[Asterisk-code-review] chan pjsip: Fix PJSIP MEDIA OFFER dialplan function read. (asterisk[master])

[Richard Mudgett]

Richard Mudgett has uploaded this change for review. ( https://gerrit.asterisk.org/5850


Change subject: chan_pjsip: Fix PJSIP_MEDIA_OFFER dialplan function read.
......................................................................

chan_pjsip: Fix PJSIP_MEDIA_OFFER dialplan function read.

The construction of the returned string assumed incorrectly that the
supplied buffer would always be initialized as an empty string.  If it is
not an empty string we could overrun the supplied buffer by the length of
the non-empty buffer string plus one.  It is also theoreticaly possible
for the supplied buffer to be overrun by a string terminator during a read
operation even if the supplied buffer is an empty string.

* Fix the assumption that the supplied buffer would already be an empty
string.  The buffer is not guaranteed to contain an empty string by all
possible callers.

* Fix string terminator buffer overrun potential.

Change-Id: If6a0806806527678c8554b1dcb34fd7808aa95c9
---
M channels/pjsip/dialplan_functions.c
1 file changed, 21 insertions(+), 14 deletions(-)



  git pull ssh://gerrit.asterisk.org:29418/asterisk refs/changes/50/5850/1

diff --git a/channels/pjsip/dialplan_functions.c b/channels/pjsip/dialplan_functions.c
index 7b3434d..e2c78cd 100644
--- a/channels/pjsip/dialplan_functions.c
+++ b/channels/pjsip/dialplan_functions.c
@@ -927,36 +927,40 @@
 static int media_offer_read_av(struct ast_sip_session *session, char *buf,
 			       size_t len, enum ast_media_type media_type)
 {
-	int i, size = 0;
+	int idx;
+	size_t accum = 0;
 
-	for (i = 0; i < ast_format_cap_count(session->req_caps); i++) {
-		struct ast_format *fmt = ast_format_cap_get_format(session->req_caps, i);
+	/* Note: buf is not terminated while the string is being built. */
+	for (idx = 0; idx < ast_format_cap_count(session->req_caps); ++idx) {
+		struct ast_format *fmt;
+		size_t size;
 
+		fmt = ast_format_cap_get_format(session->req_caps, idx);
 		if (ast_format_get_type(fmt) != media_type) {
 			ao2_ref(fmt, -1);
 			continue;
 		}
 
-		/* add one since we'll include a comma */
+		/* Add one for a comma or terminator */
 		size = strlen(ast_format_get_name(fmt)) + 1;
 		if (len < size) {
 			ao2_ref(fmt, -1);
 			break;
 		}
+
+		/* Append the format name */
+		strcpy(buf + accum, ast_format_get_name(fmt));/* Safe */
+		ao2_ref(fmt, -1);
+
+		accum += size;
 		len -= size;
 
-		/* no reason to use strncat here since we have already ensured buf has
-                   enough space, so strcat can be safely used */
-		strcat(buf, ast_format_get_name(fmt));
-		strcat(buf, ",");
-
-		ao2_ref(fmt, -1);
+		/* The last comma on the built string will be set to the terminator. */
+		buf[accum - 1] = ',';
 	}
 
-	if (size) {
-		/* remove the extra comma */
-		buf[strlen(buf) - 1] = '\0';
-	}
+	/* Remove the trailing comma or terminate an empty buffer. */
+	buf[accum ? accum - 1 : 0] = '\0';
 	return 0;
 }
 
@@ -996,6 +1000,9 @@
 		return media_offer_read_av(channel->session, buf, len, AST_MEDIA_TYPE_AUDIO);
 	} else if (!strcmp(data, "video")) {
 		return media_offer_read_av(channel->session, buf, len, AST_MEDIA_TYPE_VIDEO);
+	} else {
+		/* Ensure that the buffer is empty */
+		buf[0] = '\0';
 	}
 
 	return 0;

-- 
To view, visit https://gerrit.asterisk.org/5850
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Gerrit-Project: asterisk
Gerrit-Branch: master
Gerrit-MessageType: newchange
Gerrit-Change-Id: If6a0806806527678c8554b1dcb34fd7808aa95c9
Gerrit-Change-Number: 5850
Gerrit-PatchSet: 1
Gerrit-Owner: Richard Mudgett <rmudgett at digium.com>
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