fs/proc/base.c: 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.

Link: http://lkml.kernel.org/r/20181030180012.232896-1-bmgordon@google.com
Signed-off-by: Benjamin Gordon <bmgordon@google.com>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: "Serge E. Hallyn" <serge@hallyn.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Oren Laadan <orenl@cellrox.com>
Cc: Ruchi Kandoi <kandoiruchi@google.com>
Cc: Rom Lemarchand <romlem@android.com>
Cc: Todd Kjos <tkjos@google.com>
Cc: Colin Cross <ccross@android.com>
Cc: Nick Kralevich <nnk@google.com>
Cc: Dmitry Shmidt <dimitrysh@google.com>
Cc: Elliott Hughes <enh@google.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/proc/base.c b/fs/proc/base.c
index d7fd1ca..58a8dc3 100644 (file)
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2356,10 +2356,13 @@ 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) {
@@ -2392,11 +2395,14 @@ 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;