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

The stbl might contain some invalid values. Added a check to
return error code in that case.

Reported-by: syzbot+0315f8fe99120601ba88@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=0315f8fe99120601ba88
Signed-off-by: Ghanshyam Agrawal <ghanshyam1898@gmail.com>
Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>

Author: ghanshyam1898

fs/jfs/jfs_dtree.c

@@ -2891,6 +2891,14 @@ int jfs_readdir(struct file *file, struct dir_context *ctx)
 		stbl = DT_GETSTBL(p);
 
 		for (i = index; i < p->header.nextindex; i++) {
+			if (stbl[i] < 0 || stbl[i] > 127) {
+				jfs_err("JFS: Invalid stbl[%d] = %d for inode %ld, block = %lld",
+					i, stbl[i], (long)ip->i_ino, (long long)bn);
+				free_page(dirent_buf);
+				DT_PUTPAGE(mp);
+				return -EIO;
+			}
+
 			d = (struct ldtentry *) & p->slot[stbl[i]];
 
 			if (((long) jfs_dirent + d->namlen + 1) >