netdev - Re: [PATCH v2 net-next] bpf: fix cb access in socket filter programs

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Message-Id: <20151011.044028.2103081904798346355.davem@davemloft.net>
Date:	Sun, 11 Oct 2015 04:40:28 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	ast@...mgrid.com
Cc:	luto@...capital.net, mingo@...nel.org, hannes@...essinduktion.org,
	edumazet@...gle.com, daniel@...earbox.net, keescook@...omium.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH v2 net-next] bpf: fix cb access in socket filter
 programs

From: Alexei Starovoitov <ast@...mgrid.com>
Date: Wed,  7 Oct 2015 10:55:41 -0700

> eBPF socket filter programs may see junk in 'u32 cb[5]' area,
> since it could have been used by protocol layers earlier.
> 
> For socket filter programs used in af_packet we need to clean
> 20 bytes of skb->cb area if it could be used by the program.
> For programs attached to TCP/UDP sockets we need to save/restore
> these 20 bytes, since it's used by protocol layers.
> 
> Remove SK_RUN_FILTER macro, since it's no longer used.
> 
> Long term we may move this bpf cb area to per-cpu scratch, but that
> requires addition of new 'per-cpu load/store' instructions,
> so not suitable as a short term fix.
> 
> Fixes: d691f9e8d440 ("bpf: allow programs to write to certain skb fields")
> Reported-by: Eric Dumazet <edumazet@...gle.com>
> Signed-off-by: Alexei Starovoitov <ast@...mgrid.com>
> ---
> v1->v2:
> dropped extra conditional for clearing of cb for af_packet.
> 
> Since eBPF is root only, the impact of the bug is low and
> the fix can stay in net-next.

Applied to net-next, thanks.
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