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Message-ID: <202003111159.5D5B240F@keescook>
Date: Wed, 11 Mar 2020 11:59:38 -0700
From: Kees Cook <keescook@...omium.org>
To: Bernd Edlinger <bernd.edlinger@...mail.de>
Cc: "Eric W. Biederman" <ebiederm@...ssion.com>,
Christian Brauner <christian.brauner@...ntu.com>,
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" <linux-api@...r.kernel.org>
Subject: Re: [PATCH 2/4] proc: Use new infrastructure to fix deadlocks in
execve
On Tue, Mar 10, 2020 at 06:45:32PM +0100, Bernd Edlinger wrote:
> This changes lock_trace to use the new exec_update_mutex
> instead of cred_guard_mutex.
>
> This fixes possible deadlocks when the trace is accessing
> /proc/$pid/stack for instance.
>
> This should be safe, as the credentials are only used for reading,
> and task->mm is updated on execve under the new exec_update_mutex.
>
> Signed-off-by: Bernd Edlinger <bernd.edlinger@...mail.de>
Reviewed-by: Kees Cook <keescook@...omium.org>
-Kees
> ---
> fs/proc/base.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index ebea950..4fdfe4f 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -403,11 +403,11 @@ static int proc_pid_wchan(struct seq_file *m, struct pid_namespace *ns,
>
> static int lock_trace(struct task_struct *task)
> {
> - int err = mutex_lock_killable(&task->signal->cred_guard_mutex);
> + int err = mutex_lock_killable(&task->signal->exec_update_mutex);
> if (err)
> return err;
> if (!ptrace_may_access(task, PTRACE_MODE_ATTACH_FSCREDS)) {
> - mutex_unlock(&task->signal->cred_guard_mutex);
> + mutex_unlock(&task->signal->exec_update_mutex);
> return -EPERM;
> }
> return 0;
> @@ -415,7 +415,7 @@ static int lock_trace(struct task_struct *task)
>
> static void unlock_trace(struct task_struct *task)
> {
> - mutex_unlock(&task->signal->cred_guard_mutex);
> + mutex_unlock(&task->signal->exec_update_mutex);
> }
>
> #ifdef CONFIG_STACKTRACE
> --
> 1.9.1
--
Kees Cook
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