Re: [PATCH] psi: allow unprivileged users with CAP_SYS_RESOURCE to write psi files

Peter Zijlstra
2021-04-01T06:48:25Z

On Wed, Mar 31, 2021 at 11:31:56PM -0400, Josh Hunt wrote:
> Currently only root can write files under /proc/pressure. Relax this to
> allow tasks running as unprivileged users with CAP_SYS_RESOURCE to be
> able to write to these files.
>
> Signed-off-by: Josh Hunt <johunt@akamai.com>

I suppose that's ok, but lets also ask Johannes.

> ---
> kernel/sched/psi.c | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
> index b1b00e9bd7ed..98ff7baf1ba8 100644
> --- a/kernel/sched/psi.c
> +++ b/kernel/sched/psi.c
> @@ -1270,6 +1270,9 @@ static ssize_t psi_write(struct file *file, const char __user *user_buf,
> if (!nbytes)
> return -EINVAL;
>
> + if (!capable(CAP_SYS_RESOURCE))
> + return -EPERM;
> +
> buf_size = min(nbytes, sizeof(buf));
> if (copy_from_user(buf, user_buf, buf_size))
> return -EFAULT;
> @@ -1353,9 +1356,9 @@ static int __init psi_proc_init(void)
> {
> if (psi_enable) {
> proc_mkdir("pressure", NULL);
> - proc_create("pressure/io", 0, NULL, &psi_io_proc_ops);
> - proc_create("pressure/memory", 0, NULL, &psi_memory_proc_ops);
> - proc_create("pressure/cpu", 0, NULL, &psi_cpu_proc_ops);
> + proc_create("pressure/io", 0666, NULL, &psi_io_proc_ops);
> + proc_create("pressure/memory", 0666, NULL, &psi_memory_proc_ops);
> + proc_create("pressure/cpu", 0666, NULL, &psi_cpu_proc_ops);
> }
> return 0;
> }
> --
> 2.17.1
>