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Commit fd13bf0d authored by Josh Gao's avatar Josh Gao
Browse files

crash_dump: print the identity of tracers. 

Instead of printing a useless "ptrace attach failed: strerror(EPERM)"
message, print the name and pid of a competing tracer when we fail to
attach because a process is already being ptraced.

Bug: http://b/31531918
Test: debuggerd_test32, debuggerd_test64 on aosp_angler
Test: strace -p `pidof surfaceflinger`; debuggerd -b surfaceflinger
Change-Id: Ifd3f80fe03de30ff38c0e0068560a7b12875f29d
parent de6b44aa

debuggerd/crash_dump.cpp

+18 −0
Original line number Diff line number Diff line
@@ -79,9 +79,27 @@ static bool pid_contains_tid(int pid_proc_fd, pid_t tid) { 
  return fstatat(pid_proc_fd, task_path.c_str(), &st, 0) == 0;

}



static pid_t get_tracer(pid_t tracee) {

  // Check to see if the thread is being ptraced by another process.

  android::procinfo::ProcessInfo process_info;

  if (android::procinfo::GetProcessInfo(tracee, &process_info)) {

    return process_info.tracer;

  }

  return -1;

}



// Attach to a thread, and verify that it's still a member of the given process

static bool ptrace_seize_thread(int pid_proc_fd, pid_t tid, std::string* error) {

  if (ptrace(PTRACE_SEIZE, tid, 0, 0) != 0) {

    if (errno == EPERM) {

      pid_t tracer = get_tracer(tid);

      if (tracer != -1) {

        *error = StringPrintf("failed to attach to thread %d, already traced by %d (%s)", tid,

                              tracer, get_process_name(tracer).c_str());

        return false;

      }

    }



    *error = StringPrintf("failed to attach to thread %d: %s", tid, strerror(errno));

    return false;

  }

debuggerd/debuggerd_test.cpp

+36 −1
Original line number Diff line number Diff line
@@ -16,10 +16,11 @@ 


#include <err.h>

#include <fcntl.h>

#include <unistd.h>

#include <sys/capability.h>

#include <sys/prctl.h>

#include <sys/ptrace.h>

#include <sys/types.h>

#include <unistd.h>



#include <chrono>

#include <regex>
@@ -569,6 +570,40 @@ TEST_F(CrasherTest, fake_pid) { 
  ASSERT_BACKTRACE_FRAME(result, "tgkill");

}



TEST_F(CrasherTest, competing_tracer) {

  int intercept_result;

  unique_fd output_fd;

  StartProcess([]() {

    while (true) {

    }

  });



  StartIntercept(&output_fd);

  FinishCrasher();



  ASSERT_EQ(0, ptrace(PTRACE_SEIZE, crasher_pid, 0, 0));

  ASSERT_EQ(0, kill(crasher_pid, SIGABRT));



  int status;

  ASSERT_EQ(crasher_pid, waitpid(crasher_pid, &status, 0));

  ASSERT_TRUE(WIFSTOPPED(status));

  ASSERT_EQ(SIGABRT, WSTOPSIG(status));



  ASSERT_EQ(0, ptrace(PTRACE_CONT, crasher_pid, 0, SIGABRT));

  FinishIntercept(&intercept_result);

  ASSERT_EQ(1, intercept_result) << "tombstoned reported failure";



  std::string result;

  ConsumeFd(std::move(output_fd), &result);

  std::string regex = R"(failed to attach to thread \d+, already traced by )";

  regex += std::to_string(gettid());

  regex += R"( \(.+debuggerd_test)";

  ASSERT_MATCH(result, regex.c_str());



  ASSERT_EQ(0, ptrace(PTRACE_DETACH, crasher_pid, 0, SIGABRT));

  AssertDeath(SIGABRT);

}



TEST(crash_dump, zombie) {

  pid_t forkpid = fork();