netdev - Re: [PATCH net][v2] bpf: fix states equal logic for varlen access

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Message-ID: <20161129185221.GB22581@ast-mbp.thefacebook.com>
Date:   Tue, 29 Nov 2016 10:52:23 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Josef Bacik <jbacik@...com>
Cc:     davem@...emloft.net, netdev@...r.kernel.org, ast@...nel.org,
        jannh@...gle.com, daniel@...earbox.net, kernel-team@...com
Subject: Re: [PATCH net][v2] bpf: fix states equal logic for varlen access

On Tue, Nov 29, 2016 at 12:27:09PM -0500, Josef Bacik wrote:
> If we have a branch that looks something like this
> 
> int foo = map->value;
> if (condition) {
>   foo += blah;
> } else {
>   foo = bar;
> }
> map->array[foo] = baz;
> 
> We will incorrectly assume that the !condition branch is equal to the condition
> branch as the register for foo will be UNKNOWN_VALUE in both cases.  We need to
> adjust this logic to only do this if we didn't do a varlen access after we
> processed the !condition branch, otherwise we have different ranges and need to
> check the other branch as well.
> 
> Fixes: 484611357c19 ("bpf: allow access into map value arrays")
> Reported-by: Jann Horn <jannh@...gle.com>
> Signed-off-by: Josef Bacik <jbacik@...com>

Thank you!
Acked-by: Alexei Starovoitov <ast@...nel.org>