fs/jfs: Add validity check for db_maxag and db_agpref

[ Upstream commit 64933ab7b04881c6c18b21ff206c12278341c72e ]

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>
Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
index 3a18423..4d59373 100644 (file)
--- 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);