On Mon, Mar 04, 2019 at 01:38:56PM +0100, Daniel Borkmann wrote:
> commit 3612af783cf52c74a031a2f11b82247b2599d3cd upstream.
>
> 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 <marek@xxxxxxxxxxxxxx>
> Reported-by: Arthur Fabre <afabre@xxxxxxxxxxxxxx>
> Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
> Link: https://lore.kernel.org/netdev/CAJPywTJqP34cK20iLM5YmUMz9KXQOdu1-+BZrGMAGgLuBWz7fg@xxxxxxxxxxxxxx/T/
> Acked-by: Song Liu <songliubraving@xxxxxx>
> Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
> Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
> ---
> kernel/bpf/verifier.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 4d81be2..bcb42aa 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -6035,7 +6035,8 @@ static int fixup_bpf_calls(struct bpf_verifier_env *env)
> u32 off_reg;
>
> aux = &env->insn_aux_data[i + delta];
> - if (!aux->alu_state)
> + if (!aux->alu_state ||
> + aux->alu_state == BPF_ALU_NON_POINTER)
> continue;
>
> isneg = aux->alu_state & BPF_ALU_NEG_VALUE;
> --
> 2.9.5
>
Thanks, now queued up.
greg k-h
