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      1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #include "sandbox/linux/seccomp-bpf/die.h"
      6 
      7 #include <errno.h>
      8 #include <signal.h>
      9 #include <stdio.h>
     10 #include <sys/prctl.h>
     11 #include <sys/syscall.h>
     12 #include <unistd.h>
     13 
     14 #include <string>
     15 
     16 #include "base/logging.h"
     17 #include "base/posix/eintr_wrapper.h"
     18 #include "sandbox/linux/seccomp-bpf/syscall.h"
     19 #include "sandbox/linux/services/syscall_wrappers.h"
     20 #include "sandbox/linux/system_headers/linux_signal.h"
     21 
     22 namespace sandbox {
     23 
     24 void Die::ExitGroup() {
     25   // exit_group() should exit our program. After all, it is defined as a
     26   // function that doesn't return. But things can theoretically go wrong.
     27   // Especially, since we are dealing with system call filters. Continuing
     28   // execution would be very bad in most cases where ExitGroup() gets called.
     29   // So, we'll try a few other strategies too.
     30   Syscall::Call(__NR_exit_group, 1);
     31 
     32   // We have no idea what our run-time environment looks like. So, signal
     33   // handlers might or might not do the right thing. Try to reset settings
     34   // to a defined state; but we have not way to verify whether we actually
     35   // succeeded in doing so. Nonetheless, triggering a fatal signal could help
     36   // us terminate.
     37   struct sigaction sa = {};
     38   sa.sa_handler = LINUX_SIG_DFL;
     39   sa.sa_flags = LINUX_SA_RESTART;
     40   sys_sigaction(LINUX_SIGSEGV, &sa, nullptr);
     41   Syscall::Call(__NR_prctl, PR_SET_DUMPABLE, (void*)0, (void*)0, (void*)0);
     42   if (*(volatile char*)0) {
     43   }
     44 
     45   // If there is no way for us to ask for the program to exit, the next
     46   // best thing we can do is to loop indefinitely. Maybe, somebody will notice
     47   // and file a bug...
     48   // We in fact retry the system call inside of our loop so that it will
     49   // stand out when somebody tries to diagnose the problem by using "strace".
     50   for (;;) {
     51     Syscall::Call(__NR_exit_group, 1);
     52   }
     53 }
     54 
     55 void Die::SandboxDie(const char* msg, const char* file, int line) {
     56   if (simple_exit_) {
     57     LogToStderr(msg, file, line);
     58   } else {
     59     logging::LogMessage(file, line, logging::LOG_FATAL).stream() << msg;
     60   }
     61   ExitGroup();
     62 }
     63 
     64 void Die::RawSandboxDie(const char* msg) {
     65   if (!msg)
     66     msg = "";
     67   RAW_LOG(FATAL, msg);
     68   ExitGroup();
     69 }
     70 
     71 void Die::SandboxInfo(const char* msg, const char* file, int line) {
     72   if (!suppress_info_) {
     73     logging::LogMessage(file, line, logging::LOG_INFO).stream() << msg;
     74   }
     75 }
     76 
     77 void Die::LogToStderr(const char* msg, const char* file, int line) {
     78   if (msg) {
     79     char buf[40];
     80     snprintf(buf, sizeof(buf), "%d", line);
     81     std::string s = std::string(file) + ":" + buf + ":" + msg + "\n";
     82 
     83     // No need to loop. Short write()s are unlikely and if they happen we
     84     // probably prefer them over a loop that blocks.
     85     ignore_result(
     86         HANDLE_EINTR(Syscall::Call(__NR_write, 2, s.c_str(), s.length())));
     87   }
     88 }
     89 
     90 bool Die::simple_exit_ = false;
     91 bool Die::suppress_info_ = false;
     92 
     93 }  // namespace sandbox
     94