From: Chuck Lever <chuck.lever@xxxxxxxxxx>
Dan Carpenter reports:
> Commit 78147ca8b4a9 ("svcrdma: Add a "parsed chunk list" data
> structure") from Jun 22, 2020 (linux-next), leads to the following
> Smatch static checker warning:
>
> net/sunrpc/xprtrdma/svc_rdma_recvfrom.c:498 xdr_check_write_chunk()
> warn: potential user controlled sizeof overflow 'segcount * 4 * 4'
>
> net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> 488 static bool xdr_check_write_chunk(struct svc_rdma_recv_ctxt *rctxt)
> 489 {
> 490 u32 segcount;
> 491 __be32 *p;
> 492
> 493 if (xdr_stream_decode_u32(&rctxt->rc_stream, &segcount))
> ^^^^^^^^
>
> 494 return false;
> 495
> 496 /* A bogus segcount causes this buffer overflow check to fail. */
> 497 p = xdr_inline_decode(&rctxt->rc_stream,
> --> 498 segcount * rpcrdma_segment_maxsz * sizeof(*p));
>
>
> segcount is an untrusted u32. On 32bit systems anything >= SIZE_MAX / 16 will
> have an integer overflow and some those values will be accepted by
> xdr_inline_decode().
Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Fixes: 78147ca8b4a9 ("svcrdma: Add a "parsed chunk list" data structure")
Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
---
net/sunrpc/xprtrdma/svc_rdma_recvfrom.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
index d72953f29258..037c037fab88 100644
--- a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
+++ b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
@@ -493,7 +493,13 @@ static bool xdr_check_write_chunk(struct svc_rdma_recv_ctxt *rctxt)
if (xdr_stream_decode_u32(&rctxt->rc_stream, &segcount))
return false;
- /* A bogus segcount causes this buffer overflow check to fail. */
+ /* Before trusting the segcount value enough to perform
+ * computation with it, perform a simple range check. This
+ * is an arbitrary but sensible limit (ie, not architectural).
+ */
+ if (unlikely(segcount > RPCSVC_MAXPAGES))
+ return false;
+
p = xdr_inline_decode(&rctxt->rc_stream,
segcount * rpcrdma_segment_maxsz * sizeof(*p));
return p != NULL;
