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  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, 11 Apr 2014 04:44:42 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	Francois WELLENREITER <f.wellenreiter@...il.com>,
	netdev@...r.kernel.org
Subject: Re: [PATCH] ipv6: Limit mtu to 65572 bytes

On Thu, Apr 10, 2014 at 06:42:10PM -0700, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@...gle.com>
> 
> Francois reported that setting big mtu on loopback device could prevent
> tcp sessions making progress.
> 
> We do not support (yet ?) IPv6 Jumbograms and cook corrupted packets.
> 
> We must limit the IPv6 MTU to (65535 + 40) bytes in theory.
> 
> In practice, its better to align to a multiple of 4 for optimal TCP
> performance.
> 
> Tested:
> 
> ifconfig lo mtu 70000
> netperf -H ::1
> 
> Before patch :
> 
> -> Throughput :   0.05 Mbits
> 
> After patch :
> 
> -> Throughput : 36624.24 Mbits
> 
> Reported-by: Francois WELLENREITER <f.wellenreiter@...il.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Acked-by: Hannes Frederic Sowa <hannes@...essinduktion.org>

Sorry about my wrong statement earlier in this thread, you're right.

Btw. this patch fixes a flaw in the UDP output path, too, where we didn't
generate EMSGSIZE error correctly before in all cases. udp_sendmsg only checks
for INT_MAX - sizeof(udphdr) and defers further checking to ip6_append_data
which seems to be prepared for jumbograms. ;)

Very cool catch with the possible ipv4 performance improvment, too. ;)

Thanks,

  Hannes

--
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

Powered by blists - more mailing lists