Fix memory corruption in PMAP_CALLIT code

 - A PMAP_CALLIT call comes in on IPv4 UDP
 - rpcbind duplicates the caller's address to a netbuf and stores it in
   FINFO[0].caller_addr. caller_addr->buf now points to a memory region A
   with a size of 16 bytes
 - rpcbind forwards the call to the local service, receives a reply
 - when processing the reply, it does this in xprt_set_caller:
    xprt->xp_rtaddr = *FINFO[0].caller_addr
   It sends out the reply, and then frees the netbuf caller_addr and
   caller_addr.buf.
   However, it does not clear xp_rtaddr, so xp_rtaddr.buf now refers
   to memory region A, which is free.
 - When the next call comes in on the UDP/IPv4 socket, svc_dg_recv will
   be called, which will set xp_rtaddr to the client's address.
   It will reuse the buffer inside xp_rtaddr, ie it will write a
   sockaddr_in to region A

Some time down the road, an incoming TCP connection is accepted,
allocating a fresh SVCXPRT. The memory region A is inside the
new SVCXPRT

 - While processing the TCP call, another UDP call comes in, again
   overwriting region A with the client's address
 - TCP client closes connection. In svc_destroy, we now trip over
   the garbage left in region A

We ran into the case where a commercial scanner was triggering
occasional rpcbind segfaults. The core file that was captured showed
a corrupted xprt->xp_netid pointer that was really a sockaddr_in.

Signed-off-by: Olaf Kirch <okir@suse.de>
Signed-off-by: Steve Dickson <steved@redhat.com>

1 files changed, 22 insertions, 1 deletions

diff --git a/src/rpcb_svc_com.c b/src/rpcb_svc_com.c
index ff9ce6b..4ae93f1 100644
--- a/src/rpcb_svc_com.c
+++ b/src/rpcb_svc_com.c
@@ -1183,12 +1183,33 @@ check_rmtcalls(struct pollfd *pfds, int nfds)
 	return (ncallbacks_found);
 }
 
+/*
+ * This is really a helper function defined in libtirpc, 
+ * but unfortunately, it hasn't been exported yet.
+ */
+static struct netbuf *
+__rpc_set_netbuf(struct netbuf *nb, const void *ptr, size_t len)
+{
+	if (nb->len != len) {
+		if (nb->len)
+			mem_free(nb->buf, nb->len);
+		nb->buf = mem_alloc(len);
+		if (nb->buf == NULL)
+			return NULL;
+
+		nb->maxlen = nb->len = len;
+	}
+	memcpy(nb->buf, ptr, len);
+	return nb;
+}
+
 static void
 xprt_set_caller(SVCXPRT *xprt, struct finfo *fi)
 {
+	const struct netbuf *caller = fi->caller_addr;
 	u_int32_t *xidp;
 
-	*(svc_getrpccaller(xprt)) = *(fi->caller_addr);
+	__rpc_set_netbuf(svc_getrpccaller(xprt), caller->buf, caller->len);
 	xidp = __rpcb_get_dg_xidp(xprt);
 	*xidp = fi->caller_xid;
 }