On Monday, February 10, 2020 3:05 PM, Alexey Gladkov <gladkov.alexey@xxxxxxxxx> 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@xxxxxxxxxxxx
> Cc: Andy Lutomirski luto@xxxxxxxxxx
> Signed-off-by: Djalal Harouni tixxdz@xxxxxxxxx
> Signed-off-by: Alexey Gladkov gladkov.alexey@xxxxxxxxx
>
> 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.
Jordan
