From: Jann Horn <jann@thejh.net>
To: Stephen Smalley <sds@tycho.nsa.gov>
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>,
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 3/9] proc: use open()-time creds for ptrace checks
Date: Mon, 19 Sep 2016 16:32:07 +0200 [thread overview]
Message-ID: <20160919143206.GC2903@pc.thejh.net> (raw)
In-Reply-To: <4f10ddba-fb7c-04a3-0426-550b435e6f3a@tycho.nsa.gov>
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On Mon, Sep 19, 2016 at 09:01:19AM -0400, Stephen Smalley wrote:
> On 09/18/2016 11:05 AM, Jann Horn wrote:
> > This adds a new ptrace_may_access_noncurrent() method that
> > uses the supplied credentials instead of those of the
> > current task. (However, the current task may still be
> > inspected for auditing purposes, e.g. by the Smack LSM.)
> >
> > procfs used the caller's creds for a few ptrace_may_access()
> > checks at read() time, which made a confused deputy attack
> > by passing an FD to a procfs file to a setuid program
> > possible. Therefore, the following was a local userspace
> > ASLR bypass:
[...]
> > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> > index 13185a6..f9a0be7 100644
> > --- a/security/selinux/hooks.c
> > +++ b/security/selinux/hooks.c
> > @@ -2133,10 +2133,10 @@ static int selinux_binder_transfer_file(struct task_struct *from,
> > }
> >
> > static int selinux_ptrace_access_check(struct task_struct *child,
> > - unsigned int mode)
> > + unsigned int mode, const struct cred *cred)
> > {
> > if (mode & PTRACE_MODE_READ) {
> > - u32 sid = current_sid();
> > + u32 sid = cred_sid(cred);
> > u32 csid = task_sid(child);
> > return avc_has_perm(sid, csid, SECCLASS_FILE, FILE__READ, NULL);
> > }
>
> For consistency, don't you also need to change the next line of code to
> use cred_has_perm() rather than current_has_perm()?
Oh, right.
How about something like this?
u32 sid = cred_sid(cred);
u32 csid = task_sid(child);
if (mode & PTRACE_MODE_READ)
return avc_has_perm(sid, csid, SECCLASS_FILE, FILE__READ, NULL);
else
return avc_has_perm(sid, csid, SECCLASS_PROCESS, PROCESS__PTRACE, NULL);
The current code looks as if the PTRACE_MODE_READ and PTRACE_MODE_ATTACH cases
behave very differently, which they actually don't. And to be able to use
cred_has_perm() here, it would be necessary to explicitly grab and release
an RCU read lock or so (to prevent the child creds from going away).
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next prev parent reply other threads:[~2016-09-19 14:32 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 [this message]
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
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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