netdev - Re: [PATCH net] bpf: fix allocation warnings in bpf maps and integer overflow

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Date:	Mon, 30 Nov 2015 15:13:47 +0100
From:	Daniel Borkmann <daniel@...earbox.net>
To:	Dmitry Vyukov <dvyukov@...gle.com>,
	syzkaller <syzkaller@...glegroups.com>
CC:	Alexei Starovoitov <alexei.starovoitov@...il.com>,
	David Miller <davem@...emloft.net>,
	Alexei Starovoitov <ast@...nel.org>,
	netdev <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Kostya Serebryany <kcc@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>
Subject: Re: [PATCH net] bpf: fix allocation warnings in bpf maps and integer
 overflow

On 11/30/2015 02:57 PM, Dmitry Vyukov wrote:
...
> kamlloc produces a WARNING if you try to allocate more than it ever
> possibly can (KMALLOC_SHIFT_MAX).

Sure, I understand that.

The kzalloc() in array_map_alloc() is however with __GFP_NOWARN flag already.
The warning only triggers in mm if:

   WARN_ON_ONCE(!(gfp_mask & __GFP_NOWARN));

Your test case is using ca.map_type = 1, which is BPF_MAP_TYPE_HASH. So on
update you're triggering the kmalloc() in htab_map_update_elem().

I'm just asking about the added change in array map.

Thanks,
Daniel
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