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Date: Sat, 23 Jan 2016 20:25:02 +0100
From: Florian Westphal <fw@strlen.de>
To: Dmitry Vyukov <dvyukov@google.com>
Cc: "David S. Miller" <davem@davemloft.net>,
        Herbert Xu <herbert@gondor.apana.org.au>, Thomas Graf <tgraf@suug.ch>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Ken-ichirou MATSUZAWA <chamaken@gmail.com>,
        Eric Dumazet <edumazet@google.com>,
        David Herrmann <dh.herrmann@gmail.com>,
        Nicolas Dichtel <nicolas.dichtel@6wind.com>,
        Florian Westphal <fw@strlen.de>, netdev <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        syzkaller <syzkaller@googlegroups.com>,
        Kostya Serebryany <kcc@google.com>,
        Alexander Potapenko <glider@google.com>,
        Sasha Levin <sasha.levin@oracle.com>, netfilter-devel@vger.kernel.org
Subject: Re: net: GPF in netlink_getsockbyportid
Message-ID: <20160123192502.GB17729@breakpoint.cc>
References: <CACT4Y+Zmwr0VbfB5RAoLTCJJAF7epZWbbMkHxtXUwvF3tXbrgQ@mail.gmail.com>
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Dmitry Vyukov <dvyukov@google.com> wrote:

[ CC nf-devel, not sure if its nfnetlink fault or NETLINK_MMAP ]

> The following program causes GPF in netlink_getsockbyportid:
> 
> // autogenerated by syzkaller (http://github.com/google/syzkaller)
> #include <pthread.h>
> #include <stdint.h>
> #include <string.h>
> #include <sys/syscall.h>
> #include <unistd.h>
> 
> int main()
> {
>   syscall(SYS_mmap, 0x20000000ul, 0xe65000ul, 0x3ul, 0x32ul,
>                  0xfffffffffffffffful, 0x0ul);
>   int fd = syscall(SYS_socket, 0x10ul, 0x803ul, 0xcul, 0, 0, 0);
>   *(uint32_t*)0x20e64000 = (uint32_t)0x28;
>   *(uint32_t*)0x20e64004 = (uint32_t)0x10;
>   *(uint64_t*)0x20e64008 = (uint64_t)0x0;
>   *(uint64_t*)0x20e64010 = (uint64_t)0x3;
>   *(uint64_t*)0x20e64018 = (uint64_t)0xfff;
>   *(uint16_t*)0x20e64020 = (uint16_t)0x5;
>   syscall(SYS_write, fd, 0x20e64000ul, 0x28ul, 0, 0, 0);
>   return 0;
> }

CONFIG_NETLINK_MMAP and nfnetlink batching strike in unison :-/

root cause is in nfnetlink_rcv_batch():

296 replay:
297         status = 0;
298 
299         skb = netlink_skb_clone(oskb, GFP_KERNEL);

The clone op doesn't copy oskb->sk, so we oops in
__netlink_alloc_skb -> netlink_getsockbyportid() when nfnetlink_rcv_batch
tries to send netlink ack.