netdev - Re: [PATCH v1 net] packet: handle too big packets for PACKET

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Message-Id: <20140821.164511.894966250481146327.davem@davemloft.net>
Date:	Thu, 21 Aug 2014 16:45:11 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	hannes@...essinduktion.org, dborkman@...hat.com,
	nhorman@...driver.com, brouer@...hat.com, netdev@...r.kernel.org,
	guy@...m.mit.edu
Subject: Re: [PATCH v1 net] packet: handle too big packets for PACKET_V3

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Fri, 15 Aug 2014 09:16:04 -0700

> From: Eric Dumazet <edumazet@...gle.com>
> 
> af_packet can currently overwrite kernel memory by out of bound
> accesses, because it assumed a [new] block can always hold one frame.
> 
> This is not generally the case, even if most existing tools do it right.
> 
> This patch clamps too long frames as API permits, and issue a one time
> error on syslog.
> 
> [  394.357639] tpacket_rcv: packet too big, clamped from 5042 to 3966. macoff=82
> 
> In this example, packet header tp_snaplen was set to 3966,
> and tp_len was set to 5042 (skb->len)
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Fixes: f6fb8f100b80 ("af-packet: TPACKET_V3 flexible buffer implementation.")

Since both the skb->len and the snaplen are provided to the user in
the ring entry descriptor, it is correct to fix this problem by simply
truncating.

Applied and queued up for -stable, thanks a lot Eric.
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