On Mon, Feb 27, 2012 at 10:14 AM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
> On 02/27, Kees Cook wrote:
>>
>> On Mon, Feb 27, 2012 at 9:11 AM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
>> > On 02/24, Will Drewry wrote:
>> >>
>> >> 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;
>> >>
>> >> + /* Ensure unexpected behavior doesn't result in failing open. */
>> >> + if (unlikely(current->seccomp.filter == NULL))
>> >> + ret = SECCOMP_RET_KILL;
>> >
>> > Is "seccomp.filter == NULL" really possible?
>>
>> It should not be, but I'm much more comfortable with this failing
>> closed. I think it's important to be as defensive as possible with
>> this code given its intended use.
>
> Can't resists... Sorry, I know I am troll but personally I think
> in this case the most defensive code is BUG_ON(->filter == NULL)
> or at least WARN_ON().
Linus will probably object because he objected (correctly) to a very
similar problem in my old vsyscall emulation series. A userspace
security feature shouldn't have a failure mode in which it confuses
the kernel and results in an oops, unless the situation is really
unrecoverable. So WARN_ON plus do_exit would be okay but BUG_ON would
not.
--Andy
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