netdev - Re: [PATCH net-next v6 05/11] seccomp: Split put_seccomp_filter() with put

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Message-ID: <CAGXu5jLaYXE14AKL5Za5BKUJx9qBdcsdyJEzh5ffN4BUxkCzBA@mail.gmail.com>
Date:   Wed, 19 Apr 2017 18:54:33 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Mickaël Salaün <mic@...ikod.net>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Andy Lutomirski <luto@...capital.net>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        David Drysdale <drysdale@...gle.com>,
        "David S . Miller" <davem@...emloft.net>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        James Morris <james.l.morris@...cle.com>,
        Jann Horn <jann@...jh.net>, Jonathan Corbet <corbet@....net>,
        Matthew Garrett <mjg59@...f.ucam.org>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Paul Moore <paul@...l-moore.com>,
        Sargun Dhillon <sargun@...gun.me>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        Shuah Khan <shuah@...nel.org>, Tejun Heo <tj@...nel.org>,
        Thomas Graf <tgraf@...g.ch>, Will Drewry <wad@...omium.org>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        Linux API <linux-api@...r.kernel.org>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next v6 05/11] seccomp: Split put_seccomp_filter()
 with put_seccomp()

On Wed, Apr 19, 2017 at 3:18 PM, Mickaël Salaün <mic@...ikod.net> wrote:
>
> On 19/04/2017 00:47, Mickaël Salaün wrote:
>>
>> On 19/04/2017 00:23, Kees Cook wrote:
>>> On Tue, Mar 28, 2017 at 4:46 PM, Mickaël Salaün <mic@...ikod.net> wrote:
>>>> The semantic is unchanged. This will be useful for the Landlock
>>>> integration with seccomp (next commit).
>>>>
>>>> Signed-off-by: Mickaël Salaün <mic@...ikod.net>
>>>> Cc: Kees Cook <keescook@...omium.org>
>>>> Cc: Andy Lutomirski <luto@...capital.net>
>>>> Cc: Will Drewry <wad@...omium.org>
>>>> ---
>>>>  include/linux/seccomp.h |  4 ++--
>>>>  kernel/fork.c           |  2 +-
>>>>  kernel/seccomp.c        | 18 +++++++++++++-----
>>>>  3 files changed, 16 insertions(+), 8 deletions(-)
>>>>
>>>> diff --git a/include/linux/seccomp.h b/include/linux/seccomp.h
>>>> index ecc296c137cd..e25aee2cdfc0 100644
>>>> --- a/include/linux/seccomp.h
>>>> +++ b/include/linux/seccomp.h
>>>> @@ -77,10 +77,10 @@ static inline int seccomp_mode(struct seccomp *s)
>>>>  #endif /* CONFIG_SECCOMP */
>>>>
>>>>  #ifdef CONFIG_SECCOMP_FILTER
>>>> -extern void put_seccomp_filter(struct task_struct *tsk);
>>>> +extern void put_seccomp(struct task_struct *tsk);
>>>>  extern void get_seccomp_filter(struct task_struct *tsk);
>>>>  #else  /* CONFIG_SECCOMP_FILTER */
>>>> -static inline void put_seccomp_filter(struct task_struct *tsk)
>>>> +static inline void put_seccomp(struct task_struct *tsk)
>>>>  {
>>>>         return;
>>>>  }
>>>> diff --git a/kernel/fork.c b/kernel/fork.c
>>>> index 6c463c80e93d..a27d8e67ce33 100644
>>>> --- a/kernel/fork.c
>>>> +++ b/kernel/fork.c
>>>> @@ -363,7 +363,7 @@ void free_task(struct task_struct *tsk)
>>>>  #endif
>>>>         rt_mutex_debug_task_free(tsk);
>>>>         ftrace_graph_exit_task(tsk);
>>>> -       put_seccomp_filter(tsk);
>>>> +       put_seccomp(tsk);
>>>>         arch_release_task_struct(tsk);
>>>>         if (tsk->flags & PF_KTHREAD)
>>>>                 free_kthread_struct(tsk);
>>>> diff --git a/kernel/seccomp.c b/kernel/seccomp.c
>>>> index 65f61077ad50..326f79e32127 100644
>>>> --- a/kernel/seccomp.c
>>>> +++ b/kernel/seccomp.c
>>>> @@ -64,6 +64,8 @@ struct seccomp_filter {
>>>>  /* Limit any path through the tree to 256KB worth of instructions. */
>>>>  #define MAX_INSNS_PER_PATH ((1 << 18) / sizeof(struct sock_filter))
>>>>
>>>> +static void put_seccomp_filter(struct seccomp_filter *filter);
>>>
>>> Can this be reorganized easily to avoid a forward-declaration?
>>
>> I didn't want to move too much code but I will.
>>
>>>
>>>> +
>>>>  /*
>>>>   * Endianness is explicitly ignored and left for BPF program authors to manage
>>>>   * as per the specific architecture.
>>>> @@ -314,7 +316,7 @@ static inline void seccomp_sync_threads(void)
>>>>                  * current's path will hold a reference.  (This also
>>>>                  * allows a put before the assignment.)
>>>>                  */
>>>> -               put_seccomp_filter(thread);
>>>> +               put_seccomp_filter(thread->seccomp.filter);
>>>>                 smp_store_release(&thread->seccomp.filter,
>>>>                                   caller->seccomp.filter);
>>>>
>>>> @@ -476,10 +478,11 @@ static inline void seccomp_filter_free(struct seccomp_filter *filter)
>>>>         }
>>>>  }
>>>>
>>>> -/* put_seccomp_filter - decrements the ref count of tsk->seccomp.filter */
>>>> -void put_seccomp_filter(struct task_struct *tsk)
>>>> +/* put_seccomp_filter - decrements the ref count of a filter */
>>>> +static void put_seccomp_filter(struct seccomp_filter *filter)
>>>>  {
>>>> -       struct seccomp_filter *orig = tsk->seccomp.filter;
>>>> +       struct seccomp_filter *orig = filter;
>>>> +
>>>>         /* Clean up single-reference branches iteratively. */
>>>>         while (orig && atomic_dec_and_test(&orig->usage)) {
>>>>                 struct seccomp_filter *freeme = orig;
>>>> @@ -488,6 +491,11 @@ void put_seccomp_filter(struct task_struct *tsk)
>>>>         }
>>>>  }
>>>>
>>>> +void put_seccomp(struct task_struct *tsk)
>>>> +{
>>>> +       put_seccomp_filter(tsk->seccomp.filter);
>>>> +}
>>>> +
>>>>  static void seccomp_init_siginfo(siginfo_t *info, int syscall, int reason)
>>>>  {
>>>>         memset(info, 0, sizeof(*info));
>>>> @@ -914,7 +922,7 @@ long seccomp_get_filter(struct task_struct *task, unsigned long filter_off,
>>>>         if (copy_to_user(data, fprog->filter, bpf_classic_proglen(fprog)))
>>>>                 ret = -EFAULT;
>>>>
>>>> -       put_seccomp_filter(task);
>>>> +       put_seccomp_filter(task->seccomp.filter);
>>>>         return ret;
>>>
>>> I don't like that the arguments to get_seccomp_filter() and
>>> put_seccomp_filter() are now different. I think they should match for
>>> readability.
>>
>> OK, I can do that.
>>
>
> Kees, can I send this as a separate patch?

Sure! Though I still think the argument to get/put_seccomp_filter()
should be task_struct.

-Kees

-- 
Kees Cook
Pixel Security