[asan] Don't reset non-default user handler if allow_user_signal_handler is true.

[eugenis]

test/asan/TestCases/Linux/preinstalled_signal.cc

48

I don't like this at all. This is a mode that is not supposed to work.

Could you set a signal handler in preinit_array?
On Linux (and new-ish Android) preinit_array ctors get argc/argv/envp just as main().

[vitalybuka]

test/asan/TestCases/Linux/preinstalled_signal.cc

48

No, asan also uses preinit_array and will be executed before this.

[vitalybuka]

Load asan with LD_PRELOAD

[vitalybuka]

8 -> NSIG/8

[eugenis]

test/asan/TestCases/Linux/preinstalled_signal.cc

37

AFAIK sigset_t and kernel_sigset_t may be different in size.
Look in sanitizer_platform_limits_posix.h

42

Maybe limit the test to x86/x86_64? There are just too many things that can go wrong on different platforms.

48

is that SA_RESTORER?

[vitalybuka]

Remove sigset_t

test/asan/TestCases/Linux/preinstalled_signal.cc

37

I don't use it.

42

I'd limit if we see failures.
On a quick look into kernel code, arm should handle calls without restorer, mips and powerpc does not check this field at all.

48

Yes, but I don't see headers defining it

[vitalybuka]

Simplify return from main.

[eugenis]

LGTM

lib/sanitizer_common/sanitizer_posix_libcdep.cc

void UnsetAlternateSignalStack() {
   UnmapOrDie(oldstack.ss_sp, oldstack.ss_size);
 }
 
 static void MaybeInstallSigaction(int signum,
                                   SignalHandlerType handler) {
   if (!IsHandledDeadlySignal(signum))
     return;
   struct sigaction sigact;
+  if (common_flags()->allow_user_signal_handler) {
+    internal_memset(&sigact, 0, sizeof(sigact));
+    CHECK_EQ(0, internal_sigaction(signum, nullptr, &sigact));
+    if (sigact.sa_flags & SA_SIGINFO) {
+      if (sigact.sa_sigaction) return;
+    } else {
+      if (sigact.sa_handler != SIG_DFL && sigact.sa_handler != SIG_IGN &&
+          sigact.sa_handler != SIG_ERR) {
+        return;
+      }
+    }
+  }
+
   internal_memset(&sigact, 0, sizeof(sigact));
   sigact.sa_sigaction = (sa_sigaction_t)handler;
   // Do not block the signal from being received in that signal's handler.
   // Clients are responsible for handling this correctly.
   sigact.sa_flags = SA_SIGINFO | SA_NODEFER;
   if (common_flags()->use_sigaltstack) sigact.sa_flags |= SA_ONSTACK;
   CHECK_EQ(0, internal_sigaction(signum, &sigact, nullptr));
   VReport(1, "Installed the sigaction for signal %d\n", signum);

test/asan/TestCases/Linux/preinstalled_signal.cc

+// RUN: %clangxx -std=c++11 %s -ldl -o %t
+
+// RUN: %env_asan_opts=verify_asan_link_order=false:allow_user_signal_handler=true not %run %t %shared_libasan 0 0 2>&1 | FileCheck %s
+// RUN: %env_asan_opts=verify_asan_link_order=false:allow_user_signal_handler=true not %run %t %shared_libasan 1 1 2>&1 | FileCheck --check-prefix=CHECK-HANDLER %s
+// RUN: %env_asan_opts=verify_asan_link_order=false:allow_user_signal_handler=true not %run %t %shared_libasan 2 1 2>&1 | FileCheck --check-prefix=CHECK-ACTION %s
+
+// RUN: %env_asan_opts=verify_asan_link_order=false:allow_user_signal_handler=false not %run %t %shared_libasan 0 0 2>&1 | FileCheck %s
+// RUN: %env_asan_opts=verify_asan_link_order=false:allow_user_signal_handler=false not %run %t %shared_libasan 1 0 2>&1 | FileCheck %s
+// RUN: %env_asan_opts=verify_asan_link_order=false:allow_user_signal_handler=false not %run %t %shared_libasan 2 0 2>&1 | FileCheck %s
+
+// REQUIRES: asan-dynamic-runtime
+
+#include <assert.h>
+#include <dlfcn.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+const char *handler = NULL;
+
+void SigHandler(int signum) { handler = "TestSigHandler"; }
+
+void SigAction(int, siginfo_t *, void *) { handler = "TestSigAction"; }
+
+int main(int argc, char *argv[]) {
+  struct sigaction sigact = {};
+  sigaction(SIGSEGV, NULL, &sigact);
+  assert(sigact.sa_handler == SIG_DFL || sigact.sa_handler == SIG_IGN);
+
+  const char *asan_rt = argv[1];
+  int handler_type = atoi(argv[2]);
+  bool keep_user_handler = atoi(argv[3]);
+
+  switch (handler_type) {
+  case 1:
+    sigact = {};
+    sigact.sa_handler = &SigHandler;
+    sigaction(SIGSEGV, &sigact, NULL);
+    break;
+  case 2:
+    sigact = {};
+    sigact.sa_flags = SA_SIGINFO | SA_NODEFER;
+    sigact.sa_sigaction = &SigAction;
+    sigaction(SIGSEGV, &sigact, NULL);
+    break;
+  };
+
+  void *asan = dlopen(asan_rt, RTLD_NOW);
+  assert(asan);
+
+  struct sigaction sigact_asan = {};
+  sigaction(SIGSEGV, NULL, &sigact_asan);
+
+  assert(sigact_asan.sa_handler != SIG_DFL);
+  assert(sigact_asan.sa_handler != SIG_IGN);
+
+  assert(keep_user_handler == (sigact_asan.sa_handler == sigact.sa_handler));
+  assert(keep_user_handler ==
+         (sigact_asan.sa_sigaction == sigact.sa_sigaction));
+
+  raise(SIGSEGV);
+
+  printf("%s\n", handler);
+
+  dlclose(asan);
+  return !!handler;
+}
+
+// CHECK-NOT: TestSig
+// CHECK: ASAN:DEADLYSIGNAL
+
+// CHECK-HANDLER-NOT: ASAN:DEADLYSIGNAL
+// CHECK-HANDLER: TestSigHandler
+
+// CHECK-ACTION-NOT: ASAN:DEADLYSIGNAL
+// CHECK-ACTION: TestSigAction