[Msan] Fix the if_indextoname.cc test to pass on FreeBSD

[kutuzov.viktor.84]

Summary

On FreeBSD if_indextoname() leverages strncpy() that unpoisons the whole name buffer, what in turn results in the assertion following the if_indextoname() call to fail:

if (!if_indextoname(1, ifname)) {
  ...
}
assert(strlen(ifname) + 1 == __msan_test_shadow(ifname, sizeof(ifname)));

[eugenis]

I don't like it. strncpy zero-initializes this memory whether it's called from inside another interceptor or not.

I'd just change the assert to show that the first strlen()+1 bytes are unpoisoned, without testing the rest of the buffer.

Maybe change the if_indextoname interceptor to poison this area?

[kutuzov.viktor.84]

Maybe change the if_indextoname interceptor to poison this area?

I would expect all functions handling buffers of specified sizes behave consistently in this regard. I mean, given strncpy() unpoisons its destination buffer all over its size, then probably if_indextoname() should do the same.

[kutuzov.viktor.84]

Updated.

[eugenis]

LGTM

compiler-rt/trunk/lib/sanitizer_common/sanitizer_platform_interceptors.h

 #define SANITIZER_INTERCEPT_TLS_GET_ADDR \
   SI_FREEBSD || SI_LINUX_NOT_ANDROID
 
 #define SANITIZER_INTERCEPT_LISTXATTR SI_LINUX
 #define SANITIZER_INTERCEPT_GETXATTR SI_LINUX
 #define SANITIZER_INTERCEPT_GETRESID SI_LINUX
 #define SANITIZER_INTERCEPT_GETIFADDRS \
   SI_FREEBSD || SI_LINUX_NOT_ANDROID || SI_MAC
-#define SANITIZER_INTERCEPT_IF_INDEXTONAME SI_LINUX_NOT_ANDROID || SI_MAC
+#define SANITIZER_INTERCEPT_IF_INDEXTONAME \
+  SI_FREEBSD || SI_LINUX_NOT_ANDROID || SI_MAC
 #define SANITIZER_INTERCEPT_CAPGET SI_LINUX_NOT_ANDROID
 #define SANITIZER_INTERCEPT_AEABI_MEM SI_LINUX && defined(__arm__)
 #define SANITIZER_INTERCEPT___BZERO SI_MAC
 #define SANITIZER_INTERCEPT_FTIME !SI_FREEBSD && SI_NOT_WINDOWS
 #define SANITIZER_INTERCEPT_XDR SI_LINUX_NOT_ANDROID
 #define SANITIZER_INTERCEPT_TSEARCH SI_LINUX_NOT_ANDROID || SI_MAC
 #define SANITIZER_INTERCEPT_LIBIO_INTERNALS SI_LINUX_NOT_ANDROID
 #define SANITIZER_INTERCEPT_FOPEN SI_NOT_WINDOWS

compiler-rt/trunk/test/msan/if_indextoname.cc

 int main(int argc, char *argv[]) {
   char ifname[IF_NAMESIZE + 1];
   assert(0 == __msan_test_shadow(ifname, sizeof(ifname)));
   if (!if_indextoname(1, ifname)) {
     assert(errno == ENXIO);
     printf("No network interfaces found.\n");
     return 0;
   }
-  assert(strlen(ifname) + 1 == __msan_test_shadow(ifname, sizeof(ifname)));
+  assert(strlen(ifname) + 1 <= __msan_test_shadow(ifname, sizeof(ifname)));
   return 0;
 }