On 19/04/2017 00:23, Kees Cook wrote:
> On Tue, Mar 28, 2017 at 4:46 PM, Mickaël Salaün <mic@digikod.net> wrote:
>> The semantic is unchanged. This will be useful for the Landlock
>> integration with seccomp (next commit).
>>
>> Signed-off-by: Mickaël Salaün <mic@digikod.net>
>> Cc: Kees Cook <keescook@chromium.org>
>> Cc: Andy Lutomirski <luto@amacapital.net>
>> Cc: Will Drewry <wad@chromium.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.