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From: Linus Torvalds <torvalds@linux-foundation.org>
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 <linux-fsdevel@vger.kernel.org>,
	LSM List <linux-security-module@vger.kernel.org>,
	"security@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 13:18:48 -0700	[thread overview]
Message-ID: <CA+55aFwWSWJc17cpNUqWUUahp81zomSpOamDmF_JhYTRZoLecA@mail.gmail.com> (raw)
In-Reply-To: <1474211117-16674-8-git-send-email-jann@thejh.net>

On Sun, Sep 18, 2016 at 8:05 AM, Jann Horn <jann@thejh.net> 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.

Quite frankly, this smells like it should be a static check, not some
kind of runtime one. Or if runtime, it should be abstracted out so
that you can do an occasional "let's run a checking pass" rather than
enable it unconditionally and universally.

It's just too specialized. Soon you'll want to do other random context
checking, and we can't just keep adding those kinds of ad-hoc things
without it becoming a maintenance nightmare. I can well imagine
somebody ending up writing some stupid patch to take that
"in_unprivileged_vfs" thing into account for some semantics, and then
we're *really* screwed. So there are many reasons to make sure this is
*not* something that people actually expect to always be there.

               Linus

  parent reply	other threads:[~2016-09-18 20:18 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
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 [this message]
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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