netdev - Re: Netlink limitations

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:	Tue, 09 Nov 2010 13:24:26 +0100
From:	Patrick McHardy <kaber@...sh.net>
To:	Jan Engelhardt <jengelh@...ozas.de>
CC:	"David S. Miller" <davem@...emloft.net>,
	Holger Eitzenberger <heitzenberger@...aro.com>,
	Pablo Neira Ayuso <pablo@...filter.org>,
	netdev@...r.kernel.org
Subject: Re: Netlink limitations

Am 09.11.2010 13:10, schrieb Jan Engelhardt:
> 
> On Sunday 2010-11-07 18:17, Patrick McHardy wrote:
>> On 07.11.2010 17:44, Jan Engelhardt wrote:
>>> we mentioned it only briefly at the Netfilter workshop a few weeks ago, 
>>> but as I am trying to figure out how to use Netlink in Xtables, 
>>> Netlink's limitations really start ruining my day.
>>>
>>> The well-known issue is that NL messages[sic] the kernel is supposed to 
>>> receive have a max size of 64K, due to nlmsghdr's use of uint16_t. This 
>>> is very problematic because attributes can easily amass more than 64K. 
>>> Think of a chain full of rules, represented by a top-level attribute 
>>> that nests attributes. The problem is bidirectional, a table 
>>> dump has the same problem.
>>
>> Messages are not limited to 64k, individual attributes are. Holger
>> started working on a nlattr32, which uses 32 bit for the length
>> value.
> 
> Does he have a format specification available?

As I said, the basic idea is to use a length value of zero to indicate
that the length should be read from a second length member. Basically:

struct nlattr32 {
	__u16 nla_len;
	__u16 nla_type;
	__u32 nla_len2;
};

--
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