jfs: array-index-out-of-bounds fix in dtReadFirst

The value of stbl can be sometimes out of bounds due
to a bad filesystem. Added a check with appopriate return
of error code in that case.

Reported-by: syzbot+65fa06e29859e41a83f3@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=65fa06e29859e41a83f3
Signed-off-by: Ghanshyam Agrawal <ghanshyam1898@gmail.com>
Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>

diff --git a/fs/jfs/jfs_dtree.c b/fs/jfs/jfs_dtree.c
index 5d3127ca68a42d76ac1d87b6ff6cee22d1b3b41d..69fd936fbdb37995a38c978f1bbb2f27d5df9112 100644 (file)
--- a/fs/jfs/jfs_dtree.c
+++ b/fs/jfs/jfs_dtree.c
@@ -3086,6 +3086,13 @@ static int dtReadFirst(struct inode *ip, struct btstack * btstack)
 
                /* get the leftmost entry */
                stbl = DT_GETSTBL(p);
+
+               if (stbl[0] < 0 || stbl[0] > 127) {
+                       DT_PUTPAGE(mp);
+                       jfs_error(ip->i_sb, "stbl[0] out of bound\n");
+                       return -EIO;
+               }
+
                xd = (pxd_t *) & p->slot[stbl[0]];
 
                /* get the child page block address */