[PATCH v2 05/19] svcrdma: Improve Read chunk sanity checking

Chuck Lever
2017-06-16T15:21:01Z

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

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

- Ensure that segment lengths are not crazy.

- Remove the segment count check. With a 1KB inline threshold, the
largest number of Read segments that can be conveyed is about 40
(for a RDMA_NOMSG Call message). This is nowhere near
RPCSVC_MAXPAGES. As far as I can tell, that was just a sanity
check and does not enforce an implementation limit.

Signed-off-by: Chuck Lever <chuck.lever-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
---
net/sunrpc/xprtrdma/svc_rdma_recvfrom.c | 55 +++++++++++++++++++++----------
1 file changed, 37 insertions(+), 18 deletions(-)

diff --git a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
index 55ad335..885ad95 100644
--- a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
+++ b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
@@ -117,15 +117,47 @@ static void rdma_build_arg_xdr(struct svc_rqst *rqstp,
rqstp->rq_arg.tail[0].iov_len = 0;
}

-static __be32 *xdr_check_read_list(__be32 *p, __be32 *end)
+/* This accommodates the largest possible Position-Zero
+ * Read chunk or Reply chunk, in one segment.
+ */
+#define MAX_BYTES_SPECIAL_SEG ((u32)((RPCSVC_MAXPAGES + 2) << PAGE_SHIFT))
+
+/* Sanity check the Read list.
+ *
+ * Implementation limits:
+ * - This implementation supports only one Read chunk.
+ *
+ * Sanity checks:
+ * - Read list does not overflow buffer.
+ * - Segment size limited by largest NFS data payload.
+ *
+ * The segment count is limited to how many segments can
+ * fit in the transport header without overflowing the
+ * buffer. That's about 40 Read segments for a 1KB inline
+ * threshold.
+ *
+ * Returns pointer to the following Write list.
+ */
+static __be32 *xdr_check_read_list(__be32 *p, const __be32 *end)
{
- __be32 *next;
+ u32 position;
+ bool first;

+ first = true;
while (*p++ != xdr_zero) {
- next = p + rpcrdma_readchunk_maxsz - 1;
- if (next > end)
+ 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 */
+
+ if (p > end)
return NULL;
- p = next;
}
return p;
}
@@ -478,16 +510,6 @@ int rdma_read_chunk_frmr(struct svcxprt_rdma *xprt,
return ret;
}

-static unsigned int
-rdma_rcl_chunk_count(struct rpcrdma_read_chunk *ch)
-{
- unsigned int count;
-
- for (count = 0; ch->rc_discrim != xdr_zero; ch++)
- count++;
- return count;
-}
-
/* If there was additional inline content, append it to the end of arg.pages.
* Tail copy has to be done after the reader function has determined how many
* pages are needed for RDMA READ.
@@ -567,9 +589,6 @@ static int rdma_read_chunks(struct svcxprt_rdma *xprt,
if (!ch)
return 0;

- if (rdma_rcl_chunk_count(ch) > RPCSVC_MAXPAGES)
- return -EINVAL;
-
/* The request is completed when the RDMA_READs complete. The
* head context keeps all the pages that comprise the
* request.