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] [day] [month] [year] [list]
Date:	Mon, 27 Jan 2014 12:57:46 -0800 (PST)
From:	David Miller <>
Subject: Re: [PATCH V4] net: ip, ipv6: handle gso skbs in forwarding path

From: Florian Westphal <>
Date: Mon, 27 Jan 2014 18:58:12 +0100

> Marcelo Ricardo Leitner reported problems when the forwarding link
> path has a lower mtu than the incoming link if the inbound interface
> supports GRO.
> Given:
> Host <mtu1500> R1 <mtu1200> R2
> Host sends tcp stream which is routed via R1 and R2.  R1 performs GRO.
> In this case, the kernel will fail to send ICMP fragmentation needed
> messages (or pkt too big for ipv6), as gso packets currently bypass the
> dst mtu checks in forward path. Instead, Linux tries to send out packets
> exceeding R1-R2 link mtu.
> When locking route MTU on Host (i.e., no ipv4 DF bit set), R1 does
> not fragment the packets when forwarding, and again tries to send out
> packets exceeding R1-R2 link mtu.
> This alters the forwarding dstmtu checks to take the individual gso
> segment lengths into account.
> For ipv6, we send out pkt too big error for gso if the individual
> segments are too big.
> For ipv4, we either send icmp fragmentation needed, or, if the DF bit
> is not set, perform software segmentation and let the output path
> create fragments when the packet is leaving the machine.
> It is not 100% correct as the error message will contain the headers of
> the GRO skb instead of the original/segmented one, but it seems to
> work fine in my (limited) tests.
> Signed-off-by: Florian Westphal <>

Applied, thanks.
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to
More majordomo info at

Powered by blists - more mailing lists