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From: Ben Hutchings <ben@decadent.org.uk>
To: Jann Horn <jann@thejh.net>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
	Roland McGrath <roland@hack.frob.com>,
	Oleg Nesterov <oleg@redhat.com>,
	John Johansen <john.johansen@canonical.com>,
	James Morris <james.l.morris@oracle.com>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	Paul Moore <aul@paul-moore.com>,
	Stephen Smalley <sds@tycho.nsa.gov>,
	Eric Paris <eparis@parisplace.org>,
	Casey Schaufler <casey@schaufler-ca.com>,
	Kees Cook <eescook@chromium.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Janis Danisevskis <jdanis@google.com>,
	Seth Forshee <seth.forshee@canonical.com>,
	"Eric . Biederman" <ebiederm@xmission.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Benjamin LaHaise <bcrl@kvack.org>,
	linux-fsdevel@vger.kernel.org,
	linux-security-module@vger.kernel.org, security@kernel.org
Subject: Re: [PATCH 7/9] ptrace: forbid ptrace checks against current_cred() from VFS context
Date: Sun, 18 Sep 2016 19:38:48 +0100	[thread overview]
Message-ID: <20160918183848.GS10601@decadent.org.uk> (raw)
In-Reply-To: <1474211117-16674-8-git-send-email-jann@thejh.net>

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On Sun, Sep 18, 2016 at 05:05:15PM +0200, Jann Horn wrote:
> This ensures that VFS implementations don't call ptrace_may_access() from
> VFS read or write handlers. In order for file descriptor passing to have
> its intended security properties, VFS read/write handlers must not do any
> kind of privilege checking.
[...]
> --- a/kernel/ptrace.c
> +++ b/kernel/ptrace.c
> @@ -302,6 +302,13 @@ ok:
>  bool ptrace_may_access(struct task_struct *task, unsigned int mode)
>  {
>  	int err;
> +
> +	/* If you have to check for ptrace access from a VFS method, use
> +	 * ptrace_may_access_noncurrent() instead.
> +	 */
> +	if (WARN_ON(current->in_unprivileged_vfs != 0))

Shouldn't this be WARN_ON_ONCE(), so that any such bug can't e used
to spam the log?

Ben.

> +		return false;
> +
>  	task_lock(task);
>  	err = __ptrace_may_access(task, mode, current_cred(),
>  				  &current->self_privunit_id);

-- 
Ben Hutchings
Reality is just a crutch for people who can't handle science fiction.

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  reply	other threads:[~2016-09-18 18:39 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-09-18 15:05 [PATCH 0/9] Various fixes related to ptrace_may_access() Jann Horn
2016-09-18 15:05 ` [PATCH 1/9] exec: introduce cred_guard_light Jann Horn
2016-09-18 15:05 ` [PATCH 2/9] exec: turn self_exec_id into self_privunit_id Jann Horn
2016-09-18 18:13   ` Ben Hutchings
2016-09-18 18:31     ` Jann Horn
2016-09-18 18:45       ` Ben Hutchings
2016-09-18 19:08         ` Jann Horn
2016-09-18 19:57         ` Andy Lutomirski
2016-09-19 15:31           ` Jann Horn
2016-09-18 15:05 ` [PATCH 3/9] proc: use open()-time creds for ptrace checks Jann Horn
2016-09-19 13:01   ` Stephen Smalley
2016-09-19 14:32     ` Jann Horn
2016-09-19 14:45       ` Stephen Smalley
2016-09-18 15:05 ` [PATCH 4/9] futex: don't leak robust_list pointer Jann Horn
2016-09-18 18:28   ` Ben Hutchings
2016-09-18 18:33     ` Jann Horn
2016-09-18 15:05 ` [PATCH 5/9] proc: lock properly in ptrace_may_access callers Jann Horn
2016-09-18 19:15   ` Jann Horn
2016-09-18 15:05 ` [PATCH 6/9] ptrace: warn on ptrace_may_access without proper locking Jann Horn
2016-09-18 15:05 ` [PATCH 7/9] ptrace: forbid ptrace checks against current_cred() from VFS context Jann Horn
2016-09-18 18:38   ` Ben Hutchings [this message]
2016-09-18 18:40     ` Jann Horn
2016-09-18 19:57   ` Andy Lutomirski
2016-09-18 20:38     ` Jann Horn
2016-09-18 20:18   ` Linus Torvalds
2016-09-18 20:52     ` Jann Horn
2016-09-18 15:05 ` [PATCH 8/9] fs/proc: fix attr access check Jann Horn
2016-09-18 15:05 ` [PATCH 9/9] Documentation: add security/ptrace_checks.txt Jann Horn

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