From: ebiederm@xmission.com (Eric W. Biederman)
To: Bernd Edlinger <bernd.edlinger@hotmail.de>
Cc: Christian Brauner <christian.brauner@ubuntu.com>,
Kees Cook <keescook@chromium.org>, Jann Horn <jannh@google.com>,
Jonathan Corbet <corbet@lwn.net>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Andrew Morton <akpm@linux-foundation.org>,
Alexey Dobriyan <adobriyan@gmail.com>,
Thomas Gleixner <tglx@linutronix.de>,
Oleg Nesterov <oleg@redhat.com>,
Frederic Weisbecker <frederic@kernel.org>,
Andrei Vagin <avagin@gmail.com>, Ingo Molnar <mingo@kernel.org>,
"Peter Zijlstra \(Intel\)" <peterz@infradead.org>,
Yuyang Du <duyuyang@gmail.com>,
David Hildenbrand <david@redhat.com>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Anshuman Khandual <anshuman.khandual@arm.com>,
David Howells <dhowells@redhat.com>,
James Morris <jamorris@linux.microsoft.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Shakeel Butt <shakeelb@google.com>,
Jason Gunthorpe <jgg@ziepe.ca>,
Christian Kellner <christian@kellner.me>,
Andrea Arcangeli <aarcange@redhat.com>,
Aleksa Sarai <cyphar@cyphar.com>,
"Dmitry V. Levin" <ldv@altlinux.org>,
"linux-doc\@vger.kernel.org" <linux-doc@vger.kernel.org>,
"linux-kernel\@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-fsdevel\@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
"linux-mm\@kvack.org" <linux-mm@kvack.org>,
"stable\@vger.kernel.org" <stable@vger.kernel.org>,
"linux-api\@vger.kernel.org" <linux-api@vger.kernel.org>
Subject: Re: [PATCH 2/2] exec: Add a exec_update_mutex to replace cred_guard_mutex
Date: Fri, 06 Mar 2020 16:29:39 -0600 [thread overview]
Message-ID: <87a74t86cs.fsf@x220.int.ebiederm.org> (raw)
In-Reply-To: <87sgil87s3.fsf@x220.int.ebiederm.org> (Eric W. Biederman's message of "Fri, 06 Mar 2020 15:58:52 -0600")
ebiederm@xmission.com (Eric W. Biederman) writes:
> Bernd Edlinger <bernd.edlinger@hotmail.de> writes:
>
>> On 3/6/20 6:17 AM, Eric W. Biederman wrote:
>>> Bernd Edlinger <bernd.edlinger@hotmail.de> writes:
>>>
>>>> On 3/5/20 10:16 PM, Eric W. Biederman wrote:
>>>>>
>>>>> The cred_guard_mutex is problematic. The cred_guard_mutex is held
>>>>> over the userspace accesses as the arguments from userspace are read.
>>>>> The cred_guard_mutex is held of PTRACE_EVENT_EXIT as the the other
>>>>> threads are killed. The cred_guard_mutex is held over
>>>>> "put_user(0, tsk->clear_child_tid)" in exit_mm().
>>>>>
>>
>> I am all for this patch, and the direction it is heading, Eric.
>>
>> I just wanted to add a note that I think it is
>> possible that exec_mm_release can also invoke put_user(0, tsk->clear_child_tid),
>> under the new exec_update_mutex, since vm_access increments the
>> mm->mm_users, under the cred_update_mutex, but releases the mutex,
>> and the caller can hold the reference for a while and then exec_mmap is not
>> releasing the last reference.
>
> Good catch. I really appreciate your close look at the details.
>
> I am wondering if process_vm_readv and process_vm_writev could be
> safely changed to use mmgrab and mmdrop, instead of mmget and mmput.
>
> That would resolve the potential issue you have pointed out. I just
> haven't figured out if it is safe. The mm code has been seriously
> refactored since I knew how it all worked.
Nope, mmget can not be replaced by mmgrab.
It might be possible to do something creative like store a cred in place
of the userns on the mm and use that for mm_access permission checks.
Still we are talking a pretty narrow window, and a case that no one has
figured out how to trigger yet. So I will leave that corner case as
something for future improvements.
Eric
next prev parent reply other threads:[~2020-03-06 22:32 UTC|newest]
Thread overview: 205+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-01 11:27 [PATCH] exec: Fix a deadlock in ptrace Bernd Edlinger
2020-03-01 15:13 ` Aleksa Sarai
2020-03-01 15:58 ` Christian Brauner
2020-03-01 17:46 ` Bernd Edlinger
2020-03-01 18:20 ` Christian Brauner
2020-03-01 17:24 ` Bernd Edlinger
2020-03-01 18:21 ` Jann Horn
2020-03-01 18:52 ` Christian Brauner
2020-03-01 19:00 ` Bernd Edlinger
2020-03-01 20:00 ` Jann Horn
2020-03-01 20:34 ` [PATCHv2] " Bernd Edlinger
2020-03-02 6:38 ` Eric W. Biederman
2020-03-02 15:43 ` Bernd Edlinger
2020-03-02 15:57 ` Eric W. Biederman
2020-03-02 16:02 ` Bernd Edlinger
2020-03-02 16:17 ` Eric W. Biederman
2020-03-02 16:43 ` Jann Horn
2020-03-02 17:01 ` Bernd Edlinger
2020-03-02 17:37 ` Jann Horn
2020-03-02 17:42 ` christian
2020-03-02 17:42 ` christian
2020-03-02 18:08 ` Jann Horn
2020-03-02 20:10 ` [PATCHv3] " Bernd Edlinger
2020-03-02 20:28 ` Bernd Edlinger
2020-03-03 20:13 ` [PATCHv2] " Eric W. Biederman
2020-03-02 17:13 ` Bernd Edlinger
2020-03-02 21:49 ` Eric W. Biederman
2020-03-02 22:00 ` Bernd Edlinger
2020-03-02 22:18 ` [PATCHv4] " Bernd Edlinger
2020-03-03 2:26 ` Kees Cook
2020-03-03 4:54 ` Bernd Edlinger
2020-03-03 5:29 ` Kees Cook
2020-03-03 8:08 ` Bernd Edlinger
2020-03-03 8:34 ` Christian Brauner
2020-03-03 8:43 ` Christian Brauner
2020-03-04 15:30 ` Christian Brauner
2020-03-03 8:58 ` Christian Brauner
2020-03-03 10:34 ` Bernd Edlinger
2020-03-03 11:23 ` Bernd Edlinger
2020-03-03 14:20 ` Christian Brauner
2020-03-03 13:02 ` [PATCHv5] " Bernd Edlinger
2020-03-03 15:18 ` Eric W. Biederman
2020-03-03 16:48 ` Bernd Edlinger
2020-03-03 17:01 ` Christian Brauner
2020-03-03 17:20 ` Christian Brauner
2020-03-03 20:08 ` Eric W. Biederman
2020-03-04 14:37 ` Bernd Edlinger
2020-03-04 16:33 ` Eric W. Biederman
2020-03-04 21:49 ` Bernd Edlinger
2020-03-04 21:56 ` [PATCHv6] " Bernd Edlinger
2020-03-05 18:36 ` Bernd Edlinger
2020-03-05 21:14 ` [PATCH 0/2] Infrastructure to allow fixing exec deadlocks Eric W. Biederman
2020-03-05 21:15 ` [PATCH 1/2] exec: Properly mark the point of no return Eric W. Biederman
2020-03-05 22:34 ` Bernd Edlinger
2020-03-06 5:19 ` Eric W. Biederman
2020-03-05 22:56 ` Bernd Edlinger
2020-03-06 5:09 ` Eric W. Biederman
2020-03-06 16:26 ` Bernd Edlinger
2020-03-06 17:16 ` Eric W. Biederman
2020-03-05 21:16 ` [PATCH 2/2] exec: Add a exec_update_mutex to replace cred_guard_mutex Eric W. Biederman
2020-03-05 21:51 ` Bernd Edlinger
2020-03-06 5:17 ` Eric W. Biederman
2020-03-06 11:46 ` Bernd Edlinger
2020-03-06 21:18 ` Eric W. Biederman
2020-03-06 19:16 ` Bernd Edlinger
2020-03-06 21:58 ` Eric W. Biederman
2020-03-06 22:29 ` Eric W. Biederman [this message]
2020-03-07 1:03 ` Eric W. Biederman
2020-03-08 12:58 ` [PATCH] exec: make de_thread alloc new signal struct earlier Bernd Edlinger
2020-03-08 18:12 ` Eric W. Biederman
2020-03-05 22:31 ` [PATCH 0/2] Infrastructure to allow fixing exec deadlocks Bernd Edlinger
2020-03-06 5:06 ` Eric W. Biederman
2020-03-08 21:34 ` [PATCH 0/5] " Eric W. Biederman
2020-03-08 21:35 ` [PATCH v2 1/5] exec: Only compute current once in flush_old_exec Eric W. Biederman
2020-03-09 13:56 ` Bernd Edlinger
2020-03-09 17:34 ` Eric W. Biederman
2020-03-09 17:56 ` Bernd Edlinger
2020-03-09 19:27 ` Bernd Edlinger
2020-03-10 20:17 ` Kees Cook
2020-03-10 21:12 ` Christian Brauner
2020-03-08 21:36 ` [PATCH v2 2/5] exec: Factor unshare_sighand out of de_thread and call it separately Eric W. Biederman
2020-03-09 19:28 ` Bernd Edlinger
2020-03-10 20:29 ` Kees Cook
2020-03-10 20:34 ` Bernd Edlinger
2020-03-10 20:57 ` Kees Cook
2020-03-10 21:21 ` Christian Brauner
2020-03-08 21:36 ` [PATCH v2 3/5] exec: Move cleanup of posix timers on exec out of de_thread Eric W. Biederman
2020-03-09 19:30 ` Bernd Edlinger
2020-03-09 19:59 ` Christian Brauner
2020-03-09 20:06 ` Eric W. Biederman
2020-03-09 20:17 ` Christian Brauner
2020-03-09 20:48 ` Eric W. Biederman
2020-03-10 8:55 ` Christian Brauner
2020-03-10 18:52 ` [PATCH] pidfd: Stop taking cred_guard_mutex Eric W. Biederman
2020-03-10 19:15 ` Christian Brauner
2020-03-10 19:16 ` Jann Horn
2020-03-10 19:27 ` Eric W. Biederman
2020-03-10 20:00 ` Jann Horn
2020-03-10 20:10 ` Jann Horn
2020-03-10 20:22 ` Bernd Edlinger
2020-03-11 6:11 ` Bernd Edlinger
2020-03-11 14:56 ` Jann Horn
2020-03-10 20:57 ` Eric W. Biederman
2020-03-10 21:29 ` Christian Brauner
2020-03-11 18:49 ` Kees Cook
2020-03-14 9:12 ` [PATCH] pidfd: Use new infrastructure to fix deadlocks in execve Bernd Edlinger
2020-03-10 20:16 ` [PATCH v2 3/5] exec: Move cleanup of posix timers on exec out of de_thread Kees Cook
2020-03-10 20:31 ` Kees Cook
2020-03-10 20:57 ` Jann Horn
2020-03-10 21:05 ` Eric W. Biederman
2020-03-10 21:22 ` Christian Brauner
2020-03-08 21:38 ` [PATCH v2 4/5] exec: Move exec_mmap right after de_thread in flush_old_exec Eric W. Biederman
2020-03-09 19:34 ` Bernd Edlinger
2020-03-09 19:45 ` Eric W. Biederman
2020-03-09 19:52 ` Bernd Edlinger
2020-03-09 19:58 ` Eric W. Biederman
2020-03-09 20:03 ` Bernd Edlinger
2020-03-09 20:35 ` Eric W. Biederman
2020-03-10 20:44 ` Kees Cook
2020-03-10 21:20 ` Eric W. Biederman
2020-03-10 20:47 ` Kees Cook
2020-03-10 21:09 ` Eric W. Biederman
2020-03-08 21:38 ` [PATCH v2 5/5] exec: Add a exec_update_mutex to replace cred_guard_mutex Eric W. Biederman
2020-03-09 13:45 ` Bernd Edlinger
2020-03-09 17:40 ` Eric W. Biederman
2020-03-09 18:01 ` Bernd Edlinger
2020-03-09 18:10 ` Eric W. Biederman
2020-03-09 18:24 ` Eric W. Biederman
2020-03-09 18:36 ` Eric W. Biederman
2020-03-09 18:47 ` Bernd Edlinger
2020-03-09 19:02 ` Eric W. Biederman
2020-03-09 19:24 ` Bernd Edlinger
2020-03-09 19:35 ` Eric W. Biederman
2020-03-09 19:39 ` Eric W. Biederman
2020-03-10 13:43 ` [PATCH 0/4] Use new infrastructure to fix deadlocks in execve Bernd Edlinger
2020-03-10 15:35 ` Eric W. Biederman
2020-03-10 17:44 ` [PATCH 0/4] Use new infrastructure in more simple cases Bernd Edlinger
2020-03-10 17:45 ` [PATCH 1/4] kernel/kcmp.c: Use new infrastructure to fix deadlocks in execve Bernd Edlinger
2020-03-10 19:01 ` Eric W. Biederman
2020-03-10 19:42 ` Bernd Edlinger
2020-03-10 17:45 ` [PATCH 2/4] proc: " Bernd Edlinger
2020-03-11 18:59 ` Kees Cook
2020-03-11 19:10 ` Kees Cook
2020-03-11 19:38 ` Bernd Edlinger
2020-03-10 17:45 ` [PATCH 3/4] proc: io_accounting: " Bernd Edlinger
2020-03-10 19:06 ` Eric W. Biederman
2020-03-10 20:19 ` Bernd Edlinger
2020-03-10 21:25 ` Eric W. Biederman
2020-03-11 19:08 ` Kees Cook
2020-03-11 19:48 ` Bernd Edlinger
2020-03-11 19:48 ` Eric W. Biederman
2020-03-10 17:45 ` [PATCH 4/4] perf: " Bernd Edlinger
2020-03-10 13:43 ` [PATCH 1/4] exec: Fix a deadlock in ptrace Bernd Edlinger
2020-03-10 15:13 ` Eric W. Biederman
2020-03-10 15:17 ` Bernd Edlinger
2020-03-10 21:00 ` Kees Cook
2020-03-10 13:44 ` [PATCH 2/4] selftests/ptrace: add test cases for dead-locks Bernd Edlinger
2020-03-10 21:36 ` Kees Cook
2020-03-10 22:41 ` Dmitry V. Levin
2020-03-10 13:44 ` [PATCH 3/4] mm: docs: Fix a comment in process_vm_rw_core Bernd Edlinger
2020-03-11 18:53 ` Kees Cook
2020-03-10 13:44 ` [PATCH 4/4] kernel: doc: remove outdated comment cred.c Bernd Edlinger
2020-03-11 18:54 ` Kees Cook
2020-03-09 19:33 ` [PATCH v2 5/5] exec: Add a exec_update_mutex to replace cred_guard_mutex Dmitry V. Levin
2020-03-09 19:42 ` Eric W. Biederman
2020-03-10 20:55 ` Kees Cook
2020-03-10 21:02 ` Eric W. Biederman
2020-03-10 21:21 ` Jann Horn
2020-03-10 21:30 ` Eric W. Biederman
2020-03-10 23:21 ` Jann Horn
2020-03-11 0:15 ` Eric W. Biederman
2020-03-11 6:33 ` Bernd Edlinger
2020-03-11 16:29 ` Eric W. Biederman
2020-03-11 13:18 ` Qian Cai
2020-03-12 10:27 ` Kirill Tkhai
2020-03-12 12:24 ` Eric W. Biederman
2020-03-12 13:45 ` Kirill Tkhai
2020-03-12 14:38 ` Eric W. Biederman
2020-03-12 15:23 ` Kirill Tkhai
2020-03-13 1:05 ` Bernd Edlinger
2020-03-13 9:13 ` Kirill Tkhai
2020-03-14 9:11 ` [PATCH v3 " Bernd Edlinger
2020-03-17 8:56 ` Kirill Tkhai
2020-03-17 21:53 ` Bernd Edlinger
2020-03-18 12:22 ` Kirill Tkhai
2020-03-18 20:06 ` Bernd Edlinger
2020-03-19 7:13 ` Kirill Tkhai
2020-03-19 7:19 ` Bernd Edlinger
2020-03-19 9:11 ` [PATCH v4 3/5] " Bernd Edlinger
2020-03-19 9:13 ` Bernd Edlinger
2020-03-19 9:19 ` Greg Kroah-Hartman
2020-03-19 9:20 ` Bernd Edlinger
2020-03-21 22:53 ` Bernd Edlinger
2020-03-14 9:12 ` [PATCH 0/2] exec: Fix dead-lock in de_thread with ptrace_attach Bernd Edlinger
2020-03-14 9:12 ` [PATCH 1/2] " Bernd Edlinger
2020-03-14 9:13 ` [PATCH 2/2] doc: Update documentation of ->exec_*_mutex Bernd Edlinger
2020-03-14 9:57 ` [PATCH v2 5/5] exec: Add a exec_update_mutex to replace cred_guard_mutex Bernd Edlinger
2020-03-14 10:02 ` Bernd Edlinger
2020-03-17 8:58 ` Kirill Tkhai
2020-03-09 13:58 ` [PATCH 0/5] Infrastructure to allow fixing exec deadlocks Bernd Edlinger
2020-03-03 16:50 ` [PATCHv5] exec: Fix a deadlock in ptrace Christian Brauner
2020-03-02 12:28 ` [PATCHv2] " Oleg Nesterov
2020-03-02 15:56 ` Bernd Edlinger
2020-03-02 7:47 ` [PATCH] " Christian Brauner
2020-03-02 7:48 ` Christian Brauner
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