Re: [PATCH] ptrace: clear TIF_SYSCALL_TRACE on ptrace detach

From	Oleg Nesterov <oleg@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] ptrace: clear TIF_SYSCALL_TRACE on ptrace detach
Date	2016-09-02 14:30 +0200
Message-ID	<scVLA-7Si-31@gated-at.bofh.it> (permalink)
References	<scDlE-4lf-57@gated-at.bofh.it> <scHph-70l-81@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On 09/01, Ales Novak wrote:
>
> On __ptrace_detach(), called from do_exit()->exit_notify()->
> forget_original_parent()->exit_ptrace(), the TIF_SYSCALL_TRACE in
> thread->flags of the tracee is not cleared up. This results in the
> tracehook_report_syscall_* being called (though there's no longer a
> tracer listening to that) upon its further syscalls.
>
> Example scenario - attach "strace" to a running process and kill it (the
> strace) with SIGKILL. You'll see that the syscall trace hooks are still
> being called.

To clarify, this patch can't really fix the problem(s), The tracee can
be killed by SIGTRAP in this case. Again, we do not care too much, a lot
of bad things can happen if the tracer dies.

But I agree, this patch makes the things better for free,

Acked-by: Oleg Nesterov <oleg@redhat.com>

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[PATCH] ptrace: clear TIF_SYSCALL_TRACE on ptrace detach Ales Novak <alnovak@suse.cz> - 2016-09-01 16:00 +0200
  Re: [PATCH] ptrace: clear TIF_SYSCALL_TRACE on ptrace detach Oleg Nesterov <oleg@redhat.com> - 2016-09-01 18:50 +0200
    Re: [PATCH] ptrace: clear TIF_SYSCALL_TRACE on ptrace detach Ales Novak <alnovak@suse.cz> - 2016-09-01 23:10 +0200
    [PATCH] ptrace: clear TIF_SYSCALL_TRACE on ptrace detach Ales Novak <alnovak@suse.cz> - 2016-09-01 23:10 +0200
      Re: [PATCH] ptrace: clear TIF_SYSCALL_TRACE on ptrace detach Oleg Nesterov <oleg@redhat.com> - 2016-09-02 14:30 +0200

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