linux-kernel - Re: [PATCH 1/2] procfs: use an enum for possible hidepid values

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Date:   Thu, 3 Nov 2016 09:49:49 -0600
From:   Kees Cook <keescook@...omium.org>
To:     Lafcadio Wluiki <wluikil@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] procfs: use an enum for possible hidepid values

On Thu, Nov 3, 2016 at 9:30 AM, Lafcadio Wluiki <wluikil@...il.com> wrote:
> (Third, rebased submission, since first two submissions yielded no replies.)

Hm, I didn't see this series before, for some reason.

> Previously, the hidepid parameter was checked by comparing literal
> integers 0, 1, 2. Let's add a proper enum for this, to make the checking
> more expressive:
>
>         0 → HIDEPID_OFF
>         1 → HIDEPID_NO_ACCESS
>         2 → HIDEPID_INVISIBLE
>
> This changes the internal labelling only, the userspace-facing interface
> remains unmodified, and still works with literal integers 0, 1, 2.
>
> No functional changes.
>
> Signed-off-by: Lafcadio Wluiki <wluikil@...il.com>

Yup, this is good. Dropping literals is always preferred. :)

Acked-by: Kees Cook <keescook@...omium.org>

-Kees

> ---
>  fs/proc/base.c                | 8 ++++----
>  fs/proc/inode.c               | 2 +-
>  fs/proc/root.c                | 3 ++-
>  include/linux/pid_namespace.h | 6 ++++++
>  4 files changed, 13 insertions(+), 6 deletions(-)
>
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index ca651ac..ae5e13c 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -726,11 +726,11 @@ static int proc_pid_permission(struct inode *inode, int mask)
>         task = get_proc_task(inode);
>         if (!task)
>                 return -ESRCH;
> -       has_perms = has_pid_permissions(pid, task, 1);
> +       has_perms = has_pid_permissions(pid, task, HIDEPID_NO_ACCESS);
>         put_task_struct(task);
>
>         if (!has_perms) {
> -               if (pid->hide_pid == 2) {
> +               if (pid->hide_pid == HIDEPID_INVISIBLE) {
>                         /*
>                          * Let's make getdents(), stat(), and open()
>                          * consistent with each other.  If a process
> @@ -1720,7 +1720,7 @@ int pid_getattr(struct vfsmount *mnt, struct dentry *dentry, struct kstat *stat)
>         stat->gid = GLOBAL_ROOT_GID;
>         task = pid_task(proc_pid(inode), PIDTYPE_PID);
>         if (task) {
> -               if (!has_pid_permissions(pid, task, 2)) {
> +               if (!has_pid_permissions(pid, task, HIDEPID_INVISIBLE)) {
>                         rcu_read_unlock();
>                         /*
>                          * This doesn't prevent learning whether PID exists,
> @@ -3181,7 +3181,7 @@ int proc_pid_readdir(struct file *file, struct dir_context *ctx)
>              iter.tgid += 1, iter = next_tgid(ns, iter)) {
>                 char name[PROC_NUMBUF];
>                 int len;
> -               if (!has_pid_permissions(ns, iter.task, 2))
> +               if (!has_pid_permissions(ns, iter.task, HIDEPID_INVISIBLE))
>                         continue;
>
>                 len = snprintf(name, sizeof(name), "%d", iter.tgid);
> diff --git a/fs/proc/inode.c b/fs/proc/inode.c
> index e69ebe6..872325e 100644
> --- a/fs/proc/inode.c
> +++ b/fs/proc/inode.c
> @@ -106,7 +106,7 @@ static int proc_show_options(struct seq_file *seq, struct dentry *root)
>
>         if (!gid_eq(pid->pid_gid, GLOBAL_ROOT_GID))
>                 seq_printf(seq, ",gid=%u", from_kgid_munged(&init_user_ns, pid->pid_gid));
> -       if (pid->hide_pid != 0)
> +       if (pid->hide_pid != HIDEPID_OFF)
>                 seq_printf(seq, ",hidepid=%u", pid->hide_pid);
>
>         return 0;
> diff --git a/fs/proc/root.c b/fs/proc/root.c
> index 8d3e484..2989731 100644
> --- a/fs/proc/root.c
> +++ b/fs/proc/root.c
> @@ -58,7 +58,8 @@ int proc_parse_options(char *options, struct pid_namespace *pid)
>                 case Opt_hidepid:
>                         if (match_int(&args[0], &option))
>                                 return 0;
> -                       if (option < 0 || option > 2) {
> +                       if (option < HIDEPID_OFF ||
> +                           option > HIDEPID_INVISIBLE) {
>                                 pr_err("proc: hidepid value must be between 0 and 2.\n");
>                                 return 0;
>                         }
> diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
> index 34cce96..c2a989d 100644
> --- a/include/linux/pid_namespace.h
> +++ b/include/linux/pid_namespace.h
> @@ -21,6 +21,12 @@ struct pidmap {
>
>  struct fs_pin;
>
> +enum { /* definitions for pid_namespace's hide_pid field */
> +       HIDEPID_OFF       = 0,
> +       HIDEPID_NO_ACCESS = 1,
> +       HIDEPID_INVISIBLE = 2,
> +};
> +
>  struct pid_namespace {
>         struct kref kref;
>         struct pidmap pidmap[PIDMAP_ENTRIES];
> --
> 2.7.4
>



-- 
Kees Cook
Nexus Security