Both db_maxag and db_agpref are used as the index of the
db_agfree array, but there is currently no validity check for
db_maxag and db_agpref, which can lead to errors.

The following is related bug reported by Syzbot:

UBSAN: array-index-out-of-bounds in fs/jfs/jfs_dmap.c:639:20
index 7936 is out of range for type 'atomic_t[128]'

Add checking that the values of db_maxag and db_agpref are valid
indexes for the db_agfree array.

Reported-by: syzbot+38e876a8aa44b7115c76@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=38e876a8aa44b7115c76
Signed-off-by: Juntong Deng <juntong.deng@outlook.com>
---
 fs/jfs/jfs_dmap.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
index 3a1842348112..4d59373f9e6c 100644
--- a/fs/jfs/jfs_dmap.c
+++ b/fs/jfs/jfs_dmap.c
@@ -195,6 +195,12 @@ int dbMount(struct inode *ipbmap)
 	bmp->db_maxlevel = le32_to_cpu(dbmp_le->dn_maxlevel);
 	bmp->db_maxag = le32_to_cpu(dbmp_le->dn_maxag);
 	bmp->db_agpref = le32_to_cpu(dbmp_le->dn_agpref);
+	if (bmp->db_maxag >= MAXAG || bmp->db_maxag < 0 ||
+		bmp->db_agpref >= MAXAG || bmp->db_agpref < 0) {
+		err = -EINVAL;
+		goto err_release_metapage;
+	}
+
 	bmp->db_aglevel = le32_to_cpu(dbmp_le->dn_aglevel);
 	bmp->db_agheight = le32_to_cpu(dbmp_le->dn_agheight);
 	bmp->db_agwidth = le32_to_cpu(dbmp_le->dn_agwidth);
-- 
2.39.2

On 10/3/23 1:06PM, Juntong Deng wrote:
> Both db_maxag and db_agpref are used as the index of the
> db_agfree array, but there is currently no validity check for
> db_maxag and db_agpref, which can lead to errors.
> 
> The following is related bug reported by Syzbot:
> 
> UBSAN: array-index-out-of-bounds in fs/jfs/jfs_dmap.c:639:20
> index 7936 is out of range for type 'atomic_t[128]'
> 
> Add checking that the values of db_maxag and db_agpref are valid
> indexes for the db_agfree array.

Looks good. Applied.

Thanks,
Shaggy

> 
> Reported-by: syzbot+38e876a8aa44b7115c76@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=38e876a8aa44b7115c76
> Signed-off-by: Juntong Deng <juntong.deng@outlook.com>
> ---
>   fs/jfs/jfs_dmap.c | 6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
> index 3a1842348112..4d59373f9e6c 100644
> --- a/fs/jfs/jfs_dmap.c
> +++ b/fs/jfs/jfs_dmap.c
> @@ -195,6 +195,12 @@ int dbMount(struct inode *ipbmap)
>   	bmp->db_maxlevel = le32_to_cpu(dbmp_le->dn_maxlevel);
>   	bmp->db_maxag = le32_to_cpu(dbmp_le->dn_maxag);
>   	bmp->db_agpref = le32_to_cpu(dbmp_le->dn_agpref);
> +	if (bmp->db_maxag >= MAXAG || bmp->db_maxag < 0 ||
> +		bmp->db_agpref >= MAXAG || bmp->db_agpref < 0) {
> +		err = -EINVAL;
> +		goto err_release_metapage;
> +	}
> +
>   	bmp->db_aglevel = le32_to_cpu(dbmp_le->dn_aglevel);
>   	bmp->db_agheight = le32_to_cpu(dbmp_le->dn_agheight);
>   	bmp->db_agwidth = le32_to_cpu(dbmp_le->dn_agwidth);