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Re: [PATCH v7 4/9] seccomp: move no_new_privs into seccomp

To: Kees Cook <keescook@chromium.org>
Subject: Re: [PATCH v7 4/9] seccomp: move no_new_privs into seccomp
From: Oleg Nesterov <oleg@redhat.com>
Date: Tue, 24 Jun 2014 21:18:15 +0200
Cc: linux-kernel@vger.kernel.org, Andy Lutomirski <luto@amacapital.net>, Alexei Starovoitov <ast@plumgrid.com>, "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>, Andrew Morton <akpm@linux-foundation.org>, Daniel Borkmann <dborkman@redhat.com>, Will Drewry <wad@chromium.org>, Julien Tinnes <jln@chromium.org>, David Drysdale <drysdale@google.com>, linux-api@vger.kernel.org, x86@kernel.org, linux-arm-kernel@lists.infradead.org, linux-mips@linux-mips.org, linux-arch@vger.kernel.org, linux-security-module@vger.kernel.org
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On 06/23, Kees Cook wrote:
>
> --- a/include/linux/seccomp.h
> +++ b/include/linux/seccomp.h
> @@ -3,6 +3,8 @@
>
>  #include <uapi/linux/seccomp.h>
>
> +#define SECCOMP_FLAG_NO_NEW_PRIVS    0       /* task may not gain privs */
> +
>  #ifdef CONFIG_SECCOMP
>
>  #include <linux/thread_info.h>
> @@ -16,6 +18,7 @@ struct seccomp_filter;
>   *         system calls available to a process.
>   * @filter: must always point to a valid seccomp-filter or NULL as it is
>   *          accessed without locking during system call entry.
> + * @flags: flags under task->sighand->siglock lock
>   *
>   *          @filter must only be accessed from the context of current as 
> there
>   *          is no read locking.
> @@ -23,6 +26,7 @@ struct seccomp_filter;
>  struct seccomp {
>       int mode;
>       struct seccomp_filter *filter;
> +     unsigned long flags;
>  };
>
>  extern int __secure_computing(int);
> @@ -51,7 +55,9 @@ static inline int seccomp_mode(struct seccomp *s)
>
>  #include <linux/errno.h>
>
> -struct seccomp { };
> +struct seccomp {
> +     unsigned long flags;
> +};

A bit messy ;)

I am wondering if we can simply do

        static inline bool current_no_new_privs(void)
        {
                if (current->no_new_privs)
                        return true;

        #ifdef CONFIG_SECCOMP
                if (test_thread_flag(TIF_SECCOMP))
                        return true;
        #endif

                return false;

             return test_bit(SECCOMP_FLAG_NO_NEW_PRIVS, &p->seccomp.flags);
        }

instead ?

Oleg.


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