On Fri, Jan 08, 2021 at 12:58:57PM -0800, Suren Baghdasaryan wrote:
> process_madvise currently requires ptrace attach capability.
> PTRACE_MODE_ATTACH gives one process complete control over another
> process. It effectively removes the security boundary between the
> two processes (in one direction). Granting ptrace attach capability
> even to a system process is considered dangerous since it creates an
> attack surface. This severely limits the usage of this API.
> The operations process_madvise can perform do not affect the correctness
> of the operation of the target process; they only affect where the data
> is physically located (and therefore, how fast it can be accessed).
> What we want is the ability for one process to influence another process
> in order to optimize performance across the entire system while leaving
> the security boundary intact.
> Replace PTRACE_MODE_ATTACH with a combination of PTRACE_MODE_READ
> and CAP_SYS_NICE. PTRACE_MODE_READ to prevent leaking ASLR metadata
> and CAP_SYS_NICE for influencing process performance.
>
> Signed-off-by: Suren Baghdasaryan <sur...@google.com>
It sounds logical to me.
If security folks don't see any concern and fix below,
Acked-by: Minchan Kim <minc...@kernel.org>
> @@ -1197,12 +1197,22 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const
> struct iovec __user *, vec,
> goto release_task;
> }
>
> - mm = mm_access(task, PTRACE_MODE_ATTACH_FSCREDS);
> + /* Require PTRACE_MODE_READ to avoid leaking ASLR metadata. */
> + mm = mm_access(task, PTRACE_MODE_READ_FSCREDS);
> if (IS_ERR_OR_NULL(mm)) {
> ret = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH;
> goto release_task;
> }
>
> + /*
> + * Require CAP_SYS_NICE for influencing process performance. Note that
> + * only non-destructive hints are currently supported.
> + */
> + if (!capable(CAP_SYS_NICE)) {
> + ret = -EPERM;
> + goto release_task;
mmput?
> + }
> +
> total_len = iov_iter_count(&iter);
>
> while (iov_iter_count(&iter)) {
> --
> 2.30.0.284.gd98b1dd5eaa7-goog
>
