when parsing a text configuration option, ensure that the buffer on the stack is actually large enough to hold the legal values of that option, and also ensure that sscanf() knows to stop parsing if it would overrun the buffer (without these changes, specifying "buffers=...,immediate" would overflow the buffer on the stack, and could not have worked as expected)

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@147681 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_dahdi.c

@@ -10990,8 +10990,9 @@ static int process_dahdi(struct dahdi_chan_conf *confp, const char *cat, struct
 					return -1;
 		} else if (!strcasecmp(v->name, "buffers")) {
 			int res;
-			char policy[8] = "";
-			res = sscanf(v->value, "%d,%s", &confp->chan.buf_no, policy);
+			char policy[21] = "";
+
+			res = sscanf(v->value, "%d,%20s", &confp->chan.buf_no, policy);
 			if (res != 2) {
 				ast_log(LOG_WARNING, "Parsing buffers option data failed, using defaults.\n");
 				confp->chan.buf_no = numbufs;