linux-kernel - Re: [PATCH 4.4 106/124] netlink: Do not subscribe to non-existent groups

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Message-Id: <20180804.170753.739714742014742080.davem@davemloft.net>
Date:   Sat, 04 Aug 2018 17:07:53 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     dima@...sta.com
Cc:     natechancellor@...il.com, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        herbert@...dor.apana.org.au, steffen.klassert@...unet.com,
        netdev@...r.kernel.org
Subject: Re: [PATCH 4.4 106/124] netlink: Do not subscribe to non-existent
 groups

From: Dmitry Safonov <dima@...sta.com>
Date: Sun, 05 Aug 2018 00:44:28 +0100

> On Sat, 2018-08-04 at 16:33 -0700, David Miller wrote:
>> From: Dmitry Safonov <dima@...sta.com>
>> Date: Sun, 05 Aug 2018 00:26:38 +0100
>> 
>> > Thanks for the testing, sorry again for the breakage.
>> > Will send the patch shortly (with sizeof(unsigned long long)
>> instead of
>> > hard-coded 64). Hopefully, not too late.
>> 
>> 'groups' is "long unsigned int" not "unsigned long long"
>> 
>>         long unsigned int groups = nladdr->nl_groups;
>> 
>> And nladdr->nl_groups is specified as "__u32"
>> 
>> So the size of the relevant bits is actually strictly 32-bit.
>> 
>> This makes also the "ULL" in your constant specification incorrect as
>> well.
>> 
>> So much crazy stuff going on here :-/
> 
> Right, I misslooked that..
> How does this work on Android then?
> I doubt they changed uabi.

We can have many more than 32 multicast group subscriptions.

That's why the memberships are also stored in the nlk->groups[] array.

I'm --><--- this close to simply reverting all of your changes, the
missed masking seems to be quite harmless.