Subject: Re: [PATCH bpf] bpf: fix sanitation rewrite in case of non-pointers

From: Jakub Sitnicki <[email-masked]>
Date: Tue, 05 Mar 2019 15:12:27 +0100

On Fri, Mar 01, 2019 at 10:05 PM CET, Daniel Borkmann wrote:
> Marek reported that he saw an issue with the below snippet in that
> timing measurements where off when loaded as unpriv while results
> were reasonable when loaded as privileged:
>
>     [...]
>     uint64_t a = bpf_ktime_get_ns();
>     uint64_t b = bpf_ktime_get_ns();
>     uint64_t delta = b - a;
>     if ((int64_t)delta > 0) {
>     [...]
>
> Turns out there is a bug where a corner case is missing in the fix
> d3bd7413e0ca ("bpf: fix sanitation of alu op with pointer / scalar
> type from different paths"), namely fixup_bpf_calls() only checks
> whether aux has a non-zero alu_state, but it also needs to test for
> the case of BPF_ALU_NON_POINTER since in both occasions we need to
> skip the masking rewrite (as there is nothing to mask).
>
> Fixes: d3bd7413e0ca ("bpf: fix sanitation of alu op with pointer / scalar type from different paths")
> Reported-by: Marek Majkowski <[email-masked]>
> Reported-by: Arthur Fabre <[email-masked]>
> Signed-off-by: Daniel Borkmann <[email-masked]>
> Link: https://lore.kernel.org/netdev/[email-masked]/T/
> ---

Could you please queue it for -stable which has d3bd7413e0ca ("bpf: fix
sanitation of alu op with pointer / scalar type from different paths")?

Thanks,
Jakub