linux-kernel - Re: [PATCH] lro: IP fragment checking

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] [day] [month] [year] [list]

Date:	Tue, 02 Dec 2008 10:36:22 -0500
From:	Andrew Gallatin <gallatin@...i.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
CC:	David Miller <davem@...emloft.net>, ossthema@...ibm.com,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	tklein@...ibm.com, raisch@...ibm.com, jb.billaud@...il.com,
	hering2@...ibm.com
Subject: Re: [PATCH] lro: IP fragment checking

Ben Hutchings wrote:
> On Tue, 2008-12-02 at 09:42 -0500, Andrew Gallatin wrote:
>> Ben Hutchings wrote:
>>> On Mon, 2008-12-01 at 19:02 -0500, Andrew Gallatin wrote:
>>>> Ben Hutchings wrote:
> [...]
>>>>> If your hardware/firmware wrongly claims to be able to verify the
>>>>> TCP/UDP checksum for an IP fragment, it seems to me you should deal with
>>>>> that in your driver or fix the firmware.
>>>> We do partial checksums.
>>> So you should check for IP fragmentation in your get_frag_header() along
>>> with all the other checks you've got to do.
>> Indeed, and that is the patch I intend to submit if the fragment
>> check in inet_lro is rejected.  I still think the check belongs
>> in the inet lro code though, and I'm worried it is being rejected
>> for the wrong reasons..
> 
> There's a wide variety of capabilities of different hardware:
> 
> 1. No checksum offload. Probably not worth using LRO.
> 2. Full-checksum generation. Driver passes packets to inet_lro;
> get_frag_header() or get_skb_header() parses packets to check that they
> are TCP/IPv4 and to validate the checksum. inet_lro does further checks.
> 3. L4 packet parsing and checksum validation. Driver passes TCP/IPv4
> packets to inet_lro. inet_lro does further checks.
> 4. Hardware/firmware LRO. inet_lro not needed.
> 
> You seem to be proposing that a check that is only needed in case (2)
> should also be applied in case (3).  Maybe it would make more sense to
> define a generic implementation of get_frag_header() for full-checksum
> devices, if that's possible?

Or maybe a generic lro_check_header() that can be called from
everybody's get_frag_header()/get_skb_header().  I guess what
bothers me is the division of checks between the get_*_header()
routine and lro_tcp_ip_checks() and the inevitable code
duplication in the get_*_header routines.

I still don't understand why an unneeded check for fragmentation
in case (3) is any more objectionable than the existing tcp
flags checks in lro_tcp_ip_check(), many of which are surely
not needed in case (3) either.

Drew
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/