From: Greg KH <gregkh@linuxfoundation.org>
To: Bernd Edlinger <bernd.edlinger@hotmail.de>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Alexey Dobriyan <adobriyan@gmail.com>,
Oleg Nesterov <oleg@redhat.com>,
Kees Cook <keescook@chromium.org>,
Andy Lutomirski <luto@amacapital.net>,
Will Drewry <wad@chromium.org>, Shuah Khan <shuah@kernel.org>,
Christian Brauner <christian.brauner@ubuntu.com>,
Michal Hocko <mhocko@suse.com>, Serge Hallyn <serge@hallyn.com>,
James Morris <jamorris@linux.microsoft.com>,
"Eric W. Biederman" <ebiederm@xmission.com>,
Charles Haithcock <chaithco@redhat.com>,
Suren Baghdasaryan <surenb@google.com>,
Yafang Shao <laoar.shao@gmail.com>, Helge Deller <deller@gmx.de>,
YiFei Zhu <yifeifz2@illinois.edu>,
Adrian Reber <areber@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
Jens Axboe <axboe@kernel.dk>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
linux-kselftest@vger.kernel.org,
"stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: Re: [PATCH v9] exec: Fix dead-lock in de_thread with ptrace_attach
Date: Sat, 12 Jun 2021 09:02:43 +0200 [thread overview]
Message-ID: <YMRcE8NXspQjSwQZ@kroah.com> (raw)
In-Reply-To: <AM8PR10MB470896FBC519ABCC20486958E4349@AM8PR10MB4708.EURPRD10.PROD.OUTLOOK.COM>
On Fri, Jun 11, 2021 at 05:55:09PM +0200, Bernd Edlinger wrote:
> This introduces signal->unsafe_execve_in_progress,
> which is used to fix the case when at least one of the
> sibling threads is traced, and therefore the trace
> process may dead-lock in ptrace_attach, but de_thread
> will need to wait for the tracer to continue execution.
>
> The solution is to detect this situation and allow
> ptrace_attach to continue, while de_thread() is still
> waiting for traced zombies to be eventually released.
> When the current thread changed the ptrace status from
> non-traced to traced, we can simply abort the whole
> execve and restart it by returning -ERESTARTSYS.
> This needs to be done before changing the thread leader,
> because the PTRACE_EVENT_EXEC needs to know the old
> thread pid.
>
> Although it is technically after the point of no return,
> we just have to reset bprm->point_of_no_return here,
> since at this time only the other threads have received
> a fatal signal, not the current thread.
>
> >From the user's point of view the whole execve was
> simply delayed until after the ptrace_attach.
>
> Other threads die quickly since the cred_guard_mutex
> is released, but a deadly signal is already pending.
> In case the mutex_lock_killable misses the signal,
> ->unsafe_execve_in_progress makes sure they release
> the mutex immediately and return with -ERESTARTNOINTR.
>
> This means there is no API change, unlike the previous
> version of this patch which was discussed here:
>
> https://lore.kernel.org/lkml/b6537ae6-31b1-5c50-f32b-8b8332ace882@hotmail.de/
>
> See tools/testing/selftests/ptrace/vmaccess.c
> for a test case that gets fixed by this change.
>
> Note that since the test case was originally designed to
> test the ptrace_attach returning an error in this situation,
> the test expectation needed to be adjusted, to allow the
> API to succeed at the first attempt.
>
> Signed-off-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
> ---
> fs/exec.c | 37 +++++++++++++++++++++++++++++--
> fs/proc/base.c | 6 +++++
> include/linux/sched/signal.h | 13 +++++++++++
> kernel/ptrace.c | 9 ++++++++
> kernel/seccomp.c | 12 +++++++---
> tools/testing/selftests/ptrace/vmaccess.c | 25 ++++++++++++++-------
> 6 files changed, 89 insertions(+), 13 deletions(-)
>
<formletter>
This is not the correct way to submit patches for inclusion in the
stable kernel tree. Please read:
https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.
</formletter>
next prev parent reply other threads:[~2021-06-12 7:03 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-10 7:31 [PATCHv8] exec: Fix dead-lock in de_thread with ptrace_attach Bernd Edlinger
2021-06-10 21:36 ` Andrew Morton
2021-06-11 4:42 ` Bernd Edlinger
2021-06-11 15:55 ` [PATCH v9] " Bernd Edlinger
2021-06-11 23:16 ` Andrew Morton
2021-06-12 5:22 ` Bernd Edlinger
2021-06-12 7:02 ` Greg KH [this message]
2021-06-14 16:42 ` Eric W. Biederman
2021-06-15 14:26 ` Bernd Edlinger
2021-06-16 21:31 ` Bernd Edlinger
2021-06-22 5:10 ` Bernd Edlinger
2021-06-12 19:44 ` [PATCHv8] " Eric W. Biederman
2021-06-11 7:54 ` Bernd Edlinger
2021-06-11 23:15 ` Andrew Morton
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