:
>>> On 02/12, Chao Yu wrote:
>>>> From: Leo Stone <leocstone@gmail.com>
>>>>
>>>> The syzbot reproducer mounts a f2fs image, then tries to unlink an
>>>> existing file. However, the unlinked file already has a link count of 0
>>>> when it is read for the first time in do_read_inode().
>>>>
>>>> Add a check to sanity_check_inode() for i_nlink == 0.
>>>>
>>>> [Chao Yu: rebase the code and fix orphan inode recovery issue]
>>>> Reported-by: syzbot+b01a36acd7007e273a83@syzkaller.appspotmail.com
>>>> Closes: https://syzkaller.appspot.com/bug?extid=b01a36acd7007e273a83
>>>> Fixes: 39a53e0ce0df ("f2fs: add superblock and major in-memory structure")
>>>> Signed-off-by: Leo Stone <leocstone@gmail.com>
>>>> Signed-off-by: Chao Yu <chao@kernel.org>
>>>> ---
>>>>  fs/f2fs/checkpoint.c | 4 ++++
>>>>  fs/f2fs/f2fs.h       | 1 +
>>>>  fs/f2fs/inode.c      | 6 ++++++
>>>>  3 files changed, 11 insertions(+)
>>>>
>>>> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
>>>> index bd890738b94d..ada2c548645c 100644
>>>> --- a/fs/f2fs/checkpoint.c
>>>> +++ b/fs/f2fs/checkpoint.c
>>>> @@ -751,6 +751,8 @@ int f2fs_recover_orphan_inodes(struct f2fs_sb_info *sbi)
>>>>  	if (is_sbi_flag_set(sbi, SBI_IS_WRITABLE))
>>>>  		f2fs_info(sbi, "orphan cleanup on readonly fs");
>>>>  
>>>> +	set_sbi_flag(sbi, SBI_ORPHAN_RECOVERY);
>>>
>>> What about using SBI_POR_DOING?
>>
>> SBI_POR_DOING will cover most flow of f2fs_fill_super(), I think we can add a
>> separated flag just covering f2fs_recover_orphan_inodes(), so that we can allow
>> iget() of root_inode and all inodes during roll-forward recovery to do sanity
>> check nlink w/ zero. What do you think?
> 
> Can we do this sanity check after f2fs_iget in the f2fs_unlink() only?

Sure, we need to cover f2fs_rename() as well, please check this:

https://lore.kernel.org/all/67450f9a.050a0220.21d33d.0003.GAE@google.com

Thanks,

> 
>>
>> Thanks,
>>
>>>
>>>> +
>>>>  	start_blk = __start_cp_addr(sbi) + 1 + __cp_payload(sbi);
>>>>  	orphan_blocks = __start_sum_addr(sbi) - 1 - __cp_payload(sbi);
>>>>  
>>>> @@ -778,9 +780,11 @@ int f2fs_recover_orphan_inodes(struct f2fs_sb_info *sbi)
>>>>  		}
>>>>  		f2fs_put_page(page, 1);
>>>>  	}
>>>> +
>>>>  	/* clear Orphan Flag */
>>>>  	clear_ckpt_flags(sbi, CP_ORPHAN_PRESENT_FLAG);
>>>>  out:
>>>> +	clear_sbi_flag(sbi, SBI_ORPHAN_RECOVERY);
>>>>  	set_sbi_flag(sbi, SBI_IS_RECOVERED);
>>>>  
>>>>  	return err;
>>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>>> index 05879c6dc4d6..1c75081c0c14 100644
>>>> --- a/fs/f2fs/f2fs.h
>>>> +++ b/fs/f2fs/f2fs.h
>>>> @@ -1322,6 +1322,7 @@ enum {
>>>>  	SBI_IS_CLOSE,				/* specify unmounting */
>>>>  	SBI_NEED_FSCK,				/* need fsck.f2fs to fix */
>>>>  	SBI_POR_DOING,				/* recovery is doing or not */
>>>> +	SBI_ORPHAN_RECOVERY,			/* orphan inodes recovery is doing */
>>>>  	SBI_NEED_SB_WRITE,			/* need to recover superblock */
>>>>  	SBI_NEED_CP,				/* need to checkpoint */
>>>>  	SBI_IS_SHUTDOWN,			/* shutdown by ioctl */
>>>> diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
>>>> index d6ad7810df69..02f1b69d03d8 100644
>>>> --- a/fs/f2fs/inode.c
>>>> +++ b/fs/f2fs/inode.c
>>>> @@ -386,6 +386,12 @@ static bool sanity_check_inode(struct inode *inode, struct page *node_page)
>>>>  		}
>>>>  	}
>>>>  
>>>> +	if (inode->i_nlink == 0 && !is_sbi_flag_set(sbi, SBI_ORPHAN_RECOVERY)) {
>>>> +		f2fs_warn(sbi, "%s: inode (ino=%lx) has a link count of 0",
>>>> +			  __func__, inode->i_ino);
>>>> +		return false;
>>>> +	}
>>>> +
>>>>  	return true;
>>>>  }
>>>>  
>>>> -- 
>>>> 2.48.1.502.g6dc24dfdaf-goog