Patchwork Yama: add PR_SET_PTRACER_ANY

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Submitter Kees Cook
Date Feb. 15, 2012, 9:34 p.m.
Message ID <20120215213454.GW20420@outflux.net>
Download mbox | patch
Permalink /patch/141412/
State New
Headers show

Comments

Kees Cook - Feb. 15, 2012, 9:34 p.m.
Hi guys,

I'd like to make sure this lands in Precise. Can someone pull this in?

Thanks!

-Kees

----- Forwarded message from Kees Cook <keescook@chromium.org> -----

Date: Tue, 14 Feb 2012 16:48:09 -0800
From: Kees Cook <keescook@chromium.org>
To: linux-security-module@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, John Johansen <john.johansen@canonical.com>,
	kernel-hardening@lists.openwall.com
Subject: [PATCH] Yama: add PR_SET_PTRACER_ANY

For a process to entirely disable Yama ptrace restrictions, it can use
the special PR_SET_PTRACER_ANY pid to indicate that any otherwise allowed
process may ptrace it. This is stronger than calling PR_SET_PTRACER with
pid "1" because it includes processes in external pid namespaces. This is
currently needed by the Chrome renderer, since its crash handler (Breakpad)
runs external to the renderer's pid namespace.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
 Documentation/security/Yama.txt |    7 ++++++-
 include/linux/prctl.h           |    1 +
 security/yama/yama_lsm.c        |    8 ++++++--
 3 files changed, 13 insertions(+), 3 deletions(-)
Tim Gardner - Feb. 16, 2012, 2:22 p.m.
On 02/15/2012 02:34 PM, Kees Cook wrote:
> Yama: add PR_SET_PTRACER_ANY

Kees - how about if I rebase all of the prior Yama commits out of 
existence, then pickup 'security: Yama LSM' and 'Yama: add 
PR_SET_PTRACER_ANY' from linux-next ?

rtg
Tim Gardner - Feb. 16, 2012, 2:54 p.m.
On 02/16/2012 07:22 AM, Tim Gardner wrote:
> On 02/15/2012 02:34 PM, Kees Cook wrote:
>> Yama: add PR_SET_PTRACER_ANY
>
> Kees - how about if I rebase all of the prior Yama commits out of
> existence, then pickup 'security: Yama LSM' and 'Yama: add
> PR_SET_PTRACER_ANY' from linux-next ?
>
> rtg

Couldn't wait, did it anyways. You gotta start work earlier :)

I checked that Yama has shuddered to life, so I assume its doing what it 
was designed to do:

Feb 16 07:47:34 mba kernel: [    0.000051] Yama: becoming mindful.

rtg
Kees Cook - Feb. 16, 2012, 4:22 p.m.
On Thu, Feb 16, 2012 at 07:22:16AM -0700, Tim Gardner wrote:
> On 02/15/2012 02:34 PM, Kees Cook wrote:
> >Yama: add PR_SET_PTRACER_ANY
> 
> Kees - how about if I rebase all of the prior Yama commits out of
> existence, then pickup 'security: Yama LSM' and 'Yama: add
> PR_SET_PTRACER_ANY' from linux-next ?

That should be fine as long as the "unconditionally chain to Yama" patch
stays in (which isn't and won't be upstream).

Thanks!

-Kees
Kees Cook - Feb. 16, 2012, 4:31 p.m.
On Thu, Feb 16, 2012 at 08:22:28AM -0800, Kees Cook wrote:
> On Thu, Feb 16, 2012 at 07:22:16AM -0700, Tim Gardner wrote:
> > On 02/15/2012 02:34 PM, Kees Cook wrote:
> > >Yama: add PR_SET_PTRACER_ANY
> > 
> > Kees - how about if I rebase all of the prior Yama commits out of
> > existence, then pickup 'security: Yama LSM' and 'Yama: add
> > PR_SET_PTRACER_ANY' from linux-next ?
> 
> That should be fine as long as the "unconditionally chain to Yama" patch
> stays in (which isn't and won't be upstream).

Agh, no, what am I saying? This won't work because upstream doesn't have
the link restrictions. Please pull from here, if you want as close a view
to upstream as possible:

http://git.kernel.org/?p=linux/kernel/git/kees/linux.git;a=shortlog;h=refs/heads/yama

-Kees
John Johansen - Feb. 16, 2012, 5:34 p.m.
On 02/16/2012 08:31 AM, Kees Cook wrote:
> On Thu, Feb 16, 2012 at 08:22:28AM -0800, Kees Cook wrote:
>> On Thu, Feb 16, 2012 at 07:22:16AM -0700, Tim Gardner wrote:
>>> On 02/15/2012 02:34 PM, Kees Cook wrote:
>>>> Yama: add PR_SET_PTRACER_ANY
>>>
>>> Kees - how about if I rebase all of the prior Yama commits out of
>>> existence, then pickup 'security: Yama LSM' and 'Yama: add
>>> PR_SET_PTRACER_ANY' from linux-next ?
>>
>> That should be fine as long as the "unconditionally chain to Yama" patch
>> stays in (which isn't and won't be upstream).
> 
> Agh, no, what am I saying? This won't work because upstream doesn't have
> the link restrictions. Please pull from here, if you want as close a view
> to upstream as possible:
> 
yeah that + the lack of stacking/chaining is a real problem for the upstream
version atm

> http://git.kernel.org/?p=linux/kernel/git/kees/linux.git;a=shortlog;h=refs/heads/yama
> 
this looks good

Acked-by: John Johansen <john.johansen@canonical.com>

Patch

diff --git a/Documentation/security/Yama.txt b/Documentation/security/Yama.txt
index 4f0b789..a9511f1 100644
--- a/Documentation/security/Yama.txt
+++ b/Documentation/security/Yama.txt
@@ -41,7 +41,12 @@  other process (and its descendents) are allowed to call PTRACE_ATTACH
 against it. Only one such declared debugging process can exists for
 each inferior at a time. For example, this is used by KDE, Chromium, and
 Firefox's crash handlers, and by Wine for allowing only Wine processes
-to ptrace each other.
+to ptrace each other. If a process wishes to entirely disable these ptrace
+restrictions, it can call prctl(PR_SET_PTRACER, PR_SET_PTRACER_ANY, ...)
+so that any otherwise allowed process (even those in external pid namespaces)
+may attach.
+
+The sysctl settings are:
 
 0 - classic ptrace permissions: a process can PTRACE_ATTACH to any other
     process running under the same uid, as long as it is dumpable (i.e.
diff --git a/include/linux/prctl.h b/include/linux/prctl.h
index 4d0e5bc..a0413ac 100644
--- a/include/linux/prctl.h
+++ b/include/linux/prctl.h
@@ -119,5 +119,6 @@ 
  * A value of 0 mean "no process".
  */
 #define PR_SET_PTRACER 0x59616d61
+# define PR_SET_PTRACER_ANY ((unsigned long)-1)
 
 #endif /* _LINUX_PRCTL_H */
diff --git a/security/yama/yama_lsm.c b/security/yama/yama_lsm.c
index dd4d360..5737238 100644
--- a/security/yama/yama_lsm.c
+++ b/security/yama/yama_lsm.c
@@ -84,7 +84,7 @@  static void yama_ptracer_del(struct task_struct *tracer,
 	spin_lock_bh(&ptracer_relations_lock);
 	list_for_each_entry_safe(relation, safe, &ptracer_relations, node)
 		if (relation->tracee == tracee ||
-		    relation->tracer == tracer) {
+		    (tracer && relation->tracer == tracer)) {
 			list_del(&relation->node);
 			kfree(relation);
 		}
@@ -138,6 +138,8 @@  static int yama_task_prctl(int option, unsigned long arg2, unsigned long arg3,
 		if (arg2 == 0) {
 			yama_ptracer_del(NULL, myself);
 			rc = 0;
+		} else if (arg2 == PR_SET_PTRACER_ANY) {
+			rc = yama_ptracer_add(NULL, myself);
 		} else {
 			struct task_struct *tracer;
 
@@ -208,6 +210,7 @@  static int ptracer_exception_found(struct task_struct *tracer,
 	int rc = 0;
 	struct ptrace_relation *relation;
 	struct task_struct *parent = NULL;
+	bool found = false;
 
 	spin_lock_bh(&ptracer_relations_lock);
 	rcu_read_lock();
@@ -216,10 +219,11 @@  static int ptracer_exception_found(struct task_struct *tracer,
 	list_for_each_entry(relation, &ptracer_relations, node)
 		if (relation->tracee == tracee) {
 			parent = relation->tracer;
+			found = true;
 			break;
 		}
 
-	if (task_is_descendant(parent, tracer))
+	if (found && (parent == NULL || task_is_descendant(parent, tracer)))
 		rc = 1;
 	rcu_read_unlock();
 	spin_unlock_bh(&ptracer_relations_lock);