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/*
* Copyright (C) 2014 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include <android/log.h>
#include <dlfcn.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
namespace art {
class SignalAction {
public:
SignalAction() : claimed_(false) {
}
// Claim the signal and keep the action specified.
void Claim(const struct sigaction& action) {
action_ = action;
claimed_ = true;
}
// Unclaim the signal and restore the old action.
void Unclaim(int signal) {
claimed_ = false;
sigaction(signal, &action_, NULL); // Restore old action.
}
// Get the action associated with this signal.
const struct sigaction& GetAction() const {
return action_;
}
// Is the signal claimed?
bool IsClaimed() const {
return claimed_;
}
// Change the recorded action to that specified.
void SetAction(const struct sigaction& action) {
action_ = action;
}
private:
struct sigaction action_; // Action to be performed.
bool claimed_; // Whether signal is claimed or not.
};
// User's signal handlers
static SignalAction user_sigactions[_NSIG];
static void log(const char* format, ...) {
char buf[256];
va_list ap;
va_start(ap, format);
vsnprintf(buf, sizeof(buf), format, ap);
__android_log_write(ANDROID_LOG_ERROR, "libsigchain", buf);
va_end(ap);
}
static void CheckSignalValid(int signal) {
if (signal <= 0 || signal >= _NSIG) {
log("Invalid signal %d", signal);
abort();
}
}
// Claim a signal chain for a particular signal.
void ClaimSignalChain(int signal, struct sigaction* oldaction) {
CheckSignalValid(signal);
user_sigactions[signal].Claim(*oldaction);
}
void UnclaimSignalChain(int signal) {
CheckSignalValid(signal);
user_sigactions[signal].Unclaim(signal);
}
// Invoke the user's signal handler.
void InvokeUserSignalHandler(int sig, siginfo_t* info, void* context) {
// Check the arguments.
CheckSignalValid(sig);
// The signal must have been claimed in order to get here. Check it.
if (!user_sigactions[sig].IsClaimed()) {
abort();
}
const struct sigaction& action = user_sigactions[sig].GetAction();
if ((action.sa_flags & SA_SIGINFO) == 0) {
if (action.sa_handler != NULL) {
action.sa_handler(sig);
}
} else {
if (action.sa_sigaction != NULL) {
action.sa_sigaction(sig, info, context);
}
}
}
extern "C" {
// These functions are C linkage since they replace the functions in libc.
int sigaction(int signal, const struct sigaction* new_action, struct sigaction* old_action) {
// If this signal has been claimed as a signal chain, record the user's
// action but don't pass it on to the kernel.
// Note that we check that the signal number is in range here. An out of range signal
// number should behave exactly as the libc sigaction.
if (signal > 0 && signal < _NSIG && user_sigactions[signal].IsClaimed()) {
if (old_action != NULL) {
*old_action = user_sigactions[signal].GetAction();
}
if (new_action != NULL) {
user_sigactions[signal].SetAction(*new_action);
}
return 0;
}
// Will only get here if the signal chain has not been claimed. We want
// to pass the sigaction on to the kernel via the real sigaction in libc.
void* linked_sigaction_sym = dlsym(RTLD_NEXT, "sigaction");
if (linked_sigaction_sym == nullptr) {
log("Unable to find next sigaction in signal chain");
abort();
}
typedef int (*SigAction)(int, const struct sigaction*, struct sigaction*);
SigAction linked_sigaction = reinterpret_cast<SigAction>(linked_sigaction_sym);
return linked_sigaction(signal, new_action, old_action);
}
int sigprocmask(int how, const sigset_t* bionic_new_set, sigset_t* bionic_old_set) {
const sigset_t* new_set_ptr = bionic_new_set;
sigset_t tmpset;
if (bionic_new_set != NULL) {
tmpset = *bionic_new_set;
if (how == SIG_BLOCK) {
// Don't allow claimed signals in the mask. If a signal chain has been claimed
// we can't allow the user to block that signal.
for (int i = 0 ; i < _NSIG; ++i) {
if (user_sigactions[i].IsClaimed() && sigismember(&tmpset, i)) {
sigdelset(&tmpset, i);
}
}
}
new_set_ptr = &tmpset;
}
void* linked_sigprocmask_sym = dlsym(RTLD_NEXT, "sigprocmask");
if (linked_sigprocmask_sym == nullptr) {
log("Unable to find next sigprocmask in signal chain");
abort();
}
typedef int (*SigProcMask)(int how, const sigset_t*, sigset_t*);
SigProcMask linked_sigprocmask= reinterpret_cast<SigProcMask>(linked_sigprocmask_sym);
return linked_sigprocmask(how, new_set_ptr, bionic_old_set);
}
} // extern "C"
} // namespace art
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