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Date:   Thu, 10 Jun 2021 14:36:42 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Bernd Edlinger <bernd.edlinger@hotmail.de>
Cc:     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
Subject: Re: [PATCHv8] exec: Fix dead-lock in de_thread with ptrace_attach
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On Thu, 10 Jun 2021 09:31:42 +0200 Bernd Edlinger <bernd.edlinger@hotmail.de> 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.

Deadlocks are serious.  Is this exploitable by unprivileged userspace?

> Signed-off-by: Bernd Edlinger <bernd.edlinger@hotmail.de>

Was a -stable backport considered?