svcrdma: Prevent a UAF in svc_rdma_send()

In some error flow cases, svc_rdma_wc_send() releases @ctxt. Copy
the sc_cid field in @ctxt to a stack variable in order to guarantee
that the value is available after the ib_post_send() call.

In case the new comment looks a little strange, this will be done
with at least one more field in a subsequent patch.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

diff --git a/net/sunrpc/xprtrdma/svc_rdma_sendto.c b/net/sunrpc/xprtrdma/svc_rdma_sendto.c
index f1f5c7b58fce52f4a056d79c559a07c3e3bf4c93..b6fc9299b472d6cc6c15658835c008b465edbee7 100644 (file)
--- a/net/sunrpc/xprtrdma/svc_rdma_sendto.c
+++ b/net/sunrpc/xprtrdma/svc_rdma_sendto.c
@@ -316,12 +316,17 @@ flushed:
  * @rdma: transport on which to post the WR
  * @ctxt: send ctxt with a Send WR ready to post
  *
+ * Copy fields in @ctxt to stack variables in order to guarantee
+ * that these values remain available after the ib_post_send() call.
+ * In some error flow cases, svc_rdma_wc_send() releases @ctxt.
+ *
  * Returns zero if the Send WR was posted successfully. Otherwise, a
  * negative errno is returned.
  */
 int svc_rdma_send(struct svcxprt_rdma *rdma, struct svc_rdma_send_ctxt *ctxt)
 {
        struct ib_send_wr *wr = &ctxt->sc_send_wr;
+       struct rpc_rdma_cid cid = ctxt->sc_cid;
        int ret;
 
        might_sleep();
@@ -337,12 +342,12 @@ int svc_rdma_send(struct svcxprt_rdma *rdma, struct svc_rdma_send_ctxt *ctxt)
                if ((atomic_dec_return(&rdma->sc_sq_avail) < 0)) {
                        svc_rdma_wake_send_waiters(rdma, 1);
                        percpu_counter_inc(&svcrdma_stat_sq_starve);
-                       trace_svcrdma_sq_full(rdma, &ctxt->sc_cid);
+                       trace_svcrdma_sq_full(rdma, &cid);
                        wait_event(rdma->sc_send_wait,
                                   atomic_read(&rdma->sc_sq_avail) > 0);
                        if (test_bit(XPT_CLOSE, &rdma->sc_xprt.xpt_flags))
                                return -ENOTCONN;
-                       trace_svcrdma_sq_retry(rdma, &ctxt->sc_cid);
+                       trace_svcrdma_sq_retry(rdma, &cid);
                        continue;
                }
 
@@ -353,7 +358,7 @@ int svc_rdma_send(struct svcxprt_rdma *rdma, struct svc_rdma_send_ctxt *ctxt)
                return 0;
        }
 
-       trace_svcrdma_sq_post_err(rdma, &ctxt->sc_cid, ret);
+       trace_svcrdma_sq_post_err(rdma, &cid, ret);
        svc_xprt_deferred_close(&rdma->sc_xprt);
        svc_rdma_wake_send_waiters(rdma, 1);
        return ret;