[DFSan] Add custom wrapper for epoll_wait.

[morehouse]

Summary

The wrapper clears shadow for any events written.

[stephan.yichao.zhao]

compiler-rt/test/dfsan/custom.cpp

660

assert ret's label is always 0?

[morehouse]

• Check ret's label in test.

compiler-rt/lib/dfsan/dfsan_custom.cpp

 //===-- dfsan.cpp ---------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // This file is a part of DataFlowSanitizer.
 //
 // This file defines the custom functions listed in done_abilist.txt.
 //===----------------------------------------------------------------------===//
 
-#include "sanitizer_common/sanitizer_common.h"
-#include "sanitizer_common/sanitizer_internal_defs.h"
-#include "sanitizer_common/sanitizer_linux.h"
-
-#include "dfsan/dfsan.h"
-
 #include <arpa/inet.h>
 #include <assert.h>
 #include <ctype.h>
 #include <dlfcn.h>
 #include <link.h>
 #include <poll.h>
 #include <pthread.h>
 #include <pwd.h>
 #include <sched.h>
 #include <signal.h>
 #include <stdarg.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <sys/epoll.h>
 #include <sys/resource.h>
 #include <sys/select.h>
 #include <sys/stat.h>
 #include <sys/time.h>
 #include <sys/types.h>
 #include <time.h>
 #include <unistd.h>
 
+#include "dfsan/dfsan.h"
+#include "sanitizer_common/sanitizer_common.h"
+#include "sanitizer_common/sanitizer_internal_defs.h"
+#include "sanitizer_common/sanitizer_linux.h"
+
 using namespace __dfsan;
 
 #define CALL_WEAK_INTERCEPTOR_HOOK(f, ...)                                     \
   do {                                                                         \
     if (f)                                                                     \
       f(__VA_ARGS__);                                                          \
   } while (false)
 #define DECLARE_WEAK_INTERCEPTOR_HOOK(f, ...) \
if (ret == 0) {
     dfsan_set_label(0, buf, strlen(buf) + 1);
   }
   *ret_label = 0;
   dfsan_set_label(0, result, sizeof(struct passwd*));
   return ret;
 }
 
 SANITIZER_INTERFACE_ATTRIBUTE
+int __dfsw_epoll_wait(int epfd, struct epoll_event *events, int maxevents,
+                      int timeout, dfsan_label epfd_label,
+                      dfsan_label events_label, dfsan_label maxevents_label,
+                      dfsan_label timeout_label, dfsan_label *ret_label) {
+  int ret = epoll_wait(epfd, events, maxevents, timeout);
+  if (ret > 0)
+    dfsan_set_label(0, events, ret * sizeof(*events));
+  *ret_label = 0;
+  return ret;
+}
+
+SANITIZER_INTERFACE_ATTRIBUTE
 int __dfsw_poll(struct pollfd *fds, nfds_t nfds, int timeout,
                 dfsan_label dfs_label, dfsan_label nfds_label,
                 dfsan_label timeout_label, dfsan_label *ret_label) {
   int ret = poll(fds, nfds, timeout);
   if (ret >= 0) {
     for (; nfds > 0; --nfds) {
       dfsan_set_label(0, &fds[nfds - 1].revents, sizeof(fds[nfds - 1].revents));
     }

compiler-rt/lib/dfsan/done_abilist.txt

 fun:unlink=discard
 fun:uselocale=discard
 
 # Functions that produce output does not depend on the input (need to zero the
 # shadow manually).
 fun:calloc=custom
 fun:clock_gettime=custom
 fun:dlopen=custom
+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:nanosleep=custom

compiler-rt/test/dfsan/custom.cpp

 #include <pwd.h>
 #include <sched.h>
 #include <signal.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <strings.h>
+#include <sys/epoll.h>
 #include <sys/resource.h>
 #include <sys/select.h>
 #include <sys/stat.h>
 #include <sys/time.h>
 #include <sys/types.h>
 #include <time.h>
 #include <unistd.h>
 
void test_getpwuid_r() {
   dfsan_set_label(i_label, &pwd, 4);
   int ret = getpwuid_r(0, &pwd, buf, sizeof(buf), &result);
   assert(ret == 0);
   assert(strcmp(pwd.pw_name, "root") == 0);
   assert(result == &pwd);
   ASSERT_READ_ZERO_LABEL(&pwd, 4);
 }
 
+void test_epoll_wait() {
+  // Set up a pipe to monitor with epoll.
+  int pipe_fds[2];
+  int ret = pipe(pipe_fds);
+  assert(ret != -1);
+
+  // Configure epoll to monitor the pipe.
+  int epfd = epoll_create1(0);
+  assert(epfd != -1);
+  struct epoll_event event;
+  event.events = EPOLLIN;
+  event.data.fd = pipe_fds[0];
+  ret = epoll_ctl(epfd, EPOLL_CTL_ADD, pipe_fds[0], &event);
+  assert(ret != -1);
+
+  // Test epoll_wait when no events have occurred.
+  event = {};
+  dfsan_set_label(i_label, &event, sizeof(event));
+  ret = epoll_wait(epfd, &event, /*maxevents=*/1, /*timeout=*/0);
+  assert(ret == 0);
+  assert(event.events == 0);
+  assert(event.data.fd == 0);
+  ASSERT_ZERO_LABEL(ret);
+  ASSERT_READ_LABEL(&event, sizeof(event), i_label);
+
+  // Test epoll_wait when an event occurs.
+  write(pipe_fds[1], "x", 1);
+  ret = epoll_wait(epfd, &event, /*maxevents=*/1, /*timeout=*/0);
+  assert(ret == 1);
+  assert(event.events == EPOLLIN);
+  assert(event.data.fd == pipe_fds[0]);
+  ASSERT_ZERO_LABEL(ret);
+  ASSERT_READ_ZERO_LABEL(&event, sizeof(event));
+
+  // Clean up.
+  close(epfd);
+  close(pipe_fds[0]);
+  close(pipe_fds[1]);
+}
+
 void test_poll() {
   struct pollfd fd;
   fd.fd = 0;
   fd.events = POLLIN;
   dfsan_set_label(i_label, &fd.revents, sizeof(fd.revents));
   int ret = poll(&fd, 1, 1);
   ASSERT_ZERO_LABEL(fd.revents);
   assert(ret >= 0);
#endif
 
   test_bcmp();
   test_calloc();
   test_clock_gettime();
   test_ctime_r();
   test_dfsan_set_write_callback();
   test_dl_iterate_phdr();
   test_dlopen();
+  test_epoll_wait();
   test_fgets();
   test_fstat();
   test_get_current_dir_name();
   test_getcwd();
   test_gethostname();
   test_getpwuid_r();
   test_getrlimit();
   test_getrusage();