Re: [PATCH v10 06/11] seccomp: add SECCOMP_RET_ERRNO

[Will Drewry]

On Tue, Feb 21, 2012 at 4:41 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> On Tue, Feb 21, 2012 at 11:30:30AM -0600, Will Drewry wrote:
>> diff --git a/kernel/seccomp.c b/kernel/seccomp.c
>> index 0043b7e..23f1844 100644
>> --- a/kernel/seccomp.c
>> +++ b/kernel/seccomp.c
>> @@ -136,22 +136,18 @@ static void *bpf_load(const void *nr, int off, unsigned int size, void *buf)
>>  static u32 seccomp_run_filters(int syscall)
>>  {
>>       struct seccomp_filter *f;
>> -     u32 ret = SECCOMP_RET_KILL;
>>       static const struct bpf_load_fn fns = {
>>               bpf_load,
>>               sizeof(struct seccomp_data),
>>       };
>> +     u32 ret = SECCOMP_RET_ALLOW;
>>       const void *sc_ptr = (const void *)(uintptr_t)syscall;
>> -
>>       /*
>>        * All filters are evaluated in order of youngest to oldest. The lowest
>>        * BPF return value always takes priority.
>>        */
>> -     for (f = current->seccomp.filter; f; f = f->prev) {
>> -             ret = bpf_run_filter(sc_ptr, f->insns, &fns);
>> -             if (ret != SECCOMP_RET_ALLOW)
>> -                     break;
>> -     }
>> +     for (f = current->seccomp.filter; f; f = f->prev)
>> +             ret = min_t(u32, ret, bpf_run_filter(sc_ptr, f->insns, &fns));
>>       return ret;
>>  }
>
> I'd like to see this fail closed in the (theoretically impossible, but
> why risk it) case of there being no filters at all. Could do something
> like this:
>
>        u32 ret = current->seccomp.filter ? SECCOMP_RET_ALLOW : SECCOMP_RET_KILL;
>
> Or, just this, to catch the misbehavior:
>
>        if (unlikely(current->seccomp.filter == NULL))
>                return SECCOMP_RET_KILL;

I think the last one makes the most sense to me.  I'll add it and rev the patch.

thanks!
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/