sasl: Rework memory handling in spice_channel_perform_auth_sasl()

While looking at the SASL code, I noticed some memory leaks in error paths.
This commit adds a cleanup: block to free some of the memory dynamically
allocated in that function, and remove the corresponding g_free() from
the regular code flow. This should ensure that both the regular path
and the error paths free the same memory.

This fixes at least this 'mechlist' leak which I got during regular SASL
PLAIN authentication:
==3452== 6 bytes in 1 blocks are definitely lost in loss record 140 of 11,706
==3452==    at 0x4A0645D: malloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.s
==3452==    by 0x35BAC4EE6E: g_malloc (gmem.c:104)
==3452==    by 0x5BF7CAA: spice_channel_perform_auth_sasl (spice-channel.c:1440)
==3452==    by 0x5BF9033: spice_channel_recv_link_msg (spice-channel.c:1727)
==3452==    by 0x5BFAECD: spice_channel_coroutine (spice-channel.c:2348)
==3452==    by 0x5C35D6D: coroutine_trampoline (coroutine_ucontext.c:63)
==3452==    by 0x5C35A1B: continuation_trampoline (continuation.c:51)
==3452==    by 0x31342479BF: ??? (in /usr/lib64/libc-2.18.so)
==3452==    by 0x75F2940591224CFF: ???
==3452==    by 0xE756E5F: ???
==3452==    by 0xE7589BF: ???
==3452==    by 0xFFEFFF78F: ???
==3452==    by 0x5BFCD92: g_io_wait_helper (gio-coroutine.c:43)
=

1 files changed, 11 insertions, 10 deletions

diff --git a/gtk/spice-channel.c b/gtk/spice-channel.c
index ace8b94..83c7006 100644
--- a/gtk/spice-channel.c
+++ b/gtk/spice-channel.c
@@ -1348,7 +1348,7 @@ static gboolean spice_channel_perform_auth_sasl(SpiceChannel *channel)
     };
     sasl_interact_t *interact = NULL;
     guint32 len;
-    char *mechlist;
+    char *mechlist = NULL;
     const char *mechname;
     gboolean ret = FALSE;
     GSocketAddress *addr = NULL;
@@ -1403,8 +1403,6 @@ static gboolean spice_channel_perform_auth_sasl(SpiceChannel *channel)
                           saslcb,
                           SASL_SUCCESS_DATA,
                           &saslconn);
-    g_free(localAddr);
-    g_free(remoteAddr);
 
     if (err != SASL_OK) {
         g_critical("Failed to create SASL client context: %d (%s)",
@@ -1453,8 +1451,6 @@ static gboolean spice_channel_perform_auth_sasl(SpiceChannel *channel)
     spice_channel_read(channel, mechlist, len);
     mechlist[len] = '\0';
     if (c->has_error) {
-        g_free(mechlist);
-        mechlist = NULL;
         goto error;
     }
 
@@ -1470,8 +1466,6 @@ restart:
     if (err != SASL_OK && err != SASL_CONTINUE && err != SASL_INTERACT) {
         g_critical("Failed to start SASL negotiation: %d (%s)",
                    err, sasl_errdetail(saslconn));
-        g_free(mechlist);
-        mechlist = NULL;
         goto error;
     }
 
@@ -1657,15 +1651,22 @@ complete:
      * is defined to be sent unencrypted, and setting saslconn turns
      * on the SSF layer encryption processing */
     c->sasl_conn = saslconn;
-    return ret;
+    goto cleanup;
 
 error:
-    g_clear_object(&addr);
     if (saslconn)
         sasl_dispose(&saslconn);
     emit_main_context(channel, SPICE_CHANNEL_EVENT, SPICE_CHANNEL_ERROR_AUTH);
     c->has_error = TRUE; /* force disconnect */
-    return FALSE;
+    ret = FALSE;
+
+cleanup:
+    g_free(localAddr);
+    g_free(remoteAddr);
+    g_free(mechlist);
+    g_free(serverin);
+    g_clear_object(&addr);
+    return ret;
 }
 #endif /* HAVE_SASL */