linux-kernel - Re: [PATCH v14] exec: Fix dead-lock in de_thread with ptrace

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Message-ID: <202401231555.59B7EDBB2@keescook>
Date: Tue, 23 Jan 2024 16:09:12 -0800
From: Kees Cook <keescook@...omium.org>
To: Bernd Edlinger <bernd.edlinger@...mail.de>
Cc: Oleg Nesterov <oleg@...hat.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Andy Lutomirski <luto@...capital.net>,
	Will Drewry <wad@...omium.org>,
	Christian Brauner <brauner@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.com>, Serge Hallyn <serge@...lyn.com>,
	James Morris <jamorris@...ux.microsoft.com>,
	Randy Dunlap <rdunlap@...radead.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Yafang Shao <laoar.shao@...il.com>, Helge Deller <deller@....de>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Adrian Reber <areber@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>, Jens Axboe <axboe@...nel.dk>,
	Alexei Starovoitov <ast@...nel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-kselftest@...r.kernel.org, linux-mm@...ck.org,
	tiozhang <tiozhang@...iglobal.com>,
	Luis Chamberlain <mcgrof@...nel.org>,
	"Paulo Alcantara (SUSE)" <pc@...guebit.com>,
	Sergey Senozhatsky <senozhatsky@...omium.org>,
	Frederic Weisbecker <frederic@...nel.org>,
	YueHaibing <yuehaibing@...wei.com>,
	Paul Moore <paul@...l-moore.com>, Aleksa Sarai <cyphar@...har.com>,
	Stefan Roesch <shr@...kernel.io>, Chao Yu <chao@...nel.org>,
	xu xin <xu.xin16@....com.cn>, Jeff Layton <jlayton@...nel.org>,
	Jan Kara <jack@...e.cz>, David Hildenbrand <david@...hat.com>,
	Dave Chinner <dchinner@...hat.com>, Shuah Khan <shuah@...nel.org>,
	Zheng Yejian <zhengyejian1@...wei.com>,
	Elena Reshetova <elena.reshetova@...el.com>,
	David Windsor <dwindsor@...il.com>,
	Mateusz Guzik <mjguzik@...il.com>, Ard Biesheuvel <ardb@...nel.org>,
	"Joel Fernandes (Google)" <joel@...lfernandes.org>,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>,
	Hans Liljestrand <ishkamiel@...il.com>
Subject: Re: [PATCH v14] exec: Fix dead-lock in de_thread with ptrace_attach

On Tue, Jan 23, 2024 at 07:30:52PM +0100, Bernd Edlinger wrote:
> - Currently a non-privileged program can potentially send such a privileged
> tracer into a deadlock.
> - With the alternative patch below that non-privileged can no longer send the
> tracer into a deadlock, but it can still quickly escape out of the tracer's
> control.
> - But with my latest patch a sufficiently privileged tracer can neither be
> sent into a deadlock nor can the attached process escape.  Mission completed.

Thanks for the details. And it would be pretty unfriendly to fail the execve()
too (or, rather, it makes the execve failure unpredictable). I'll keep
reading your patch...

-- 
Kees Cook