Re: [PATCH] fs: jfs: fix shift-out-of-bounds in dbAllocAG

[Dave Kleikamp]

On 9/29/22 12:44AM, Dongliang Mu wrote:
> From: Dongliang Mu <mudongliangabcd@xxxxxxxxx>
>
> Syzbot found a crash : UBSAN: shift-out-of-bounds in dbAllocAG. The
> underlying bug is the missing check of bmp->db_agl2size. The field can
> be greater than 32 and trigger the shift-out-of-bounds.

The shift is done to a 64-byte value, not 32.

The volume can contain up to 2^43 blocks, which are divided up into 128 
(2^7) aggregate groups, so each AG can have 2^36 blocks, which makes 36 
a valid value for db_agl2size.

> Fix this bug by adding a check of bmp->db_agl2size in dbMount since this
> field is used in many following functions. Note that, for maintainance,
> I reorganzie the error handling code of dbMount.
>
> Reported-by: syzbot+15342c1aa6a00fb7a438@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Dongliang Mu <mudongliangabcd@xxxxxxxxx>
> ---
>   fs/jfs/jfs_dmap.c | 21 +++++++++++++++------
>   1 file changed, 15 insertions(+), 6 deletions(-)
>
> diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
> index 6b838d3ae7c2..4c717f245920 100644
> --- a/fs/jfs/jfs_dmap.c
> +++ b/fs/jfs/jfs_dmap.c
> @@ -155,7 +155,7 @@ int dbMount(struct inode *ipbmap)
>   	struct bmap *bmp;
>   	struct dbmap_disk *dbmp_le;
>   	struct metapage *mp;
> -	int i;
> +	int i, err;
>   
>   	/*
>   	 * allocate/initialize the in-memory bmap descriptor
> @@ -170,8 +170,8 @@ int dbMount(struct inode *ipbmap)
>   			   BMAPBLKNO << JFS_SBI(ipbmap->i_sb)->l2nbperpage,
>   			   PSIZE, 0);
>   	if (mp == NULL) {
> -		kfree(bmp);
> -		return -EIO;
> +		err = -EIO;
> +		goto err_kfree_bmp;
>   	}
>   
>   	/* copy the on-disk bmap descriptor to its in-memory version. */
> @@ -181,9 +181,8 @@ int dbMount(struct inode *ipbmap)
>   	bmp->db_l2nbperpage = le32_to_cpu(dbmp_le->dn_l2nbperpage);
>   	bmp->db_numag = le32_to_cpu(dbmp_le->dn_numag);
>   	if (!bmp->db_numag) {
> -		release_metapage(mp);
> -		kfree(bmp);
> -		return -EINVAL;
> +		err = -EINVAL;
> +		goto err_release_metapage;
>   	}
>   
>   	bmp->db_maxlevel = le32_to_cpu(dbmp_le->dn_maxlevel);
> @@ -194,6 +193,10 @@ int dbMount(struct inode *ipbmap)
>   	bmp->db_agwidth = le32_to_cpu(dbmp_le->dn_agwidth);
>   	bmp->db_agstart = le32_to_cpu(dbmp_le->dn_agstart);
>   	bmp->db_agl2size = le32_to_cpu(dbmp_le->dn_agl2size);
> +	if (bmp->db_agl2size >= 32) {

I think the right number here is MAXMAPSIZE - L2MAXAG, so

	if (bmp->db_agl2size > (MAXMAPSIZE - L2MAXAG)) {

> +		err = -EINVAL;
> +		goto err_release_metapage;
> +	}
>   	for (i = 0; i < MAXAG; i++)
>   		bmp->db_agfree[i] = le64_to_cpu(dbmp_le->dn_agfree[i]);
>   	bmp->db_agsize = le64_to_cpu(dbmp_le->dn_agsize);
> @@ -214,6 +217,12 @@ int dbMount(struct inode *ipbmap)
>   	BMAP_LOCK_INIT(bmp);
>   
>   	return (0);
> +
> +err_release_metapage:
> +	release_metapage(mp);
> +err_kfree_bmp:
> +	kfree(bmp);
> +	return err;
>   }
>   
>