content/common/sandbox_linux/sandbox_debug_handling_linux.cc

   1 // Copyright 2015 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 "content/common/sandbox_linux/sandbox_debug_handling_linux.h"
   6
   7 #include <errno.h>
   8 #include <signal.h>
   9 #include <sys/prctl.h>
  10 #include <unistd.h>
  11
  12 #include "base/command_line.h"
  13 #include "base/logging.h"
  14 #include "base/macros.h"
  15 #include "base/strings/safe_sprintf.h"
  16 #include "content/public/common/content_switches.h"
  17
  18 namespace content {
  19
  20 namespace {
  21
  22 void DoChrootSignalHandler(int) {
  23   const int old_errno = errno;
  24   const char kFirstMessage[] = "Chroot signal handler called.\n";
  25   ignore_result(write(STDERR_FILENO, kFirstMessage, sizeof(kFirstMessage) - 1));
  26
  27   const int chroot_ret = chroot("/");
  28
  29   char kSecondMessage[100];
  30   const ssize_t printed = base::strings::SafeSPrintf(
  31       kSecondMessage, "chroot() returned %d. Errno is %d.\n", chroot_ret,
  32       errno);
  33   if (printed > 0 && printed < static_cast<ssize_t>(sizeof(kSecondMessage))) {
  34     ignore_result(write(STDERR_FILENO, kSecondMessage, printed));
  35   }
  36   errno = old_errno;
  37 }
  38
  39 // This is a quick hack to allow testing sandbox crash reports in production
  40 // binaries.
  41 // This installs a signal handler for SIGUSR2 that performs a chroot().
  42 // In most of our BPF policies, it is a "watched" system call which will
  43 // trigger a SIGSYS signal whose handler will crash.
  44 // This has been added during the investigation of https://crbug.com/415842.
  45 void InstallCrashTestHandler() {
  46   struct sigaction act = {};
  47   act.sa_handler = DoChrootSignalHandler;
  48   CHECK_EQ(0, sigemptyset(&act.sa_mask));
  49   act.sa_flags = 0;
  50
  51   PCHECK(0 == sigaction(SIGUSR2, &act, NULL));
  52 }
  53
  54 bool IsSandboxDebuggingEnabled() {
  55   const base::CommandLine& command_line =
  56       *base::CommandLine::ForCurrentProcess();
  57   return command_line.HasSwitch(switches::kAllowSandboxDebugging);
  58 }
  59
  60 }  // namespace
  61
  62 // static
  63 bool SandboxDebugHandling::SetDumpableStatusAndHandlers() {
  64   if (IsSandboxDebuggingEnabled()) {
  65     // If sandbox debugging is allowed, install a handler for sandbox-related
  66     // crash testing.
  67     InstallCrashTestHandler();
  68     return true;
  69   }
  70
  71   if (prctl(PR_SET_DUMPABLE, 0) != 0) {
  72     PLOG(ERROR) << "Failed to set non-dumpable flag";
  73     return false;
  74   }
  75
  76   return prctl(PR_GET_DUMPABLE) == 0;
  77 }
  78
  79 }  // namespace content