netdev - Re: genetlink misinterprets NEW as GET

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Message-ID: <alpine.LNX.2.01.1101071033400.25363@obet.zrqbmnf.qr>
Date:	Fri, 7 Jan 2011 10:38:49 +0100 (CET)
From:	Jan Engelhardt <jengelh@...ozas.de>
To:	Pablo Neira Ayuso <pablo@...filter.org>
cc:	Ben Pfaff <blp@...ira.com>,
	Netfilter Developer Mailing List 
	<netfilter-devel@...r.kernel.org>,
	Linux Networking Developer Mailing List 
	<netdev@...r.kernel.org>
Subject: Re: genetlink misinterprets NEW as GET


On Friday 2011-01-07 02:31, Pablo Neira Ayuso wrote:
>>>> 	/* Modifiers to GET request */
>>>> 	#define NLM_F_ROOT      0x100
>>>> 	#define NLM_F_MATCH     0x200
>>>> 	#define NLM_F_ATOMIC    0x400
>>>> 	#define NLM_F_DUMP      (NLM_F_ROOT|NLM_F_MATCH)
>> [...]
>>>> [N.B.: I am also wondering whether
>>>> 	(nlh->nlmsg_flags & NLM_F_DUMP) == NLM_F_DUMP
>>>> may have been desired, because NLM_F_DUMP is composed of two bits.]
>>>
>>> Someone may include NLM_F_ATOMIC to a dump operation, in that case the
>>> checking that you propose is not valid.
>> 
>> Are you saying that NLM_F_MATCH and NLM_F_ATOMIC are mutually
>> exclusive, and that NLM_F_ROOT|NLM_F_ATOMIC would also signal a
>> dump operation?  Otherwise the test that Jan proposes looks valid
>> to me.
>
>Indeed, Jan's test is fine to fix this. Please, send a patch to Davem asap.

But that would still mean that a user sending a
NLM_F_REQUEST|NLM_F_REPLACE|NLM_F_EXCL message would be misinterpreted
as NLM_F_DUMP.
There just is no way for genl to figure out from an arbitrary nlmsghdr
whether it's a dump request or something else without breaking 
something.
The overlapping of NLM_F_ is quite unfortunate.
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