netdev - Re: [PATCH net 1/2] net: cls_bpf: fix size mismatch on filter preparation

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Date:	Thu, 22 Jan 2015 08:39:59 -0800
From:	Alexei Starovoitov <alexei.starovoitov@...il.com>
To:	Daniel Borkmann <dborkman@...hat.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Jiří Pírko <jiri@...nulli.us>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net 1/2] net: cls_bpf: fix size mismatch on filter preparation

On Thu, Jan 22, 2015 at 1:41 AM, Daniel Borkmann <dborkman@...hat.com> wrote:
> In cls_bpf_modify_existing(), we read out the number of filter blocks,
> do some sanity checks, allocate a block on that size, and copy over the
> BPF instruction blob from user space, then pass everything through the
> classic BPF checker prior to installation of the classifier.
>
> We should reject mismatches here, there are 2 scenarios: the number of
> filter blocks could be smaller than the provided instruction blob, so
> we do a partial copy of the BPF program, and thus the instructions will
> either be rejected from the verifier or a valid BPF program will be run;
> in the other case, we'll end up copying more than we're supposed to,
> and most likely the trailing garbage will be rejected by the verifier
> as well (i.e. we need to fit instruction pattern, ret {A,K} needs to be
> last instruction, load/stores must be correct, etc); in case not, we
> would leak memory when dumping back instruction patterns. The code should
> have only used nla_len() as Dave noted to avoid this from the beginning.
> Anyway, lets fix it by rejecting such load attempts.
>
> Fixes: 7d1d65cb84e1 ("net: sched: cls_bpf: add BPF-based classifier")
> Signed-off-by: Daniel Borkmann <dborkman@...hat.com>
> Acked-by: Jiri Pirko <jiri@...nulli.us>

Acked-by: Alexei Starovoitov <ast@...mgrid.com>
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