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

[Jaegeuk Kim <jaegeuk@kernel.org>]

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?

> 
> 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