[PATCH RFC v2 5/6] proc: instantiate only pids that we can ptrace on 'limit_pids=1' mount option

[Andy Lutomirski]

On Tue, Apr 25, 2017 at 5:23 AM, Djalal Harouni <tixxdz at gmail.com> wrote:
> If "limit_pids=1" mount option is set then do not instantiate pids that
> we can not ptrace. "limit_pids=1" means that procfs should only contain
> pids that the caller can ptrace.
>
> Cc: Kees Cook <keescook at chromium.org>
> Cc: Andy Lutomirski <luto at kernel.org>
> Signed-off-by: Djalal Harouni <tixxdz at gmail.com>
> ---
>  fs/proc/base.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 2e0f661..a663284 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -3149,6 +3149,7 @@ struct dentry *proc_pid_lookup(struct inode *dir, struct dentry * dentry, unsign
>         unsigned tgid;
>         struct proc_fs_info *fs_info = proc_sb(dir->i_sb);
>         struct pid_namespace *ns = fs_info->pid_ns;
> +       int limit_pids = proc_fs_limit_pids(fs_info);

Shouldn't the addition of proc_fs_limit_pids() be in this patch?

Also, can we name it something self-documented?
"ptraceable_pids_only=1", perhaps?  Or even pids=ptraceable (as
opposed to pids=all or maybe other choices in the future)?

--Andy
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