[PATCH v2] proc: use ns_capable instead of capable for timerslack_ns

From: Benjamin Gordon
Date: Tue Oct 30 2018 - 14:00:38 EST

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@xxxxxxxxxx>
Cc: John Stultz <john.stultz@xxxxxxxxxx>
Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: "Serge E. Hallyn" <serge@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
Cc: Oren Laadan <orenl@xxxxxxxxxxx>
Cc: Ruchi Kandoi <kandoiruchi@xxxxxxxxxx>
Cc: Rom Lemarchand <romlem@xxxxxxxxxxx>
Cc: Todd Kjos <tkjos@xxxxxxxxxx>
Cc: Colin Cross <ccross@xxxxxxxxxxx>
Cc: Nick Kralevich <nnk@xxxxxxxxxx>
Cc: Dmitry Shmidt <dimitrysh@xxxxxxxxxx>
Cc: Elliott Hughes <enh@xxxxxxxxxx>
Cc: Android Kernel Team <kernel-team@xxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>

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

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;