linux-kernel - [PATCH v2] proc: use ns_capable instead of capable for timerslack

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Message-Id: <20181030180012.232896-1-bmgordon@google.com>
Date:   Tue, 30 Oct 2018 12:00:12 -0600
From:   Benjamin Gordon <bmgordon@...gle.com>
To:     linux-kernel@...r.kernel.org
Cc:     Benjamin Gordon <bmgordon@...gle.com>,
        John Stultz <john.stultz@...aro.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Kees Cook <keescook@...omium.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Oren Laadan <orenl@...lrox.com>,
        Ruchi Kandoi <kandoiruchi@...gle.com>,
        Rom Lemarchand <romlem@...roid.com>,
        Todd Kjos <tkjos@...gle.com>, Colin Cross <ccross@...roid.com>,
        Nick Kralevich <nnk@...gle.com>,
        Dmitry Shmidt <dimitrysh@...gle.com>,
        Elliott Hughes <enh@...gle.com>,
        Android Kernel Team <kernel-team@...roid.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH v2] proc: use ns_capable instead of capable for timerslack_ns

Access to timerslack_ns is controlled by a process having CAP_SYS_NICE
in its effective capability set, but the current check looks in the root
namespace instead of the process' user namespace.  Since a process is
allowed to do other activities controlled by CAP_SYS_NICE inside a
namespace, it should also be able to adjust timerslack_ns.

Signed-off-by: Benjamin Gordon <bmgordon@...gle.com>
Cc: John Stultz <john.stultz@...aro.org>
Cc: "Eric W. Biederman" <ebiederm@...ssion.com>
Cc: Kees Cook <keescook@...omium.org>
Cc: "Serge E. Hallyn" <serge@...lyn.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Arjan van de Ven <arjan@...ux.intel.com>
Cc: Oren Laadan <orenl@...lrox.com>
Cc: Ruchi Kandoi <kandoiruchi@...gle.com>
Cc: Rom Lemarchand <romlem@...roid.com>
Cc: Todd Kjos <tkjos@...gle.com>
Cc: Colin Cross <ccross@...roid.com>
Cc: Nick Kralevich <nnk@...gle.com>
Cc: Dmitry Shmidt <dimitrysh@...gle.com>
Cc: Elliott Hughes <enh@...gle.com>
Cc: Android Kernel Team <kernel-team@...roid.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
---

Changes from v1:
  - Use the namespace of the target process instead of the file opener.
    Didn't carry over John Stultz' Acked-by since the changes aren't
    cosmetic.

 fs/proc/base.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index c78d8da09b52c..bdc093ba81dd3 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2385,10 +2385,13 @@ static ssize_t timerslack_ns_write(struct file *file, const char __user *buf,
 		return -ESRCH;
 
 	if (p != current) {
-		if (!capable(CAP_SYS_NICE)) {
+		rcu_read_lock();
+		if (!ns_capable(__task_cred(p)->user_ns, CAP_SYS_NICE)) {
+			rcu_read_unlock();
 			count = -EPERM;
 			goto out;
 		}
+		rcu_read_unlock();
 
 		err = security_task_setscheduler(p);
 		if (err) {
@@ -2421,11 +2424,14 @@ static int timerslack_ns_show(struct seq_file *m, void *v)
 		return -ESRCH;
 
 	if (p != current) {
-
-		if (!capable(CAP_SYS_NICE)) {
+		rcu_read_lock();
+		if (!ns_capable(__task_cred(p)->user_ns, CAP_SYS_NICE)) {
+			rcu_read_unlock();
 			err = -EPERM;
 			goto out;
 		}
+		rcu_read_unlock();
+
 		err = security_task_getscheduler(p);
 		if (err)
 			goto out;
-- 
2.19.1.568.g152ad8e336-goog