netdev - Re: [PATCH net-next v2 4/7] net: packet: use skb->dev as storage for skb orig len instead of skb->cb[]

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Sat, 28 Feb 2015 21:39:34 +0200
From:	Eyal Birger <eyal.birger@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	Willem de Bruijn <willemb@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Shmulik Ladkani <shmulik.ladkani@...il.com>,
	linux-bluetooth@...r.kernel.org,
	Marcel Holtmann <marcel@...tmann.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next v2 4/7] net: packet: use skb->dev as storage for
 skb orig len instead of skb->cb[]

On Sat, Feb 28, 2015 at 9:21 PM, David Miller <davem@...emloft.net> wrote:
> From: Eyal Birger <eyal.birger@...il.com>
> Date: Thu, 26 Feb 2015 21:07:01 +0200
>
>> As part of an effort to move skb->dropcount to skb->cb[], 4 bytes
>> of additional room are needed in skb->cb[] in packet sockets.
>>
>> Store the skb original length in skb->dev instead of skb->cb[] for
>> this purpose.
>>
>> Signed-off-by: Eyal Birger <eyal.birger@...il.com>
>
> I'm a little confused, why is this even needed?
>
> packet_skb_cb is 24 bytes by my calculations, which is much
> smaller than the cb[] size which is 48 bytes.

Note the BUILD_BUG_ON in packet_rcv().

packet_skb_cb may contain an address as large as MAX_ADDR_LEN (32)
Therefore the required space is sizeof(packet_skb_cb) + MAX_ADDR_LEN - 8
which is 48 bytes before this change.

Regards,
Eyal.
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html