[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

830

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

[vitalybuka]

compiler-rt/lib/msan/msan_interceptors.cpp

830

discussed offline, keep as is

compiler-rt/lib/msan/msan_interceptors.cpp

 #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();
   int res = REAL(gethostname)(name, len);
-  if (!res) {
+  if (!res || (res == -1 && errno == errno_ENAMETOOLONG)) {
     SIZE_T real_len = REAL(strnlen)(name, len);
     if (real_len < len)
       ++real_len;
     __msan_unpoison(name, real_len);
   }
   return res;
 }
 

compiler-rt/lib/msan/tests/msan_test.cpp

TEST(MemorySanitizer, uname) {
   EXPECT_NOT_POISONED(strlen(u.sysname));
   EXPECT_NOT_POISONED(strlen(u.nodename));
   EXPECT_NOT_POISONED(strlen(u.release));
   EXPECT_NOT_POISONED(strlen(u.version));
   EXPECT_NOT_POISONED(strlen(u.machine));
 }
 
 TEST(MemorySanitizer, gethostname) {
-  char buf[100];
-  int res = gethostname(buf, 100);
-  ASSERT_EQ(0, res);
+  char buf[1000];
+  EXPECT_EQ(-1, gethostname(buf, 1));
+  EXPECT_EQ(ENAMETOOLONG, errno);
+  EXPECT_NOT_POISONED(buf[0]);
+  EXPECT_POISONED(buf[1]);
+
+  __msan_poison(buf, sizeof(buf));
+  EXPECT_EQ(0, gethostname(buf, sizeof(buf)));
   EXPECT_NOT_POISONED(strlen(buf));
 }
 
 #if !defined(__FreeBSD__) && !defined(__NetBSD__)
 TEST(MemorySanitizer, sysinfo) {
   struct sysinfo info;
   int res = sysinfo(&info);
   ASSERT_EQ(0, res);

compiler-rt/lib/sanitizer_common/sanitizer_errno_codes.h

 #ifndef SANITIZER_ERRNO_CODES_H
 #define SANITIZER_ERRNO_CODES_H
 
 namespace __sanitizer {
 
 #define errno_ENOMEM 12
 #define errno_EBUSY 16
 #define errno_EINVAL 22
+#define errno_ENAMETOOLONG 36
 
 // Those might not present or their value differ on different platforms.
 extern const int errno_EOWNERDEAD;
 
 }  // namespace __sanitizer
 
 #endif  // SANITIZER_ERRNO_CODES_H