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Date: Mon, 30 Nov 2015 15:13:47 +0100
From: Daniel Borkmann <daniel@iogearbox.net>
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To: Dmitry Vyukov <dvyukov@google.com>, syzkaller <syzkaller@googlegroups.com>
CC: Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        David Miller <davem@davemloft.net>,
        Alexei Starovoitov <ast@kernel.org>, netdev <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Kostya Serebryany <kcc@google.com>,
        Alexander Potapenko <glider@google.com>,
        Eric Dumazet <edumazet@google.com>,
        Sasha Levin <sasha.levin@oracle.com>
Subject: Re: [PATCH net] bpf: fix allocation warnings in bpf maps and integer
 overflow
References: <CACT4Y+b1k7Ofvn6xa=qWv9xP6BbteWOnZsJMXLZ=GOby-ajF=w@mail.gmail.com> <20151130005934.GA95228@ast-mbp.thefacebook.com> <565C549C.5080408@iogearbox.net> <CACT4Y+aGR2p6VCLgqg5otFU+0unPGp4rYe9jyCGLL1hg8D5_vA@mail.gmail.com>
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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