Benjamin Gordon <bmgor...@google.com> writes: > 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.
Acked-by: "Eric W. Biederman" <ebied...@xmission.com> I don't see any fundamental probess with how the processes user namespace is being accessed. You can race with setns and that may result in a descendent user namespace of the current user namespace being set. But if you have permissions in the parent user namespace you will have permissions over a child user namespace. So the race can't effect the outcome of the ns_capable test. That and while __task_cred(p) may change it is guaranteed there is a valid one until __put_task_struct which only happens when a process has a zero refcount. Which the success of get_proc_task in before these checks already ensures is not true. So from my perspective this looks like a reasonable change. I don't know how this looks from people who understand the timer bits and what timerslack does. I suspect it is reasonable as there is no permission check for changing yourself. Eric > Signed-off-by: Benjamin Gordon <bmgor...@google.com> > Cc: John Stultz <john.stu...@linaro.org> > Cc: "Eric W. Biederman" <ebied...@xmission.com> > Cc: Kees Cook <keesc...@chromium.org> > Cc: "Serge E. Hallyn" <se...@hallyn.com> > Cc: Thomas Gleixner <t...@linutronix.de> > Cc: Arjan van de Ven <ar...@linux.intel.com> > Cc: Oren Laadan <or...@cellrox.com> > Cc: Ruchi Kandoi <kandoiru...@google.com> > Cc: Rom Lemarchand <rom...@android.com> > Cc: Todd Kjos <tk...@google.com> > Cc: Colin Cross <ccr...@android.com> > Cc: Nick Kralevich <n...@google.com> > Cc: Dmitry Shmidt <dimitr...@google.com> > Cc: Elliott Hughes <e...@google.com> > Cc: Android Kernel Team <kernel-t...@android.com> > Cc: Andrew Morton <a...@linux-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;