CVE-2016-4429: sunrpc: Do not use alloca in clntudp_call [BZ #20112]

The call is technically in a loop, and under certain circumstances
(which are quite difficult to reproduce in a test case), alloca
can be invoked repeatedly during a single call to clntudp_call.
As a result, the available stack space can be exhausted (even
though individual alloca sizes are bounded implicitly by what
can fit into a UDP packet, as a side effect of the earlier
successful send operation).

(cherry picked from commit bc779a1a5b3035133024b21e2f339fe4219fb11c)
(cherry picked from commit bdce95930e1d9a7d013d1ba78740243491262879)

diff --git a/sunrpc/clnt_udp.c b/sunrpc/clnt_udp.c
index a6cf5f1ca73328cd568433b31c97fa94d9b12971..4d9acb1e6a6bbad9440a87b59a3e8c1fb92a7b4e 100644 (file)
--- a/sunrpc/clnt_udp.c
+++ b/sunrpc/clnt_udp.c
@@ -388,9 +388,15 @@ send_again:
          struct sock_extended_err *e;
          struct sockaddr_in err_addr;
          struct iovec iov;
-         char *cbuf = (char *) alloca (outlen + 256);
+         char *cbuf = malloc (outlen + 256);
          int ret;
 
+         if (cbuf == NULL)
+           {
+             cu->cu_error.re_errno = errno;
+             return (cu->cu_error.re_status = RPC_CANTRECV);
+           }
+
          iov.iov_base = cbuf + 256;
          iov.iov_len = outlen;
          msg.msg_name = (void *) &err_addr;
@@ -415,10 +421,12 @@ send_again:
                 cmsg = CMSG_NXTHDR (&msg, cmsg))
              if (cmsg->cmsg_level == SOL_IP && cmsg->cmsg_type == IP_RECVERR)
                {
+                 free (cbuf);
                  e = (struct sock_extended_err *) CMSG_DATA(cmsg);
                  cu->cu_error.re_errno = e->ee_errno;
                  return (cu->cu_error.re_status = RPC_CANTRECV);
                }
+         free (cbuf);
        }
 #endif
       do