Subject: Re: [PATCH net] bpf: fix bug in eBPF verifier

From: Hannes Frederic Sowa <[email-masked]>
Date: Tue, 21 Oct 2014 12:35:42 +0200

On Mo, 2014-10-20 at 14:54 -0700, Alexei Starovoitov wrote:
> while comparing for verifier state equivalency the comparison
> was missing a check for uninitialized register.
> Make sure it does so and add a testcase.
> 
> Fixes: f1bca824dabb ("bpf: add search pruning optimization to verifier")
> Cc: Hannes Frederic Sowa <[email-masked]>
> Signed-off-by: Alexei Starovoitov <[email-masked]>
> ---
> 
> while we were staring at the verifier code with Hannes during LPC
> something felt odd in this spot. Yes. It was a bug. Fix it.
> 
>  kernel/bpf/verifier.c       |    3 ++-
>  samples/bpf/test_verifier.c |   11 +++++++++++
>  2 files changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 801f5f3..9f81818 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -1409,7 +1409,8 @@ static bool states_equal(struct verifier_state *old, struct verifier_state *cur)
>  		if (memcmp(&old->regs[i], &cur->regs[i],
>  			   sizeof(old->regs[0])) != 0) {
>  			if (old->regs[i].type == NOT_INIT ||
> -			    old->regs[i].type == UNKNOWN_VALUE)
> +			    (old->regs[i].type == UNKNOWN_VALUE &&
> +			     cur->regs[i].type != NOT_INIT))
>  				continue;
>  			return false;
>  		}

That makes sense.

Acked-by: Hannes Frederic Sowa <[email-masked]>

Thanks,
Hannes