SUNRPC: Ensure xdr_buf_read_netobj() checks for memory overruns

Also clean up the code...
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

net/sunrpc/xdr.c

@@ -773,44 +773,37 @@ xdr_encode_word(struct xdr_buf *buf, unsigned int base, u32 obj)
  * entirely in the head or the tail, set object to point to it; otherwise
  * try to find space for it at the end of the tail, copy it there, and
  * set obj to point to it. */
-int
-xdr_buf_read_netobj(struct xdr_buf *buf, struct xdr_netobj *obj, unsigned int offset)
+int xdr_buf_read_netobj(struct xdr_buf *buf, struct xdr_netobj *obj, unsigned int offset)
 {
-	unsigned int tail_offset = buf->head[0].iov_len + buf->page_len;
-	unsigned int obj_end_offset;
+	struct xdr_buf subbuf;
 
 	if (xdr_decode_word(buf, offset, &obj->len))
-		goto out;
-	obj_end_offset = offset + 4 + obj->len;
-
-	if (obj_end_offset <= buf->head[0].iov_len) {
-		/* The obj is contained entirely in the head: */
-		obj->data = buf->head[0].iov_base + offset + 4;
-	} else if (offset + 4 >= tail_offset) {
-		if (obj_end_offset - tail_offset
-				> buf->tail[0].iov_len)
-			goto out;
-		/* The obj is contained entirely in the tail: */
-		obj->data = buf->tail[0].iov_base
-			+ offset - tail_offset + 4;
-	} else {
+		return -EFAULT;
+	if (xdr_buf_subsegment(buf, &subbuf, offset + 4, obj->len))
+		return -EFAULT;
+
+	/* Is the obj contained entirely in the head? */
+	obj->data = subbuf.head[0].iov_base;
+	if (subbuf.head[0].iov_len == obj->len)
+		return 0;
+	/* ..or is the obj contained entirely in the tail? */
+	obj->data = subbuf.tail[0].iov_base;
+	if (subbuf.tail[0].iov_len == obj->len)
+		return 0;
+
 	/* use end of tail as storage for obj:
 	 * (We don't copy to the beginning because then we'd have
 	 * to worry about doing a potentially overlapping copy.
 	 * This assumes the object is at most half the length of the
 	 * tail.) */
-		if (obj->len > buf->tail[0].iov_len)
-			goto out;
-		obj->data = buf->tail[0].iov_base + buf->tail[0].iov_len - 
-				obj->len;
-		if (read_bytes_from_xdr_buf(buf, offset + 4,
-					obj->data, obj->len))
-			goto out;
-
-	}
+	if (obj->len > buf->buflen - buf->len)
+		return -ENOMEM;
+	if (buf->tail[0].iov_len != 0)
+		obj->data = buf->tail[0].iov_base + buf->tail[0].iov_len;
+	else
+		obj->data = buf->head[0].iov_base + buf->head[0].iov_len;
+	__read_bytes_from_xdr_buf(&subbuf, obj->data, obj->len);
 	return 0;
-out:
-	return -1;
 }
 
 /* Returns 0 on success, or else a negative error code. */