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From: ebiederm@xmission.com (Eric W. Biederman)
To: Kees Cook <keescook@chromium.org>
Cc: Bernd Edlinger <bernd.edlinger@hotmail.de>,
	Christian Brauner <christian.brauner@ubuntu.com>,
	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 3/4] proc: io_accounting: Use new infrastructure to fix deadlocks in execve
Date: Wed, 11 Mar 2020 14:48:50 -0500
Message-ID: <87pndin04d.fsf@x220.int.ebiederm.org> (raw)
In-Reply-To: <202003111203.738487D@keescook> (Kees Cook's message of "Wed, 11 Mar 2020 12:08:08 -0700")

Kees Cook <keescook@chromium.org> writes:

> On Tue, Mar 10, 2020 at 06:45:47PM +0100, Bernd Edlinger wrote:
>> This changes do_io_accounting to use the new exec_update_mutex
>> instead of cred_guard_mutex.
>> 
>> This fixes possible deadlocks when the trace is accessing
>> /proc/$pid/io for instance.
>> 
>> This should be safe, as the credentials are only used for reading.
>
> I'd like to see the rationale described better here for why it should be
> safe. I'm still not seeing why this is safe here, as we might check
> ptrace_may_access() with one cred and then iterate io accounting with a
> different credential...
>
> What am I missing?

The rational for non-regression is that exec_update_mutex covers all
of the same tsk->cred changes as cred_guard_mutex.  Therefore we are not
any worse off, and we avoid the deadlock.

As for safety.  Jann's argument that the only interesting credential
change is in exec applies.  All other credential changes that have any
effect on permission checks make the new cred non-dumpable (excepions
apply see the code).

So I think this is a non-regressing change.  A safe change.

I don't think either version of this code is fully correct.

Eric

>> Signed-off-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
>> ---
>>  fs/proc/base.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>> 
>> diff --git a/fs/proc/base.c b/fs/proc/base.c
>> index 4fdfe4f..529d0c6 100644
>> --- a/fs/proc/base.c
>> +++ b/fs/proc/base.c
>> @@ -2770,7 +2770,7 @@ static int do_io_accounting(struct task_struct *task, struct seq_file *m, int wh
>>  	unsigned long flags;
>>  	int result;
>>  
>> -	result = mutex_lock_killable(&task->signal->cred_guard_mutex);
>> +	result = mutex_lock_killable(&task->signal->exec_update_mutex);
>>  	if (result)
>>  		return result;
>>  
>> @@ -2806,7 +2806,7 @@ static int do_io_accounting(struct task_struct *task, struct seq_file *m, int wh
>>  	result = 0;
>>  
>>  out_unlock:
>> -	mutex_unlock(&task->signal->cred_guard_mutex);
>> +	mutex_unlock(&task->signal->exec_update_mutex);
>>  	return result;
>>  }
>>  
>> -- 
>> 1.9.1

  parent reply index

Thread overview: 203+ 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 18:08                           ` Jann Horn
2020-03-02 20:10                             ` [PATCHv3] " Bernd Edlinger
2020-03-02 20:28                               ` Bernd Edlinger
2020-03-02 17:13                   ` [PATCHv2] " 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
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 [this message]
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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