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/*
* Copyright (c) 2020, Ben Wiederhake <BenWiederhake.GitHub@gmx.de>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <assert.h>
#include <pthread.h>
#include <signal.h>
#include <stdio.h>
#include <time.h>
#include <unistd.h>
static void signal_printer(int)
{
// no-op
}
typedef struct yank_shared_t {
timespec* remaining_sleep;
// TODO: Be nice and use thread ID
//pthread_t sleeper_thread;
} yank_shared_t;
static void* yanker_fn(void* shared_)
{
yank_shared_t* shared = static_cast<yank_shared_t*>(shared_);
timespec requested_sleep = { 1, 0 };
int rc = clock_nanosleep(CLOCK_MONOTONIC, 0, &requested_sleep, nullptr);
if (rc != 0) {
printf("Yanker: Failed during sleep: %d\n", rc);
return nullptr;
}
delete shared->remaining_sleep; // T2
// Send SIGUSR1.
// Use pthread:
// pthread_kill(somewhere, SIGUSR1);
// But wait! pthread_kill isn't implemented yet, and therefore causes
// a linker error. It also looks like the corresponding syscall is missing.
// Use normal IPC syscall:
// kill(getpid(), SIGUSR1);
// But wait! If destination_pid == own_pid, then the signal is sent
// to the calling thread, *no matter what*.
// So, we have to go the very ugly route of fork():
// (Thank goodness this is only a demo of a kernel bug!)
pid_t pid_to_kill = getpid();
pid_t child_pid = fork();
if (child_pid < 0) {
printf("Yanker: Fork failed: %d\n", child_pid);
pthread_exit(nullptr); // See below
}
if (child_pid > 0) {
// Success. Terminate quickly. T3
// FIXME: LibPthread bug: returning during normal operation causes nullptr deref.
// Workaround: Exit manually.
pthread_exit(nullptr);
}
// Give parent *thread* a moment to die.
requested_sleep = { 1, 0 };
rc = clock_nanosleep(CLOCK_MONOTONIC, 0, &requested_sleep, nullptr);
if (rc != 0) {
printf("Yanker-child: Failed during sleep: %d\n", rc);
return nullptr;
}
// Prod the parent *process*
kill(pid_to_kill, SIGUSR1); // T4
// Wait a moment, to ensure the log output is as well-separated as possible.
requested_sleep = { 2, 0 };
rc = clock_nanosleep(CLOCK_MONOTONIC, 0, &requested_sleep, nullptr);
if (rc != 0) {
printf("Yanker-child: Failed during after-sleep: %d\n", rc);
return nullptr;
}
pthread_exit(nullptr);
assert(false);
// FIXME: return nullptr;
}
int main()
{
// Chronological order:
// T0: Main thread allocates region for the outvalue of clock_nanosleep
// T1: Main thread enters clock_nanosleep
// T2: Side thread deallocates that region
// T3: Side thread dies
// T4: A different process sends SIGUSR1, waking up the main thread,
// forcing the kernel to write to the deallocated Region.
// I'm sorry that both a side *thread* and a side *process* are necessary.
// Maybe in the future this test can be simplified, see above.
yank_shared_t shared = { nullptr };
shared.remaining_sleep = new timespec({ 0xbad, 0xf00d }); // T0
pthread_t yanker_thread;
int rc = pthread_create(&yanker_thread, nullptr, yanker_fn, &shared);
if (rc != 0) {
perror("pthread");
printf("FAIL\n");
return 1;
}
// Set an action for SIGUSR1, so that the sleep can be interrupted:
signal(SIGUSR1, signal_printer);
// T1: Go to sleep.
const timespec requested_sleep = { 3, 0 };
rc = clock_nanosleep(CLOCK_MONOTONIC, 0, &requested_sleep, shared.remaining_sleep);
// Now we are beyond T4.
if (rc == 0) {
// We somehow weren't interrupted. Bad.
printf("Not interrupted.\n");
printf("FAIL\n");
return 1;
}
// nanosleep was interrupted and the kernel didn't crash. Good!
printf("PASS\n");
return 0;
}
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