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!
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