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Date: Tue, 21 Feb 2012 16:48:05 -0600
Message-ID: <CABqD9hburo_4Yz+figsSOExun3ckft3UrZpOZTw+aywmCKy-rg@mail.gmail.com>
Subject: Re: [PATCH v10 06/11] seccomp: add SECCOMP_RET_ERRNO
From: Will Drewry <wad@chromium.org>
To: Kees Cook <keescook@chromium.org>
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On Tue, Feb 21, 2012 at 4:41 PM, Kees Cook <keescook@chromium.org> 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!
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