[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Tue, 3 Mar 2020 17:50:34 +0100
From: Christian Brauner <christian.brauner@...ntu.com>
To: "Eric W. Biederman" <ebiederm@...ssion.com>
Cc: Bernd Edlinger <bernd.edlinger@...mail.de>,
Kees Cook <keescook@...omium.org>,
Jann Horn <jannh@...gle.com>, Jonathan Corbet <corbet@....net>,
Alexander Viro <viro@...iv.linux.org.uk>,
Andrew Morton <akpm@...ux-foundation.org>,
Alexey Dobriyan <adobriyan@...il.com>,
Thomas Gleixner <tglx@...utronix.de>,
Oleg Nesterov <oleg@...hat.com>,
Frederic Weisbecker <frederic@...nel.org>,
Andrei Vagin <avagin@...il.com>,
Ingo Molnar <mingo@...nel.org>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>,
Yuyang Du <duyuyang@...il.com>,
David Hildenbrand <david@...hat.com>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Anshuman Khandual <anshuman.khandual@....com>,
David Howells <dhowells@...hat.com>,
James Morris <jamorris@...ux.microsoft.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Shakeel Butt <shakeelb@...gle.com>,
Jason Gunthorpe <jgg@...pe.ca>,
Christian Kellner <christian@...lner.me>,
Andrea Arcangeli <aarcange@...hat.com>,
Aleksa Sarai <cyphar@...har.com>,
"Dmitry V. Levin" <ldv@...linux.org>,
"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
"stable@...r.kernel.org" <stable@...r.kernel.org>,
linux-api@...r.kernel.org
Subject: Re: [PATCHv5] exec: Fix a deadlock in ptrace
On Tue, Mar 03, 2020 at 09:18:44AM -0600, Eric W. Biederman wrote:
> Bernd Edlinger <bernd.edlinger@...mail.de> writes:
>
> > This fixes a deadlock in the tracer when tracing a multi-threaded
> > application that calls execve while more than one thread are running.
> >
> > I observed that when running strace on the gcc test suite, it always
> > blocks after a while, when expect calls execve, because other threads
> > have to be terminated. They send ptrace events, but the strace is no
> > longer able to respond, since it is blocked in vm_access.
> >
> > The deadlock is always happening when strace needs to access the
> > tracees process mmap, while another thread in the tracee starts to
> > execve a child process, but that cannot continue until the
> > PTRACE_EVENT_EXIT is handled and the WIFEXITED event is received:
>
> A couple of things.
>
> Why do we think it is safe to change the behavior exposed to userspace?
> Not the deadlock but all of the times the current code would not
> deadlock?
>
> Especially given that this is a small window it might be hard for people
> to track down and report so we need a strong argument that this won't
> break existing userspace before we just change things.
>
> Usually surveying all of the users of a system call that we can find
> and checking to see if they might be affected by the change in behavior
> is difficult enough that we usually opt for not being lazy and
> preserving the behavior.
>
> This patch is up to two changes in behavior now, that could potentially
> affect a whole array of programs. Adding linux-api so that this change
> in behavior can be documented if/when this change goes through.
>
> If you can split the documentation and test fixes out into separate
> patches that would help reviewing this code, or please make it explicit
> that the your are changing documentation about behavior that is changing
> with this patch.
Agreed. I think it'd be good to do it in three patches:
1. unrelated documentation update
2. fix + documentation changes specific to the fix
3. test(s)
Christian
Powered by blists - more mailing lists