netdev - Re: [PATCH net] bpf: fix two bugs in verification logic when accessing 'ctx' pointer

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Message-Id: <20150416.141015.2085337707033100619.davem@davemloft.net>
Date:	Thu, 16 Apr 2015 14:10:15 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	ast@...mgrid.com
Cc:	daniel@...earbox.net, hannes@...essinduktion.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH net] bpf: fix two bugs in verification logic when
 accessing 'ctx' pointer

From: Alexei Starovoitov <ast@...mgrid.com>
Date: Wed, 15 Apr 2015 16:19:33 -0700

> 1.
> first bug is a silly mistake. It broke tracing examples and prevented
> simple bpf programs from loading.
 ...
> 2.
> second bug is more subtle.
> If malicious code is using the same dest register as source register,
> the checks designed to prevent the same instruction to be used with different
> pointer types will fail to trigger, since we were assigning src_reg_type
> when it was already overwritten by check_mem_access().
> The fix is trivial. Just move line:
> src_reg_type = regs[insn->src_reg].type;
> before check_mem_access().
> Add new 'access skb fields bad4' test to check this case.
> 
> Fixes: 9bac3d6d548e ("bpf: allow extended BPF programs access skb fields")
> Signed-off-by: Alexei Starovoitov <ast@...mgrid.com>

Applied, thank you.
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