netdev - Re: genetlink misinterprets NEW as GET

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Date:	Fri, 07 Jan 2011 13:12:25 +0100
From:	Pablo Neira Ayuso <pablo@...filter.org>
To:	Jan Engelhardt <jengelh@...ozas.de>
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 07/01/11 10:38, Jan Engelhardt wrote:
> 
> 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.

That flag combination does not make sense to me. Valid combinations are:

NLM_F_REQUEST|NLM_F_CREATE : if it does not exist, create it, if it
exists, update it.
NLM_F_REQUEST|NLM_F_CREATE|NLM_F_EXCL: if it does not exist, create it,
if it exists, return -EEXIST.
NLM_F_REQUEST|NLM_F_REPLACE: if it does not exist, return -ENOENT, if it
exists, replace it.
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