Resolve crashes due to large stack allocations when using TCP

Asterisk had several places where messages received over various network
transports may be copied in a single stack allocation. In the case of TCP,
since multiple packets in a stream may be concatenated together, this can
lead to large allocations that overflow the stack.

This patch modifies those portions of Asterisk using TCP to either
favor heap allocations or use an upper bound to ensure that the stack will not
overflow:
 * For SIP, the allocation now has an upper limit
 * For HTTP, the allocation is now a heap allocation instead of a stack
   allocation
 * For XMPP (in res_jabber), the allocation has been eliminated since it was
   unnecesary.

Note that the HTTP portion of this issue was independently found by Brandon
Edwards of Exodus Intelligence.

(issue ASTERISK-20658)
Reported by: wdoekes, Brandon Edwards
Tested by: mmichelson, wdoekes
patches:
  ASTERISK-20658_res_jabber.c.patch uploaded by mmichelson (license 5049)
  issueA20658_http_postvars_use_malloc2.patch uploaded by wdoekes (license 5674)
  issueA20658_limit_sip_packet_size3.patch uploaded by wdoekes (license 5674)
........

Merged revisions 378269 from http://svn.asterisk.org/svn/asterisk/branches/1.8
........

Merged revisions 378286 from http://svn.asterisk.org/svn/asterisk/branches/10
........

Merged revisions 378287 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@378288 65c4cc65-6c06-0410-ace0-fbb531ad65f3

1 files changed, 16 insertions, 4 deletions

diff --git a/main/http.c b/main/http.c
index 44148edf8..fc2931290 100644
--- a/main/http.c
+++ b/main/http.c
@@ -611,6 +611,7 @@ struct ast_variable *ast_http_get_post_vars(
 	int content_length = 0;
 	struct ast_variable *v, *post_vars=NULL, *prev = NULL;
 	char *buf, *var, *val;
+	int res;
 
 	for (v = headers; v; v = v->next) {
 		if (!strcasecmp(v->name, "Content-Type")) {
@@ -623,20 +624,28 @@ struct ast_variable *ast_http_get_post_vars(
 
 	for (v = headers; v; v = v->next) {
 		if (!strcasecmp(v->name, "Content-Length")) {
-			content_length = atoi(v->value) + 1;
+			content_length = atoi(v->value);
 			break;
 		}
 	}
 
-	if (!content_length) {
+	if (content_length <= 0) {
 		return NULL;
 	}
 
-	buf = ast_alloca(content_length);
-	if (!fgets(buf, content_length, ser->f)) {
+	buf = ast_malloc(content_length + 1);
+	if (!buf) {
 		return NULL;
 	}
 
+	res = fread(buf, 1, content_length, ser->f);
+	if (res < content_length) {
+		/* Error, distinguishable by ferror() or feof(), but neither
+		 * is good. */
+		goto done;
+	}
+	buf[content_length] = '\0';
+
 	while ((val = strsep(&buf, "&"))) {
 		var = strsep(&val, "=");
 		if (val) {
@@ -654,6 +663,9 @@ struct ast_variable *ast_http_get_post_vars(
 			prev = v;
 		}
 	}
+	
+done:
+	ast_free(buf);
 	return post_vars;
 }