app_stack: protect against missing parameters to STACK_PEEK and LOCAL_PEEK

STACK_PEEK requires 2 parameters and LOCAL_PEEK requires 1 parameter.  This
protects against situations where those parameters are blank or missing by
logging an error and returning.

(closes issue ASTERISK-23220)
Reported by: James Sharp
........

Merged revisions 407100 from http://svn.asterisk.org/svn/asterisk/branches/1.8


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/11@407103 65c4cc65-6c06-0410-ace0-fbb531ad65f3

apps/app_stack.c

@@ -763,6 +763,12 @@ static int peek_read(struct ast_channel *chan, const char *cmd, char *data, char
 	}
 
 	AST_STANDARD_RAW_ARGS(args, data);
+
+	if (ast_strlen_zero(args.n) || ast_strlen_zero(args.name)) {
+		ast_log(LOG_ERROR, "LOCAL_PEEK requires parameters n and varname\n");
+		return -1;
+	}
+
 	n = atoi(args.n);
 	*buf = '\0';
 
@@ -802,6 +808,11 @@ static int stackpeek_read(struct ast_channel *chan, const char *cmd, char *data,
 	data = ast_strdupa(data);
 	AST_STANDARD_APP_ARGS(args, data);
 
+	if (ast_strlen_zero(args.n) || ast_strlen_zero(args.which)) {
+		ast_log(LOG_ERROR, "STACK_PEEK requires parameters n and which\n");
+		return -1;
+	}
+
 	n = atoi(args.n);
 	if (n <= 0) {
 		ast_log(LOG_ERROR, "STACK_PEEK must be called with a positive peek value\n");