[PATCH v2 06/19] svcrdma: Improve Write chunk sanity checking

Chuck Lever
2017-06-16T15:21:09Z

Identify malformed transport headers and unsupported chunk
combinations as early as possible.

- Reject RPC-over-RDMA messages that contain more than one Write
chunk, since this implementation does not support more than one per
message.

- Ensure that segment lengths are not crazy.

- Ensure that the chunk's segment count is not crazy.

With a 1KB inline threshold, the largest number of Write segments
that can be conveyed is about 60 (for a RDMA_NOMSG Reply message).

Signed-off-by: Chuck Lever <chuck.lever-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
---
net/sunrpc/xprtrdma/svc_rdma_recvfrom.c | 52 ++++++++++++++++++++++++++++---
1 file changed, 47 insertions(+), 5 deletions(-)

diff --git a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
index 885ad95..cf8be18 100644
--- a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
+++ b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
@@ -117,6 +117,11 @@ static void rdma_build_arg_xdr(struct svc_rqst *rqstp,
rqstp->rq_arg.tail[0].iov_len = 0;
}

+/* This accommodates the largest possible Write chunk,
+ * in one segment.
+ */
+#define MAX_BYTES_WRITE_SEG ((u32)(RPCSVC_MAXPAGES << PAGE_SHIFT))
+
/* This accommodates the largest possible Position-Zero
* Read chunk or Reply chunk, in one segment.
*/
@@ -162,15 +167,52 @@ static __be32 *xdr_check_read_list(__be32 *p, const __be32 *end)
return p;
}

-static __be32 *xdr_check_write_list(__be32 *p, __be32 *end)
+/* The segment count is limited to how many segments can
+ * fit in the transport header without overflowing the
+ * 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)
{
- __be32 *next;
+ u32 i, segcount;
+
+ segcount = be32_to_cpup(p++);
+ for (i = 0; i < segcount; i++) {
+ p++; /* handle */
+ if (be32_to_cpup(p++) > maxlen)
+ return NULL;
+ p += 2; /* offset */
+
+ if (p > end)
+ return NULL;
+ }
+
+ return p;
+}

+/* Sanity check the Write list.
+ *
+ * Implementation limits:
+ * - This implementation supports only one Write chunk.
+ *
+ * Sanity checks:
+ * - Write list does not overflow buffer.
+ * - Segment size limited by largest NFS data payload.
+ *
+ * Returns pointer to the following Reply chunk.
+ */
+static __be32 *xdr_check_write_list(__be32 *p, const __be32 *end)
+{
+ u32 chcount;
+
+ chcount = 0;
while (*p++ != xdr_zero) {
- next = p + 1 + be32_to_cpup(p) * rpcrdma_segment_maxsz;
- if (next > end)
+ p = xdr_check_write_chunk(p, end, MAX_BYTES_WRITE_SEG);
+ if (!p)
+ return NULL;
+ if (chcount++ > 1)
return NULL;
- p = next;
}
return p;
}