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SubjectRe: [PATCH v8 08/11] proc: instantiate only pids that we can ptrace on 'hidepid=4' mount option
On Mon, Feb 10, 2020 at 04:29:31PM +0000, Jordan Glover wrote:
> On Monday, February 10, 2020 3:05 PM, Alexey Gladkov <gladkov.alexey@gmail.com> wrote:
>
> > If "hidepid=4" mount option is set then do not instantiate pids that
> > we can not ptrace. "hidepid=4" means that procfs should only contain
> > pids that the caller can ptrace.
> >
> > Cc: Kees Cook keescook@chromium.org
> > Cc: Andy Lutomirski luto@kernel.org
> > Signed-off-by: Djalal Harouni tixxdz@gmail.com
> > Signed-off-by: Alexey Gladkov gladkov.alexey@gmail.com
> >
> > fs/proc/base.c | 15 +++++++++++++++
> > fs/proc/root.c | 14 +++++++++++---
> > include/linux/proc_fs.h | 1 +
> > 3 files changed, 27 insertions(+), 3 deletions(-)
> >
> > diff --git a/fs/proc/base.c b/fs/proc/base.c
> > index 24b7c620ded3..49937d54e745 100644
> > --- a/fs/proc/base.c
> > +++ b/fs/proc/base.c
> > @@ -699,6 +699,14 @@ static bool has_pid_permissions(struct proc_fs_info *fs_info,
> > struct task_struct *task,
> > int hide_pid_min)
> > {
> >
> > - /*
> > - - If 'hidpid' mount option is set force a ptrace check,
> > - - we indicate that we are using a filesystem syscall
> > - - by passing PTRACE_MODE_READ_FSCREDS
> > - */
> > - if (proc_fs_hide_pid(fs_info) == HIDEPID_NOT_PTRACABLE)
> > - return ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS);
> >
> >
> > - if (proc_fs_hide_pid(fs_info) < hide_pid_min)
> > return true;
> > if (in_group_p(proc_fs_pid_gid(fs_info)))
> > @@ -3271,7 +3279,14 @@ struct dentry *proc_pid_lookup(struct dentry *dentry, unsigned int flags)
> > if (!task)
> > goto out;
> >
> > - /* Limit procfs to only ptracable tasks */
> > - if (proc_fs_hide_pid(fs_info) == HIDEPID_NOT_PTRACABLE) {
> > - if (!has_pid_permissions(fs_info, task, HIDEPID_NO_ACCESS))
> >
> >
> > - goto out_put_task;
> >
> >
> > - }
> > - result = proc_pid_instantiate(dentry, task, NULL);
> > +out_put_task:
> > put_task_struct(task);
> > out:
> > return result;
> > diff --git a/fs/proc/root.c b/fs/proc/root.c
> > index e2bb015da1a8..5e27bb31f125 100644
> > --- a/fs/proc/root.c
> > +++ b/fs/proc/root.c
> > @@ -52,6 +52,15 @@ static const struct fs_parameter_description proc_fs_parameters = {
> > .specs = proc_param_specs,
> > };
> >
> > +static inline int
> > +valid_hidepid(unsigned int value)
> > +{
> >
> > - return (value == HIDEPID_OFF ||
> > - value == HIDEPID_NO_ACCESS ||
> >
> >
> > - value == HIDEPID_INVISIBLE ||
> >
> >
> > - value == HIDEPID_NOT_PTRACABLE);
> >
> >
> >
> > +}
> > +
> > static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param)
> > {
> > struct proc_fs_context *ctx = fc->fs_private;
> > @@ -68,10 +77,9 @@ static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param)
> > break;
> >
> > case Opt_hidepid:
> >
> > - if (!valid_hidepid(result.uint_32))
> >
> >
> > - return invalf(fc, "proc: unknown value of hidepid.\\n");
> > ctx->hidepid = result.uint_32;
> >
> >
> >
> > - if (ctx->hidepid < HIDEPID_OFF ||
> >
> >
> > - ctx->hidepid > HIDEPID_INVISIBLE)
> >
> >
> > - return invalf(fc, "proc: hidepid value must be between 0 and 2.\\n");
> > break;
> >
> >
> >
> > default:
> > diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
> > index f307940f8311..6822548405a7 100644
> > --- a/include/linux/proc_fs.h
> > +++ b/include/linux/proc_fs.h
> > @@ -17,6 +17,7 @@ enum {
> > HIDEPID_OFF = 0,
> > HIDEPID_NO_ACCESS = 1,
> > HIDEPID_INVISIBLE = 2,
> >
> > - HIDEPID_NOT_PTRACABLE = 4, /* Limit pids to only ptracable pids */
>
> Is there a reason new option is "4" instead of "3"? The order 1..2..4 may be
> confusing for people.

This is just mask. For now hidepid values are mutually exclusive, but
since it moved to uapi, I thought it would be good if there was an
opportunity to combine values.

--
Rgrds, legion

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