Re: [PATCH 1/2] security: let security modules use PTRACE_MODE_* with bitmasks

[Kees Cook <keescook@google.com>]

On Mon, Dec 7, 2015 at 1:25 PM, Jann Horn <jann@thejh.net> wrote:
> It looks like smack and yama weren't aware that the ptrace mode
> can have flags ORed into it - PTRACE_MODE_NOAUDIT until now, but
> only for /proc/$pid/stat, and with the PTRACE_MODE_*CREDS patch,
> all modes have flags ORed into them.
>
> Signed-off-by: Jann Horn <jann@thejh.net>

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

-Kees

> ---
>  security/smack/smack_lsm.c | 8 +++-----
>  security/yama/yama_lsm.c   | 4 ++--
>  2 files changed, 5 insertions(+), 7 deletions(-)
>
> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> index ff81026..7c57c7f 100644
> --- a/security/smack/smack_lsm.c
> +++ b/security/smack/smack_lsm.c
> @@ -398,12 +398,10 @@ static int smk_copy_relabel(struct list_head *nhead, struct list_head *ohead,
>   */
>  static inline unsigned int smk_ptrace_mode(unsigned int mode)
>  {
> -       switch (mode) {
> -       case PTRACE_MODE_READ:
> -               return MAY_READ;
> -       case PTRACE_MODE_ATTACH:
> +       if (mode & PTRACE_MODE_ATTACH)
>                 return MAY_READWRITE;
> -       }
> +       if (mode & PTRACE_MODE_READ)
> +               return MAY_READ;
>
>         return 0;
>  }
> diff --git a/security/yama/yama_lsm.c b/security/yama/yama_lsm.c
> index d3c19c9..cb6ed10 100644
> --- a/security/yama/yama_lsm.c
> +++ b/security/yama/yama_lsm.c
> @@ -281,7 +281,7 @@ static int yama_ptrace_access_check(struct task_struct *child,
>         int rc = 0;
>
>         /* require ptrace target be a child of ptracer on attach */
> -       if (mode == PTRACE_MODE_ATTACH) {
> +       if (mode & PTRACE_MODE_ATTACH) {
>                 switch (ptrace_scope) {
>                 case YAMA_SCOPE_DISABLED:
>                         /* No additional restrictions. */
> @@ -307,7 +307,7 @@ static int yama_ptrace_access_check(struct task_struct *child,
>                 }
>         }
>
> -       if (rc) {
> +       if (rc && (mode & PTRACE_MODE_NOAUDIT) == 0) {
>                 printk_ratelimited(KERN_NOTICE
>                         "ptrace of pid %d was attempted by: %s (pid %d)\n",
>                         child->pid, current->comm, current->pid);
> --
> 2.1.4
>



-- 
Kees Cook
Chrome OS & Brillo Security

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