Re: [PATCH] xfs_db: make sure agblocks is valid to prevent corruption

["Darrick J. Wong" <djwong@kernel.org>]

On Wed, Aug 21, 2024 at 06:44:12PM +0800, liuhuan01@kylinos.cn wrote:
> From: liuh <liuhuan01@kylinos.cn>
> 
> Recently, I was testing xfstests. When I run xfs/350 case, it always generate coredump during the process.
> 	xfs_db -c "sb 0" -c "p agblocks" /dev/loop1
> 
> System will generate signal SIGFPE corrupt the process. And the stack as follow:
> corrupt at: (*bpp)->b_pag = xfs_perag_get(btp->bt_mount, xfs_daddr_to_agno(btp->bt_mount, blkno)); in function libxfs_getbuf_flags
> 	#0  libxfs_getbuf_flags
> 	#1  libxfs_getbuf_flags
> 	#2  libxfs_buf_read_map
> 	#3  libxfs_buf_read
> 	#4  libxfs_mount
> 	#5  init
> 	#6  main
> 
> The coredump was caused by the corrupt superblock metadata: (mp)->m_sb.sb_agblocks, it was 0.
> In this case, user cannot run in expert mode also.
> 
> Never check (mp)->m_sb.sb_agblocks before use it cause this issue.
> Make sure (mp)->m_sb.sb_agblocks > 0 before libxfs_mount to prevent corruption and leave a message.
> 
> Signed-off-by: liuh <liuhuan01@kylinos.cn>
> ---
>  db/init.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/db/init.c b/db/init.c
> index cea25ae5..2d3295ba 100644
> --- a/db/init.c
> +++ b/db/init.c
> @@ -129,6 +129,13 @@ init(
>  		}
>  	}
>  
> +	if (unlikely(sbp->sb_agblocks == 0)) {
> +		fprintf(stderr,
> +			_("%s: device %s agblocks unexpected\n"),
> +			progname, x.data.name);
> +		exit(1);

What if we set sb_agblocks to 1 and let the debugger continue?

--D

> +	}
> +
>  	agcount = sbp->sb_agcount;
>  	mp = libxfs_mount(&xmount, sbp, &x, LIBXFS_MOUNT_DEBUGGER);
>  	if (!mp) {
> -- 
> 2.43.0
>