String overscan issues in ssmtp (potential for memory corruption)

[Syed-Shahrukh-OSSRevival]

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=623856

Possible fix

--- a/ssmtp.c
+++ b/ssmtp.c
@@ -260,7 +260,7 @@ char *strip_post_ws(char *str)
 	char *p;
 
 	p = (str + strlen(str));
-	while(isspace(*--p)) {
+	while(p != str && isspace(*--p)) {
 		*p = (char)NULL;
 	}
 
@@ -299,7 +299,7 @@ char *addr_parse(char *str)
 
 	q = strip_pre_ws(p);
 	if(*q == '(') {
-		while((*q++ != ')'));
+		while(*q && *q++ != ')');
 	}
 	p = strip_pre_ws(q);
 
@@ -309,8 +309,11 @@ char *addr_parse(char *str)
 
 	q = strip_post_ws(p);
 	if(*q == ')') {
-		while((*--q != '('));
 		*q = (char)NULL;
+		while(q != p && *--q != '(');
+		if (*q == '(') {
+			*q = (char)NULL;
+		}
 	}
 	(void)strip_post_ws(p);