rpcbind: pair all svc_getargs() calls with svc_freeargs() to avoid memory leak

This patch is to address CVE-2017-8779 "rpcbomb" in rpcbind, discussed at [1], [2], [3]. The last link suggests this issue is actually a bug in rpcbind, which led me here.

The leak caused by the reproducer at [4] appears to come from rpcb_service_4(), in the case where svc_getargs() returns false and the function had an early return, rather than passing through the cleanup path at done:, as would otherwise occur.

It also addresses a couple of other locations where the same fault seems to exist, though I haven't been able to exercise those. I hope someone more intimate with rpc(3) can confirm my understanding is correct, and that I haven't introduced any new bugs.

Without this patch, using the reproducer (and variants) repeatedly against rpcbind with a numBytes argument of 1_000_000_000, /proc/$(pidof rpcbind)/status reports VmSize increase of 976564 kB each call, and VmRSS increase of around 260 kB every 33 calls - the specific numbers are probably an artifact of my rhel/glibc version. With the patch, there is a small (~50 kB) VmSize increase with the first message, but thereafter both VmSize and VmRSS remain steady.

[1]: http://seclists.org/oss-sec/2017/q2/209
[2]: https://bugzilla.redhat.com/show_bug.cgi?id=1448124
[3]: https://sourceware.org/ml/libc-alpha/2017-05/msg00129.html
[4]: https://github.com/guidovranken/rpcbomb/

Signed-off-by Doran Moppert <[email protected]>

---
 src/pmap_svc.c     | 56 +++++++++++++++++++++++++++++++++++++++++++++---------
 src/rpcb_svc.c     |  2 +-
 src/rpcb_svc_4.c   |  2 +-
 src/rpcb_svc_com.c |  8 ++++++++
 4 files changed, 57 insertions(+), 11 deletions(-)

src/pmap_svc.c +47 -9

index 4c744fe..e926cdc 100644
@@ -175,6 +175,7 @@ pmapproc_change(struct svc_req *rqstp /*__unused*/, SVCXPRT *xprt, unsigned long
 	long ans;
 	uid_t uid;
 	char uidbuf[32];
+	int rc = TRUE;
 
 	/*
 	 * Can't use getpwnam here. We might end up calling ourselves

@@ -194,7 +195,8 @@ pmapproc_change(struct svc_req *rqstp /*__unused*/, SVCXPRT *xprt, unsigned long
 
 	if (!svc_getargs(xprt, (xdrproc_t) xdr_pmap, (char *)&reg)) {
 		svcerr_decode(xprt);
-		return (FALSE);
+		rc = FALSE;
+		goto done;
 	}
 #ifdef RPCBIND_DEBUG
 	if (debugging)

@@ -205,7 +207,8 @@ pmapproc_change(struct svc_req *rqstp /*__unused*/, SVCXPRT *xprt, unsigned long
 
 	if (!check_access(xprt, op, reg.pm_prog, PMAPVERS)) {
 		svcerr_weakauth(xprt);
-		return (FALSE);
+		rc = (FALSE);
+		goto done;
 	}
 
 	rpcbreg.r_prog = reg.pm_prog;

@@ -258,7 +261,16 @@ done_change:
 		rpcbs_set(RPCBVERS_2_STAT, ans);
 	else
 		rpcbs_unset(RPCBVERS_2_STAT, ans);
-	return (TRUE);
+done:
+	if (!svc_freeargs(xprt, (xdrproc_t) xdr_pmap, (char *)&reg)) {
+		if (debugging) {
+			(void) xlog(LOG_DEBUG, "unable to free arguments\n");
+			if (doabort) {
+				rpcbind_abort();
+			}
+		}
+	}
+	return (rc);
 }
 
 /* ARGSUSED */

@@ -272,15 +284,18 @@ pmapproc_getport(struct svc_req *rqstp /*__unused*/, SVCXPRT *xprt)
 #ifdef RPCBIND_DEBUG
 	char *uaddr;
 #endif
+	int rc = TRUE;
 
 	if (!svc_getargs(xprt, (xdrproc_t) xdr_pmap, (char *)&reg)) {
 		svcerr_decode(xprt);
-		return (FALSE);
+		rc = FALSE;
+		goto done;
 	}
 
 	if (!check_access(xprt, PMAPPROC_GETPORT, reg.pm_prog, PMAPVERS)) {
 		svcerr_weakauth(xprt);
-		return FALSE;
+		rc = FALSE;
+		goto done;
 	}
 
 #ifdef RPCBIND_DEBUG

@@ -330,21 +345,34 @@ pmapproc_getport(struct svc_req *rqstp /*__unused*/, SVCXPRT *xprt)
 		pmap_ipprot2netid(reg.pm_prot) ?: "<unknown>",
 		port ? udptrans : "");
 
-	return (TRUE);
+done:
+	if (!svc_freeargs(xprt, (xdrproc_t) xdr_pmap, (char *)&reg)) {
+		if (debugging) {
+			(void) xlog(LOG_DEBUG, "unable to free arguments\n");
+			if (doabort) {
+				rpcbind_abort();
+			}
+		}
+	}
+	return (rc);
 }
 
 /* ARGSUSED */
 static bool_t
 pmapproc_dump(struct svc_req *rqstp /*__unused*/, SVCXPRT *xprt)
 {
+	int rc = TRUE;
+
 	if (!svc_getargs(xprt, (xdrproc_t)xdr_void, NULL)) {
 		svcerr_decode(xprt);
-		return (FALSE);
+		rc = FALSE;
+		goto done;
 	}
 
 	if (!check_access(xprt, PMAPPROC_DUMP, 0, PMAPVERS)) {
 		svcerr_weakauth(xprt);
-		return FALSE;
+		rc = FALSE;
+		goto done;
 	}
 
 	if ((!svc_sendreply(xprt, (xdrproc_t) xdr_pmaplist_ptr,

@@ -354,7 +382,17 @@ pmapproc_dump(struct svc_req *rqstp /*__unused*/, SVCXPRT *xprt)
 			rpcbind_abort();
 		}
 	}
-	return (TRUE);
+
+done:
+	if (!svc_freeargs(xprt, (xdrproc_t) xdr_pmap, (char *)NULL)) {
+		if (debugging) {
+			(void) xlog(LOG_DEBUG, "unable to free arguments\n");
+			if (doabort) {
+				rpcbind_abort();
+			}
+		}
+	}
+	return (rc);
 }
 
 int pmap_netid2ipprot(const char *netid)

src/rpcb_svc.c +1 -1

index 709e3fb..091f530 100644
@@ -166,7 +166,7 @@ rpcb_service_3(struct svc_req *rqstp, SVCXPRT *transp)
 		svcerr_decode(transp);
 		if (debugging)
 			(void) xlog(LOG_DEBUG, "rpcbind: could not decode");
-		return;
+		goto done;
 	}
 
 	if (rqstp->rq_proc == RPCBPROC_SET

src/rpcb_svc_4.c +1 -1

index 5094879..eebbbbe 100644
@@ -218,7 +218,7 @@ rpcb_service_4(struct svc_req *rqstp, SVCXPRT *transp)
 		svcerr_decode(transp);
 		if (debugging)
 			(void) xlog(LOG_DEBUG, "rpcbind: could not decode\n");
-		return;
+		goto done;
 	}
 
 	if (rqstp->rq_proc == RPCBPROC_SET

src/rpcb_svc_com.c +8 -0

index 5862c26..cb63afd 100644
@@ -927,6 +927,14 @@ error:
 	if (call_msg.rm_xid != 0)
 		(void) free_slot_by_xid(call_msg.rm_xid);
 out:
+	if (!svc_freeargs(transp, (xdrproc_t) xdr_rmtcall_args, (char *) &a)) {
+		if (debugging) {
+			(void) xlog(LOG_DEBUG, "unable to free arguments\n");
+			if (doabort) {
+				rpcbind_abort();
+			}
+		}
+	}
 	if (local_uaddr)
 		free(local_uaddr);
 	if (buf_alloc)