netdev - Aw: Re: question about checksumming and tcp

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:	Fri, 6 Nov 2015 20:14:15 +0100
From:	ronny.hegewald@...ine.de
To:	"Tom Herbert" <tom@...bertland.com>
Cc:	netdev@...r.kernel.org
Subject: Aw: Re: question about checksumming and tcp_sendpage

> Well, looking at the code I don't readily see how this works either,
> but note that tcp_sendmsg has the same check also. If your analysis is
> correct then checksum for IPv6 would commonly be broken (i.e. several
> devices support IPv4 checksum but not IPv6)-- so I find that hard to
> believe so I'm probably missing something too! (at least this
> ambiguity is one more reason why we need to get rid of NETIF_F_IP_CSUM
> and NETIF_F_V6_CSUM!).

I think the checksum-building is not broken because of this on itself. The
problem i see is for example in case pages are sent from a block-device 
over the net. 

Depending on the block-device this pages might be changed at any time. 
Because of the described issue the page-data wouldn't be copied as a call 
to sock_no_sendpage would do it. So the page-data might change at any time
during or after the checksum-building. From my understanding this would just
cause a crc-error anytime after sending and would only lead to a resent 
of the data, probably with a new checksum which will then be correct So
there wouldn't be a obvious impact except some bad tcp packages.

> Can you try to verify this a bug with some testing?

Will do.
--
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