bmgor...@google.com writes:
> From: Benjamin Gordon <bmgor...@google.com>
>
> 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.
The goal seems legitimate. However the permission checks look wrong.
In particular the choice of user namespace should be
"p->cred->user_ns". This will limit this to tasks that have
CAP_SYS_NICE in the same namespace as the task that is being modified.
Testing file->f_cred->user_ns it is testing whoever opened the file and
that could be anyone.
Eric
> Signed-off-by: Benjamin Gordon <bmgor...@google.com>
> Cc: John Stultz <john.stu...@linaro.org>
> 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>
> ---
> fs/proc/base.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 7e9f07bf260d..4b50937dff80 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -2356,7 +2356,7 @@ static ssize_t timerslack_ns_write(struct file *file,
> const char __user *buf,
> return -ESRCH;
>
> if (p != current) {
> - if (!capable(CAP_SYS_NICE)) {
> + if (!ns_capable(file->f_cred->user_ns, CAP_SYS_NICE)) {
> count = -EPERM;
> goto out;
> }
> @@ -2393,7 +2393,7 @@ static int timerslack_ns_show(struct seq_file *m, void
> *v)
>
> if (p != current) {
>
> - if (!capable(CAP_SYS_NICE)) {
> + if (!ns_capable(seq_user_ns(m), CAP_SYS_NICE)) {
> err = -EPERM;
> goto out;
> }
