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Commit d2069632 authored by Josh Gao's avatar Josh Gao
Browse files

debuggerd_handler: raise capabilities before running crash_dump. 

Raise CapInh and CapAmb after forking to exec crash_dump, so that it
can ptrace us.

Bug: http://b/35174939
Test: debuggerd -b `pidof surfaceflinger`
Change-Id: I32567010a3603cfa494aae9dc0e3ce73fb86b590
parent 91ad653c

debuggerd/handler/debuggerd_handler.cpp

+36 −4
Original line number Diff line number Diff line
@@ -174,6 +174,41 @@ static bool have_siginfo(int signum) { 
  return (old_action.sa_flags & SA_SIGINFO) != 0;

}



static void raise_caps() {

  // Raise CapInh to match CapPrm, so that we can set the ambient bits.

  __user_cap_header_struct capheader;

  memset(&capheader, 0, sizeof(capheader));

  capheader.version = _LINUX_CAPABILITY_VERSION_3;

  capheader.pid = 0;



  __user_cap_data_struct capdata[2];

  if (capget(&capheader, &capdata[0]) == -1) {

    fatal_errno("capget failed");

  }



  if (capdata[0].permitted != capdata[0].inheritable ||

      capdata[1].permitted != capdata[1].inheritable) {

    capdata[0].inheritable = capdata[0].permitted;

    capdata[1].inheritable = capdata[1].permitted;



    if (capset(&capheader, &capdata[0]) == -1) {

      __libc_format_log(ANDROID_LOG_ERROR, "libc", "capset failed: %s", strerror(errno));

    }

  }



  // Set the ambient capability bits so that crash_dump gets all of our caps and can ptrace us.

  uint64_t capmask = capdata[0].inheritable;

  capmask |= static_cast<uint64_t>(capdata[1].inheritable) << 32;

  for (unsigned long i = 0; i < 64; ++i) {

    if (capmask & (1 << i)) {

      if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, i, 0, 0) != 0) {

        __libc_format_log(ANDROID_LOG_ERROR, "libc", "failed to raise ambient capability %lu: %s",

                          i, strerror(errno));

      }

    }

  }

}



struct debugger_thread_info {

  bool crash_dump_started;

  pid_t crashing_tid;
@@ -217,10 +252,7 @@ static int debuggerd_dispatch_pseudothread(void* arg) { 
    close(pipefds[0]);

    close(pipefds[1]);



    // Set all of the ambient capability bits we can, so that crash_dump can ptrace us.

    for (unsigned long i = 0; prctl(PR_CAPBSET_READ, i, 0, 0, 0) != -1; ++i) {

      prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, i, 0, 0);

    }

    raise_caps();



    char buf[10];

    snprintf(buf, sizeof(buf), "%d", thread_info->crashing_tid);