[msan] Skip memcpy interceptor called by gethostname

[vitalybuka]

Summary

No test as reproducer requires particular glibc build.

[eugenis]

I'm concerned that this may break more things that it will fix.
We may have code relying on initialization done by an memcpy call from under some other interceptor. That's not very reliable, of course, and ideally all such effects should be handled in the top-level interceptor, so this change looks like movement in the right direction.
But please test it thoroughly.

Could you explain in more detail what is going wrong without it? It looks like gethostname interceptor updates shadow for all its side effects correctly.

[vitalybuka]

corrected fix

[vitalybuka]

undo unrelated changes

[vitalybuka]

undo unrelated changes for real

[eugenis]

LGTM

compiler-rt/lib/msan/msan_interceptors.cpp

833

(res >= 0 || errno == errno_ENAMETOOLONG)

[vitalybuka]

compiler-rt/lib/msan/msan_interceptors.cpp

833

discussed offline, keep as is

compiler-rt/lib/msan/msan_interceptors.cpp

 }
 #define MSAN_MAYBE_INTERCEPT_FREAD_UNLOCKED INTERCEPT_FUNCTION(fread_unlocked)
 #else
 #define MSAN_MAYBE_INTERCEPT_FREAD_UNLOCKED
 #endif
 
 #if !SANITIZER_NETBSD
 INTERCEPTOR(void *, mempcpy, void *dest, const void *src, SIZE_T n) {
+  if (IsInInterceptorScope())
+    return REAL(memcpy)(dest, src, n);
   return (char *)__msan_memcpy(dest, src, n) + n;
 }
 #define MSAN_MAYBE_INTERCEPT_MEMPCPY INTERCEPT_FUNCTION(mempcpy)
 #else
 #define MSAN_MAYBE_INTERCEPT_MEMPCPY
 #endif
 
 INTERCEPTOR(void *, memccpy, void *dest, const void *src, int c, SIZE_T n) {

 #define MSAN_MAYBE_INTERCEPT___GETRLIMIT
 #define MSAN_MAYBE_INTERCEPT_GETRLIMIT64
 #define MSAN_MAYBE_INTERCEPT_PRLIMIT
 #define MSAN_MAYBE_INTERCEPT_PRLIMIT64
 #endif
 
 INTERCEPTOR(int, gethostname, char *name, SIZE_T len) {
   ENSURE_MSAN_INITED();
+  InterceptorScope interceptor_scope;
   int res = REAL(gethostname)(name, len);
   if (!res) {
     SIZE_T real_len = REAL(strnlen)(name, len);
     if (real_len < len)
       ++real_len;
     __msan_unpoison(name, real_len);
   }
   return res;
 }
 

 #define COMMON_INTERCEPTOR_MEMMOVE_IMPL(ctx, to, from, size) \
   {                                                          \
     (void)ctx;                                               \
     return __msan_memmove(to, from, size);                   \
   }
 #define COMMON_INTERCEPTOR_MEMCPY_IMPL(ctx, to, from, size) \
   {                                                         \
     (void)ctx;                                              \
+    if (IsInInterceptorScope())                             \
+      return REAL(memcpy)(to, from, size);                  \
     return __msan_memcpy(to, from, size);                   \
   }
 
 #define COMMON_INTERCEPTOR_COPY_STRING(ctx, to, from, size) \
   do {                                                      \
     GET_STORE_STACK_TRACE;                                  \
     CopyShadowAndOrigin(to, from, size, &stack);            \
     __msan_unpoison(to + size, 1);                          \