srtp: fix bad memory access

* fix non-initialized memory at SRTP session creation.
* fix invalid access when SRTP session is free in some conditions.

Change-Id: I95a1e2cd45b8007cb20445ca219f8e667e977656
Reviewed-by: Anthony Léonard <anthony.leonard@savoirfairelinux.com>

src/media/socket_pair.cpp

@@ -25,6 +25,7 @@
 #include "ice_socket.h"
 #include "libav_utils.h"
 #include "logger.h"
+#include "security/memory.h"
 
 #include <iostream>
 #include <string>
@@ -69,6 +70,8 @@ class SRTPProtoContext {
 public:
     SRTPProtoContext(const char* out_suite, const char* out_key,
                      const char* in_suite, const char* in_key) {
+        ring_secure_memzero(&srtp_out, sizeof(srtp_out));
+        ring_secure_memzero(&srtp_in, sizeof(srtp_in));
         if (out_suite && out_key) {
             // XXX: see srtp_open from libavformat/srtpproto.c
             if (ff_srtp_set_crypto(&srtp_out, out_suite, out_key) < 0) {

src/media/srtp.c

@@ -42,10 +42,14 @@ void ff_srtp_free(struct SRTPContext *s)
         return;
     // aes and hmac have an opaque pointer type.
     // No API to safely erase them, so just re-init with "dummy keys" to sanitize them
+    if (s->aes) {
         av_aes_init(s->aes, zero_buffer, 128, 0);
-    av_hmac_init(s->hmac, zero_buffer, sizeof(s->rtp_auth));
         av_freep(&s->aes);
+    }
+    if (s->hmac) {
+        av_hmac_init(s->hmac, zero_buffer, sizeof(s->rtp_auth));
         av_hmac_free(s->hmac);
+    }
     ring_secure_memzero(s, sizeof(*s));
 }