[sanitizer_common] AND signals in BlockSignals instead of deleting

compiler-rt/lib/sanitizer_common/sanitizer_linux.cpp

@@ -164,33 +164,45 @@ void SetSigProcMask(__sanitizer_sigset_t *set, __sanitizer_sigset_t *oldset) {
   CHECK_EQ(0, internal_sigprocmask(SIG_SETMASK, set, oldset));
 }
 
+// Deletes the specified signal from newset, if it is not present in oldset
+// Equivalently: newset[signum] = newset[signum] & oldset[signum]
+static void KeepUnblocked(__sanitizer_sigset_t &newset,
+                          __sanitizer_sigset_t &oldset, int signum) {
+  if (!internal_sigismember(&oldset, signum))
+    internal_sigdelset(&newset, signum);
+}
+
 // Block asynchronous signals
 void BlockSignals(__sanitizer_sigset_t *oldset) {
-  __sanitizer_sigset_t set;
-  internal_sigfillset(&set);
+  __sanitizer_sigset_t currentset;
+  SetSigProcMask(NULL, &currentset);
+
+  __sanitizer_sigset_t newset;
+  internal_sigfillset(&newset);
 #  if SANITIZER_LINUX && !SANITIZER_ANDROID
   // Glibc uses SIGSETXID signal during setuid call. If this signal is blocked
   // on any thread, setuid call hangs.
   // See test/sanitizer_common/TestCases/Linux/setuid.c.
-  internal_sigdelset(&set, 33);
+  KeepUnblocked(newset, currentset, 33);
 #  endif
 #  if SANITIZER_LINUX
   // Seccomp-BPF-sandboxed processes rely on SIGSYS to handle trapped syscalls.
   // If this signal is blocked, such calls cannot be handled and the process may
   // hang.
-  internal_sigdelset(&set, 31);
+  KeepUnblocked(newset, currentset, 31);
 
   // Don't block synchronous signals
-  internal_sigdelset(&set, SIGSEGV);
-  internal_sigdelset(&set, SIGBUS);
-  internal_sigdelset(&set, SIGILL);
-  internal_sigdelset(&set, SIGTRAP);
-  internal_sigdelset(&set, SIGABRT);
-  internal_sigdelset(&set, SIGFPE);
-  internal_sigdelset(&set, SIGPIPE);
+  // but also don't unblock signals that the user had deliberately blocked.
+  KeepUnblocked(newset, currentset, SIGSEGV);
+  KeepUnblocked(newset, currentset, SIGBUS);
+  KeepUnblocked(newset, currentset, SIGILL);
+  KeepUnblocked(newset, currentset, SIGTRAP);
+  KeepUnblocked(newset, currentset, SIGABRT);
+  KeepUnblocked(newset, currentset, SIGFPE);
+  KeepUnblocked(newset, currentset, SIGPIPE);
 #  endif
 
-  SetSigProcMask(&set, oldset);
+  SetSigProcMask(&newset, oldset);
 }
 
 ScopedBlockSignals::ScopedBlockSignals(__sanitizer_sigset_t *copy) {

compiler-rt/lib/sanitizer_common/tests/CMakeLists.txt

@@ -15,6 +15,7 @@ set(SANITIZER_UNITTESTS
   sanitizer_array_ref_test.cpp
   sanitizer_atomic_test.cpp
   sanitizer_bitvector_test.cpp
+  sanitizer_block_signals.cpp
   sanitizer_bvgraph_test.cpp
   sanitizer_chained_origin_depot_test.cpp
   sanitizer_common_test.cpp

compiler-rt/lib/sanitizer_common/tests/sanitizer_block_signals.cpp

@@ -0,0 +1,81 @@
+//===-- sanitizer_block_signals.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 sanitizer_common unit tests.
+//
+//===----------------------------------------------------------------------===//
+#include <signal.h>
+#include <stdio.h>
+
+#include "gtest/gtest.h"
+#include "sanitizer_common/sanitizer_linux.h"
+
+namespace __sanitizer {
+
+#if SANITIZER_LINUX
+volatile int received_sig = -1;
+
+void signal_handler(int signum) { received_sig = signum; }
+
+TEST(SanitizerCommon, BlockSignals) {
+  // No signals blocked
+  {
+    signal(SIGUSR1, signal_handler);
+    raise(SIGUSR1);
+    while (received_sig == -1) sleep(1);
+    EXPECT_EQ(received_sig, SIGUSR1);
+
+    received_sig = -1;
+    signal(SIGPIPE, signal_handler);
+    raise(SIGPIPE);
+    while (received_sig == -1) sleep(1);
+    EXPECT_EQ(received_sig, SIGPIPE);
+  }
+
+  // ScopedBlockSignals; SIGUSR1 should be blocked but not SIGPIPE
+  {
+    __sanitizer_sigset_t sigset = {};
+    ScopedBlockSignals block(&sigset);
+
+    received_sig = -1;
+    signal(SIGUSR1, signal_handler);
+    raise(SIGUSR1);
+    sleep(1);
+    EXPECT_EQ(received_sig, -1);
+
+    received_sig = -1;
+    signal(SIGPIPE, signal_handler);
+    raise(SIGPIPE);
+    while (received_sig == -1) sleep(1);
+    EXPECT_EQ(received_sig, SIGPIPE);
+  }
+  while (received_sig == -1) sleep(1);
+  EXPECT_EQ(received_sig, SIGUSR1);
+
+  // Manually block SIGPIPE; ScopedBlockSignals should not unblock this
+  sigset_t block_sigset;
+  sigemptyset(&block_sigset);
+  sigaddset(&block_sigset, SIGPIPE);
+  sigprocmask(SIG_BLOCK, &block_sigset, NULL);
+  {
+    __sanitizer_sigset_t sigset = {};
+    ScopedBlockSignals block(&sigset);
+
+    received_sig = -1;
+    signal(SIGPIPE, signal_handler);
+    raise(SIGPIPE);
+    sleep(1);
+    EXPECT_EQ(received_sig, -1);
+  }
+  sigprocmask(SIG_UNBLOCK, &block_sigset, NULL);
+  while (received_sig == -1) sleep(1);
+  EXPECT_EQ(received_sig, SIGPIPE);
+}
+#endif  // SANITIZER_LINUX
+
+}  // namespace __sanitizer