svcrdma: Use struct xdr_stream to decode ingress transport headers

The logic that checks incoming network headers has to be scrupulous.

De-duplicate: replace open-coded buffer overflow checks with the use
of xdr_stream helpers that are used most everywhere else XDR
decoding is done.

One minor change to the sanity checks: instead of checking the
length of individual segments, cap the length of the whole chunk
to be sure it can fit in the set of pages available in rq_pages.
This should be a better test of whether the server can handle the
chunks in each request.

Signed-off-by: Chuck Lever <[e-mail]>

include/linux/sunrpc/rpc_rdma.h

···
 enum {
 	rpcrdma_fixed_maxsz	= 4,
 	rpcrdma_segment_maxsz	= 4,
-	rpcrdma_readchunk_maxsz	= 2 + rpcrdma_segment_maxsz,
+	rpcrdma_readseg_maxsz	= 1 + rpcrdma_segment_maxsz,
+	rpcrdma_readchunk_maxsz	= 1 + rpcrdma_readseg_maxsz,
 };
 
 /*

include/linux/sunrpc/svc_rdma.h

···
 	struct ib_sge		rc_recv_sge;
 	void			*rc_recv_buf;
 	struct xdr_buf		rc_arg;
+	struct xdr_stream	rc_stream;
 	bool			rc_temp;
 	u32			rc_byte_len;
 	unsigned int		rc_page_count;

include/trace/events/rpcrdma.h

···
 );
 
 #define DEFINE_SEGMENT_EVENT(name)					\
-		DEFINE_EVENT(svcrdma_segment_event, svcrdma_encode_##name,\
+		DEFINE_EVENT(svcrdma_segment_event, svcrdma_##name,\
 				TP_PROTO(				\
 					u32 handle,			\
 					u32 length,			\
···
 				),					\
 				TP_ARGS(handle, length, offset))
 
-DEFINE_SEGMENT_EVENT(rseg);
-DEFINE_SEGMENT_EVENT(wseg);
+DEFINE_SEGMENT_EVENT(decode_wseg);
+DEFINE_SEGMENT_EVENT(encode_rseg);
+DEFINE_SEGMENT_EVENT(encode_wseg);
 
 DECLARE_EVENT_CLASS(svcrdma_chunk_event,
 	TP_PROTO(

net/sunrpc/xprtrdma/svc_rdma_recvfrom.c

···
 	arg->len = ctxt->rc_byte_len;
 }
 
-/* This accommodates the largest possible Write chunk,
- * in one segment.
+/* This accommodates the largest possible Write chunk.
  */
-#define MAX_BYTES_WRITE_SEG	((u32)(RPCSVC_MAXPAGES << PAGE_SHIFT))
+#define MAX_BYTES_WRITE_CHUNK ((u32)(RPCSVC_MAXPAGES << PAGE_SHIFT))
 
 /* This accommodates the largest possible Position-Zero
- * Read chunk or Reply chunk, in one segment.
+ * Read chunk or Reply chunk.
  */
-#define MAX_BYTES_SPECIAL_SEG	((u32)((RPCSVC_MAXPAGES + 2) << PAGE_SHIFT))
+#define MAX_BYTES_SPECIAL_CHUNK ((u32)((RPCSVC_MAXPAGES + 2) << PAGE_SHIFT))
 
 /* Sanity check the Read list.
  *
···
  * - This implementation supports only one Read chunk.
  *
  * Sanity checks:
- * - Read list does not overflow buffer.
+ * - Read list does not overflow Receive buffer.
  * - Segment size limited by largest NFS data payload.
  *
  * The segment count is limited to how many segments can
···
  * buffer. That's about 40 Read segments for a 1KB inline
  * threshold.
  *
- * Returns pointer to the following Write list.
+ * Return values:
+ *       %true: Read list is valid. @rctxt's xdr_stream is updated
+ *		to point to the first byte past the Read list.
+ *      %false: Read list is corrupt. @rctxt's xdr_stream is left
+ *		in an unknown state.
  */
-static __be32 *xdr_check_read_list(__be32 *p, const __be32 *end)
+static bool xdr_check_read_list(struct svc_rdma_recv_ctxt *rctxt)
 {
-	u32 position;
+	u32 position, len;
 	bool first;
+	__be32 *p;
 
+	p = xdr_inline_decode(&rctxt->rc_stream, sizeof(*p));
+	if (!p)
+		return false;
+
+	len = 0;
 	first = true;
-	while (*p++ != xdr_zero) {
-		if (first) {
-			position = be32_to_cpup(p++);
-			first = false;
-		} else if (be32_to_cpup(p++) != position) {
-			return NULL;
-		}
-		p++;	/* handle */
-		if (be32_to_cpup(p++) > MAX_BYTES_SPECIAL_SEG)
-			return NULL;
-		p += 2;	/* offset */
+	while (*p != xdr_zero) {
+		p = xdr_inline_decode(&rctxt->rc_stream,
+				      rpcrdma_readseg_maxsz * sizeof(*p));
+		if (!p)
+			return false;
 
-		if (p > end)
-			return NULL;
+		if (first) {
+			position = be32_to_cpup(p);
+			first = false;
+		} else if (be32_to_cpup(p) != position) {
+			return false;
+		}
+		p += 2;
+		len += be32_to_cpup(p);
+
+		p = xdr_inline_decode(&rctxt->rc_stream, sizeof(*p));
+		if (!p)
+			return false;
 	}
-	return p;
+	return len <= MAX_BYTES_SPECIAL_CHUNK;
 }
 
 /* The segment count is limited to how many segments can
···
  * buffer. That's about 60 Write segments for a 1KB inline
  * threshold.
  */
-static __be32 *xdr_check_write_chunk(__be32 *p, const __be32 *end,
-				     u32 maxlen)
+static bool xdr_check_write_chunk(struct svc_rdma_recv_ctxt *rctxt, u32 maxlen)
 {
-	u32 i, segcount;
+	u32 i, segcount, total;
+	__be32 *p;
 
-	segcount = be32_to_cpup(p++);
+	p = xdr_inline_decode(&rctxt->rc_stream, sizeof(*p));
+	if (!p)
+		return false;
+	segcount = be32_to_cpup(p);
+
+	total = 0;
 	for (i = 0; i < segcount; i++) {
-		p++;	/* handle */
-		if (be32_to_cpup(p++) > maxlen)
-			return NULL;
-		p += 2;	/* offset */
+		u32 handle, length;
+		u64 offset;
 
-		if (p > end)
-			return NULL;
+		p = xdr_inline_decode(&rctxt->rc_stream,
+				      rpcrdma_segment_maxsz * sizeof(*p));
+		if (!p)
+			return false;
+
+		handle = be32_to_cpup(p++);
+		length = be32_to_cpup(p++);
+		xdr_decode_hyper(p, &offset);
+		trace_svcrdma_decode_wseg(handle, length, offset);
+
+		total += length;
 	}
-
-	return p;
+	return total <= maxlen;
 }
 
 /* Sanity check the Write list.
  *
  * Implementation limits:
- * - This implementation supports only one Write chunk.
+ * - This implementation currently supports only one Write chunk.
  *
  * Sanity checks:
- * - Write list does not overflow buffer.
- * - Segment size limited by largest NFS data payload.
+ * - Write list does not overflow Receive buffer.
+ * - Chunk size limited by largest NFS data payload.
  *
- * Returns pointer to the following Reply chunk.
+ * Return values:
+ *       %true: Write list is valid. @rctxt's xdr_stream is updated
+ *		to point to the first byte past the Write list.
+ *      %false: Write list is corrupt. @rctxt's xdr_stream is left
+ *		in an unknown state.
  */
-static __be32 *xdr_check_write_list(__be32 *p, const __be32 *end)
+static bool xdr_check_write_list(struct svc_rdma_recv_ctxt *rctxt)
 {
-	u32 chcount;
+	u32 chcount = 0;
+	__be32 *p;
 
-	chcount = 0;
-	while (*p++ != xdr_zero) {
-		p = xdr_check_write_chunk(p, end, MAX_BYTES_WRITE_SEG);
+	p = xdr_inline_decode(&rctxt->rc_stream, sizeof(*p));
+	if (!p)
+		return false;
+	while (*p != xdr_zero) {
+		if (!xdr_check_write_chunk(rctxt, MAX_BYTES_WRITE_CHUNK))
+			return false;
+		++chcount;
+		p = xdr_inline_decode(&rctxt->rc_stream, sizeof(*p));
 		if (!p)
-			return NULL;
-		if (chcount++ > 1)
-			return NULL;
+			return false;
 	}
-	return p;
+	return chcount < 2;
 }
 
 /* Sanity check the Reply chunk.
  *
  * Sanity checks:
- * - Reply chunk does not overflow buffer.
- * - Segment size limited by largest NFS data payload.
+ * - Reply chunk does not overflow Receive buffer.
+ * - Chunk size limited by largest NFS data payload.
  *
- * Returns pointer to the following RPC header.
+ * Return values:
+ *       %true: Reply chunk is valid. @rctxt's xdr_stream is updated
+ *		to point to the first byte past the Reply chunk.
+ *      %false: Reply chunk is corrupt. @rctxt's xdr_stream is left
+ *		in an unknown state.
  */
-static __be32 *xdr_check_reply_chunk(__be32 *p, const __be32 *end)
+static bool xdr_check_reply_chunk(struct svc_rdma_recv_ctxt *rctxt)
 {
-	if (*p++ != xdr_zero) {
-		p = xdr_check_write_chunk(p, end, MAX_BYTES_SPECIAL_SEG);
-		if (!p)
-			return NULL;
-	}
-	return p;
+	__be32 *p;
+
+	p = xdr_inline_decode(&rctxt->rc_stream, sizeof(*p));
+	if (!p)
+		return false;
+	if (*p != xdr_zero)
+		if (!xdr_check_write_chunk(rctxt, MAX_BYTES_SPECIAL_CHUNK))
+			return false;
+	return true;
 }
 
 /* RPC-over-RDMA Version One private extension: Remote Invalidation.
···
 	ctxt->rc_inv_rkey = be32_to_cpu(inv_rkey);
 }
 
-/* On entry, xdr->head[0].iov_base points to first byte in the
- * RPC-over-RDMA header.
+/**
+ * svc_rdma_xdr_decode_req - Decode the transport header
+ * @rq_arg: xdr_buf containing ingress RPC/RDMA message
+ * @rctxt: state of decoding
+ *
+ * On entry, xdr->head[0].iov_base points to first byte of the
+ * RPC-over-RDMA transport header.
  *
  * On successful exit, head[0] points to first byte past the
  * RPC-over-RDMA header. For RDMA_MSG, this is the RPC message.
+ *
  * The length of the RPC-over-RDMA header is returned.
  *
  * Assumptions:
  * - The transport header is entirely contained in the head iovec.
  */
-static int svc_rdma_xdr_decode_req(struct xdr_buf *rq_arg)
+static int svc_rdma_xdr_decode_req(struct xdr_buf *rq_arg,
+				   struct svc_rdma_recv_ctxt *rctxt)
 {
-	__be32 *p, *end, *rdma_argp;
+	__be32 *p, *rdma_argp;
 	unsigned int hdr_len;
 
-	/* Verify that there's enough bytes for header + something */
-	if (rq_arg->len <= RPCRDMA_HDRLEN_ERR)
-		goto out_short;
-
 	rdma_argp = rq_arg->head[0].iov_base;
-	if (*(rdma_argp + 1) != rpcrdma_version)
-		goto out_version;
+	xdr_init_decode(&rctxt->rc_stream, rq_arg, rdma_argp, NULL);
 
-	switch (*(rdma_argp + 3)) {
+	p = xdr_inline_decode(&rctxt->rc_stream,
+			      rpcrdma_fixed_maxsz * sizeof(*p));
+	if (unlikely(!p))
+		goto out_short;
+	p++;
+	if (*p != rpcrdma_version)
+		goto out_version;
+	p += 2;
+	switch (*p) {
 	case rdma_msg:
 		break;
 	case rdma_nomsg:
 		break;
-
 	case rdma_done:
 		goto out_drop;
-
 	case rdma_error:
 		goto out_drop;
-
 	default:
 		goto out_proc;
 	}
 
-	end = (__be32 *)((unsigned long)rdma_argp + rq_arg->len);
-	p = xdr_check_read_list(rdma_argp + 4, end);
-	if (!p)
+	if (!xdr_check_read_list(rctxt))
 		goto out_inval;
-	p = xdr_check_write_list(p, end);
-	if (!p)
+	if (!xdr_check_write_list(rctxt))
 		goto out_inval;
-	p = xdr_check_reply_chunk(p, end);
-	if (!p)
-		goto out_inval;
-	if (p > end)
+	if (!xdr_check_reply_chunk(rctxt))
 		goto out_inval;
 
-	rq_arg->head[0].iov_base = p;
-	hdr_len = (unsigned long)p - (unsigned long)rdma_argp;
+	rq_arg->head[0].iov_base = rctxt->rc_stream.p;
+	hdr_len = xdr_stream_pos(&rctxt->rc_stream);
 	rq_arg->head[0].iov_len -= hdr_len;
 	rq_arg->len -= hdr_len;
 	trace_svcrdma_decode_rqst(rdma_argp, hdr_len);
···
 	rqstp->rq_next_page = rqstp->rq_respages;
 
 	p = (__be32 *)rqstp->rq_arg.head[0].iov_base;
-	ret = svc_rdma_xdr_decode_req(&rqstp->rq_arg);
+	ret = svc_rdma_xdr_decode_req(&rqstp->rq_arg, ctxt);
 	if (ret < 0)
 		goto out_err;
 	if (ret == 0)