Re: [PATCH] nilfs2: handle corrupted checkpoint count gracefully during deletion

[Viacheslav Dubeyko]

On Tue, 2026-07-07 at 16:59 +0900, Ryusuke Konishi wrote:
> From: Igor Putko <igorpetindev@xxxxxxxxx>
> 
> Syzkaller reported a kernel warning in
> nilfs_cpfile_delete_checkpoints()
> due to a corrupted checkpoint count on the storage medium where
> le32_to_cpu(cp->cp_checkpoints_count) is less than the number of
> checkpoints being deleted.
> Triggering a WARN_ON() for disk image corruption is suboptimal. Fix
> this by returning -EIO and reporting a filesystem error via
> nilfs_error() instead of interrupting execution with a kernel
> warning.
> 
> Reported-by: syzbot+79b815da3aec0a6a4d02@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=79b815da3aec0a6a4d02
> Signed-off-by: Igor Putko <igorpetindev@xxxxxxxxx>
> Fixes: 1f5abe7e7dbc ("nilfs2: replace BUG_ON and BUG calls
> triggerable from ioctl")
> Cc: <stable+noautosel@xxxxxxxxxx> # Warning suppression primarily;
> will request backport individually if needed
> Signed-off-by: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx>
> ---
> Hi Viacheslav,
> 
> Please apply this for the next cycle.
> 
> This fixes a kernel warning and a missed inconsistency check that
> could
> occur with file system images containing corrupted checkpoint
> metadata.
> 
> Thanks,
> Ryusuke Konishi
> 
>  fs/nilfs2/cpfile.c | 20 ++++++++++++++++----
>  1 file changed, 16 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/nilfs2/cpfile.c b/fs/nilfs2/cpfile.c
> index 4bbdc832d7f2..d3349fa58abe 100644
> --- a/fs/nilfs2/cpfile.c
> +++ b/fs/nilfs2/cpfile.c
> @@ -81,18 +81,26 @@ nilfs_cpfile_block_add_valid_checkpoints(const
> struct inode *cpfile,
>  	return count;
>  }
>  
> -static unsigned int
> +static int
>  nilfs_cpfile_block_sub_valid_checkpoints(const struct inode *cpfile,
>  					 struct buffer_head *bh,
>  					 unsigned int n)
>  {
>  	struct nilfs_checkpoint *cp;
> -	unsigned int count;
> +	unsigned int checkpoints_count;
> +	int count;
>  
>  	cp = kmap_local_folio(bh->b_folio,
>  			      offset_in_folio(bh->b_folio, bh-
> >b_data));
> -	WARN_ON(le32_to_cpu(cp->cp_checkpoints_count) < n);
> -	count = le32_to_cpu(cp->cp_checkpoints_count) - n;
> +	checkpoints_count = le32_to_cpu(cp->cp_checkpoints_count);
> +	if (unlikely(checkpoints_count < n)) {
> +		nilfs_error(cpfile->i_sb,
> +			    "deleted checkpoints count %u exceeds
> block count %u",
> +			    n, checkpoints_count);
> +		kunmap_local(cp);
> +		return -EIO;
> +	}
> +	count = checkpoints_count - n;
>  	cp->cp_checkpoints_count = cpu_to_le32(count);
>  	kunmap_local(cp);
>  	return count;
> @@ -522,6 +530,10 @@ int nilfs_cpfile_delete_checkpoints(struct inode
> *cpfile,
>  		count =
> nilfs_cpfile_block_sub_valid_checkpoints(cpfile, cp_bh,
>  								
> nicps);
>  		brelse(cp_bh);
> +		if (unlikely(count < 0)) {
> +			ret = count;
> +			break;
> +		}
>  		if (count)
>  			continue;
>  

Applied.

Thanks,
Slava.