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]
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>
---
- no logic change, just rebase the code to last dev-test branch
 fs/f2fs/inode.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
index d6ad7810df69..543fb942bec1 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) {
+		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

On 02/11, 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]
> 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>
> ---
> - no logic change, just rebase the code to last dev-test branch
>  fs/f2fs/inode.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
> index d6ad7810df69..543fb942bec1 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) {
> +		f2fs_warn(sbi, "%s: inode (ino=%lx) has a link count of 0",
> +			  __func__, inode->i_ino);
> +		return false;
> +	}

This gives a wrong EFSCORRUPTED when recoverying orphan inodes.

f2fs_recover_orphan_inodes
-> f2fs_iget_retry
 -> orphan inode can have i_nlink = 0.

> +
>  	return true;
>  }
>  
> -- 
> 2.48.1.502.g6dc24dfdaf-goog

On 2/12/25 11:24, Jaegeuk Kim wrote:
> On 02/11, 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]
>> 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>
>> ---
>> - no logic change, just rebase the code to last dev-test branch
>>  fs/f2fs/inode.c | 6 ++++++
>>  1 file changed, 6 insertions(+)
>>
>> diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
>> index d6ad7810df69..543fb942bec1 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) {
>> +		f2fs_warn(sbi, "%s: inode (ino=%lx) has a link count of 0",
>> +			  __func__, inode->i_ino);
>> +		return false;
>> +	}
> 
> This gives a wrong EFSCORRUPTED when recoverying orphan inodes.

Correct, I noticed that it may fail generic/417, let me fix this.

Thanks,

> 
> f2fs_recover_orphan_inodes
> -> f2fs_iget_retry
>  -> orphan inode can have i_nlink = 0.
> 
>> +
>>  	return true;
>>  }
>>  
>> -- 
>> 2.48.1.502.g6dc24dfdaf-goog