sanitizer: fix crash with textdomain(NULL) interceptor

[Lekensteyn]

Summary

The textdomain function accepts a NULL parameter (and should then return the
current message domain). Add a check for this and include ASAN tests.

Link: https://github.com/google/sanitizers/issues/787

[kcc]

LGTM, thanks!
Do you have commit access?

[Lekensteyn]

In D32318#732863, @kcc wrote:

LGTM, thanks!
Do you have commit access?

Not yet (requested it earliet today), so please merge it for me (or we could just wait for Chris). Thanks!

lib/sanitizer_common/sanitizer_common_interceptors.inc

 #else
 #define INIT_STRNLEN
 #endif
 
 #if SANITIZER_INTERCEPT_TEXTDOMAIN
 INTERCEPTOR(char*, textdomain, const char *domainname) {
   void *ctx;
   COMMON_INTERCEPTOR_ENTER(ctx, textdomain, domainname);
-  COMMON_INTERCEPTOR_READ_STRING(ctx, domainname, 0);
+  if (domainname) COMMON_INTERCEPTOR_READ_STRING(ctx, domainname, 0);
   char *domain = REAL(textdomain)(domainname);
   if (domain) {
     COMMON_INTERCEPTOR_INITIALIZE_RANGE(domain, REAL(strlen)(domain) + 1);
   }
   return domain;
 }
 #define INIT_TEXTDOMAIN COMMON_INTERCEPT_FUNCTION(textdomain)
 #else

test/asan/TestCases/textdomain.c

+// RUN: %clang_asan -O0 -g %s -o %t
+// RUN: %env_asan_opts=strict_string_checks=1 %run %t
+
+#include <stdlib.h>
+#include <libintl.h>
+
+int main() {
+  textdomain(NULL);
+  return 0;
+}