[PATCH] jfs: check agwidth before calculating the control page level

[Edward Adam Davis <eadavis@qq.com>]

The width in dmapctl of the AG is zero, it trigger a divide error when
calculating the control page level in dbAllocAG.

To avoid this issue, add a check for agwidth in dbAllocAG.

Reported-and-tested-by: syzbot+7c808908291a569281a9@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=7c808908291a569281a9
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
---
 fs/jfs/jfs_dmap.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
index f9009e4f9ffd..2377102d9c4c 100644
--- a/fs/jfs/jfs_dmap.c
+++ b/fs/jfs/jfs_dmap.c
@@ -1373,6 +1373,11 @@ dbAllocAG(struct bmap * bmp, int agno, s64 nblocks, int l2nb, s64 * results)
 		return (rc);
 	}
 
+	if (!bmp->db_agwidth) {
+		jfs_error(bmp->db_ipbmap->i_sb, "width in dmapctl of the AG is zero\n");
+		return -EIO;
+	}
+
 	/* the buffer for the dmap control page that fully describes the
 	 * allocation group.
 	 */
-- 
2.47.0