diff options
author | Oleg Nesterov <oleg@redhat.com> | 2020-11-01 17:07:44 -0800 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2020-11-02 12:14:19 -0800 |
commit | 7b3c36fc4c231ca532120bbc0df67a12f09c1d96 (patch) | |
tree | 97f811ce147ad66596c6506941812256cf1e5f28 | |
parent | 3f08842098e842c51e3b97d0dcdebf810b32558e (diff) | |
download | linux-7b3c36fc4c231ca532120bbc0df67a12f09c1d96.tar.bz2 |
ptrace: fix task_join_group_stop() for the case when current is traced
This testcase
#include <stdio.h>
#include <unistd.h>
#include <signal.h>
#include <sys/ptrace.h>
#include <sys/wait.h>
#include <pthread.h>
#include <assert.h>
void *tf(void *arg)
{
return NULL;
}
int main(void)
{
int pid = fork();
if (!pid) {
kill(getpid(), SIGSTOP);
pthread_t th;
pthread_create(&th, NULL, tf, NULL);
return 0;
}
waitpid(pid, NULL, WSTOPPED);
ptrace(PTRACE_SEIZE, pid, 0, PTRACE_O_TRACECLONE);
waitpid(pid, NULL, 0);
ptrace(PTRACE_CONT, pid, 0,0);
waitpid(pid, NULL, 0);
int status;
int thread = waitpid(-1, &status, 0);
assert(thread > 0 && thread != pid);
assert(status == 0x80137f);
return 0;
}
fails and triggers WARN_ON_ONCE(!signr) in do_jobctl_trap().
This is because task_join_group_stop() has 2 problems when current is traced:
1. We can't rely on the "JOBCTL_STOP_PENDING" check, a stopped tracee
can be woken up by debugger and it can clone another thread which
should join the group-stop.
We need to check group_stop_count || SIGNAL_STOP_STOPPED.
2. If SIGNAL_STOP_STOPPED is already set, we should not increment
sig->group_stop_count and add JOBCTL_STOP_CONSUME. The new thread
should stop without another do_notify_parent_cldstop() report.
To clarify, the problem is very old and we should blame
ptrace_init_task(). But now that we have task_join_group_stop() it makes
more sense to fix this helper to avoid the code duplication.
Reported-by: syzbot+3485e3773f7da290eecc@syzkaller.appspotmail.com
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Christian Brauner <christian@brauner.io>
Cc: "Eric W . Biederman" <ebiederm@xmission.com>
Cc: Zhiqiang Liu <liuzhiqiang26@huawei.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: <stable@vger.kernel.org>
Link: https://lkml.kernel.org/r/20201019134237.GA18810@redhat.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r-- | kernel/signal.c | 19 |
1 files changed, 10 insertions, 9 deletions
diff --git a/kernel/signal.c b/kernel/signal.c index a38b3edc6851..ef8f2a28d37c 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -391,16 +391,17 @@ static bool task_participate_group_stop(struct task_struct *task) void task_join_group_stop(struct task_struct *task) { + unsigned long mask = current->jobctl & JOBCTL_STOP_SIGMASK; + struct signal_struct *sig = current->signal; + + if (sig->group_stop_count) { + sig->group_stop_count++; + mask |= JOBCTL_STOP_CONSUME; + } else if (!(sig->flags & SIGNAL_STOP_STOPPED)) + return; + /* Have the new thread join an on-going signal group stop */ - unsigned long jobctl = current->jobctl; - if (jobctl & JOBCTL_STOP_PENDING) { - struct signal_struct *sig = current->signal; - unsigned long signr = jobctl & JOBCTL_STOP_SIGMASK; - unsigned long gstop = JOBCTL_STOP_PENDING | JOBCTL_STOP_CONSUME; - if (task_set_jobctl_pending(task, signr | gstop)) { - sig->group_stop_count++; - } - } + task_set_jobctl_pending(task, mask | JOBCTL_STOP_PENDING); } /* |