[DFSan] Add custom wrapper for getsockname.

[morehouse]

Summary

The wrapper clears shadow for any bytes written to addr or addrlen.

compiler-rt/lib/dfsan/dfsan_custom.cpp

__dfsw_socketpair(int domain, int type, int protocol, int sv[2],
   int ret = socketpair(domain, type, protocol, sv);
   *ret_label = 0;
   if (ret == 0) {
     dfsan_set_label(0, sv, sizeof(*sv) * 2);
   }
   return ret;
 }
 
+SANITIZER_INTERFACE_ATTRIBUTE int __dfsw_getsockname(
+    int sockfd, struct sockaddr *addr, socklen_t *addrlen,
+    dfsan_label sockfd_label, dfsan_label addr_label, dfsan_label addrlen_label,
+    dfsan_label *ret_label) {
+  socklen_t origlen = addrlen ? *addrlen : 0;
+  int ret = getsockname(sockfd, addr, addrlen);
+  if (ret != -1 && addr && addrlen) {
+    socklen_t written_bytes = origlen < *addrlen ? origlen : *addrlen;
+    dfsan_set_label(0, addrlen, sizeof(*addrlen));
+    dfsan_set_label(0, addr, written_bytes);
+  }
+  *ret_label = 0;
+  return ret;
+}
+
 // Type of the trampoline function passed to the custom version of
 // dfsan_set_write_callback.
 typedef void (*write_trampoline_t)(
     void *callback,
     int fd, const void *buf, ssize_t count,
     dfsan_label fd_label, dfsan_label buf_label, dfsan_label count_label);
 
 // Calls to dfsan_set_write_callback() set the values in this struct.

compiler-rt/lib/dfsan/done_abilist.txt

 fun:epoll_wait=custom
 fun:fgets=custom
 fun:fstat=custom
 fun:getcwd=custom
 fun:get_current_dir_name=custom
 fun:gethostname=custom
 fun:getrlimit=custom
 fun:getrusage=custom
+fun:getsockname=custom
 fun:nanosleep=custom
 fun:pread=custom
 fun:read=custom
 fun:socketpair=custom
 fun:stat=custom
 fun:time=custom
 
 # Functions that produce an output that depend on the input (propagate the

compiler-rt/test/dfsan/custom.cpp

void test_socketpair() {
 
   dfsan_set_label(i_label, fd, sizeof(fd));
   int rv = socketpair(PF_LOCAL, SOCK_STREAM, 0, fd);
   assert(rv == 0);
   ASSERT_ZERO_LABEL(rv);
   ASSERT_READ_ZERO_LABEL(fd, sizeof(fd));
 }
 
+void test_getsockname() {
+  int sockfd = socket(AF_UNIX, SOCK_DGRAM, 0);
+  assert(sockfd != -1);
+
+  struct sockaddr addr = {};
+  socklen_t addrlen = sizeof(addr);
+  dfsan_set_label(i_label, &addr, addrlen);
+  dfsan_set_label(i_label, &addrlen, sizeof(addrlen));
+
+  int ret = getsockname(sockfd, &addr, &addrlen);
+  assert(ret != -1);
+  ASSERT_ZERO_LABEL(ret);
+  ASSERT_ZERO_LABEL(addrlen);
+  assert(addrlen < sizeof(addr));
+  ASSERT_READ_ZERO_LABEL(&addr, addrlen);
+  ASSERT_READ_LABEL(((char *)&addr) + addrlen, 1, i_label);
+
+  close(sockfd);
+}
+
 void test_write() {
   int fd = open("/dev/null", O_WRONLY);
 
   char buf[] = "a string";
   int len = strlen(buf);
 
   // The result of a write always unlabeled.
   int res = write(fd, buf, len);
#endif
   test_fgets();
   test_fstat();
   test_get_current_dir_name();
   test_getcwd();
   test_gethostname();
   test_getpwuid_r();
   test_getrlimit();
   test_getrusage();
+  test_getsockname();
   test_gettimeofday();
   test_inet_pton();
   test_localtime_r();
   test_memchr();
   test_memcmp();
   test_memcpy();
   test_memset();
   test_nanosleep();