kconfig: fix segv fault in menuconfig

With specific configurations requesting help for certain
menu lines caused menuconfig to crash.
This was tracked down to a null pointer bug.
Thanks to "Miles Lane" <miles.lane@gmail.com> for inital reporting
and to Gabriel C <nix.or.die@googlemail.com> for the backtrace
that helped me locating the bug.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

1 files changed, 8 insertions, 5 deletions

diff --git a/scripts/kconfig/util.c b/scripts/kconfig/util.c
index e3f28b9d59f4..e1cad924c0a4 100644
--- a/scripts/kconfig/util.c
+++ b/scripts/kconfig/util.c
@@ -84,12 +84,15 @@ void str_free(struct gstr *gs)
 /* Append to growable string */
 void str_append(struct gstr *gs, const char *s)
 {
-        size_t l = strlen(gs->s) + strlen(s) + 1;
-        if (l > gs->len) {
-                gs->s   = realloc(gs->s, l);
-                gs->len = l;
+        size_t l;
+        if (s) {
+                l = strlen(gs->s) + strlen(s) + 1;
+                if (l > gs->len) {
+                        gs->s   = realloc(gs->s, l);
+                        gs->len = l;
+                }
+                strcat(gs->s, s);
         }
-        strcat(gs->s, s);
 }
 
 /* Append printf formatted string to growable string */