linux-kernel - Re: net/ipv6: null-ptr-deref in ip6mr_sk

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Date:   Sun, 5 Mar 2017 12:02:48 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        James Morris <jmorris@...ei.org>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Patrick McHardy <kaber@...sh.net>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: net/ipv6: null-ptr-deref in ip6mr_sk_done

On Sun, Mar 5, 2017 at 8:54 AM, Andrey Konovalov <andreyknvl@...gle.com> wrote:
> Hi,
>
> I've got the following bug report while fuzzing the kernel with syzkaller.
> Unfortunately it's not reproducible.
>
> On commit e5d56efc97f8240d0b5d66c03949382b6d7e5570 (Feb 26).
>
> kasan: GPF could be caused by NULL-ptr deref or user memory access
> general protection fault: 0000 [#1] SMP KASAN
> Dumping ftrace buffer:
>    (ftrace buffer empty)
> Modules linked in:
> CPU: 0 PID: 14446 Comm: syz-executor6 Not tainted 4.10.0+ #82
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> task: ffff88001f311700 task.stack: ffff88001f6e8000
> RIP: 0010:ip6mr_sk_done+0x15a/0x3d0 net/ipv6/ip6mr.c:1618
> RSP: 0018:ffff88001f6ef418 EFLAGS: 00010202
> RAX: dffffc0000000000 RBX: 1ffff10003edde8c RCX: ffffc900043ee000
> RDX: 0000000000000004 RSI: ffffffff83e3b3f8 RDI: 0000000000000020
> RBP: ffff88001f6ef508 R08: fffffbfff0dcc5d8 R09: 0000000000000000
> R10: ffffffff86e62ec0 R11: 0000000000000000 R12: 0000000000000000
> R13: 0000000000000000 R14: ffff88001f6ef4e0 R15: ffff8800380a0040
> FS:  00007f7a52cec700(0000) GS:ffff88003ec00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 000000000061c500 CR3: 000000001f1ae000 CR4: 00000000000006f0
> DR0: 0000000020000000 DR1: 0000000020000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
> Call Trace:
>  rawv6_close+0x4c/0x80 net/ipv6/raw.c:1217
>  inet_release+0xed/0x1c0 net/ipv4/af_inet.c:425
>  inet6_release+0x50/0x70 net/ipv6/af_inet6.c:432
>  sock_release+0x8d/0x1e0 net/socket.c:597
>  __sock_create+0x39d/0x880 net/socket.c:1226
>  sock_create_kern+0x3f/0x50 net/socket.c:1243
>  inet_ctl_sock_create+0xbb/0x280 net/ipv4/af_inet.c:1526
>  icmpv6_sk_init+0x163/0x500 net/ipv6/icmp.c:954
>  ops_init+0x10a/0x550 net/core/net_namespace.c:115
>  setup_net+0x261/0x660 net/core/net_namespace.c:291
>  copy_net_ns+0x27e/0x540 net/core/net_namespace.c:396
> 9pnet_virtio: no channels available for device ./file1
>  create_new_namespaces+0x437/0x9b0 kernel/nsproxy.c:106
>  unshare_nsproxy_namespaces+0xae/0x1e0 kernel/nsproxy.c:205
>  SYSC_unshare kernel/fork.c:2281 [inline]
>  SyS_unshare+0x64e/0x1000 kernel/fork.c:2231
>  entry_SYSCALL_64_fastpath+0x1f/0xc2

Hmm, I think net->ipv6.mr6_tables is not initialized at that point,
ip6mr_rules_init() is not called yet, therefore on the error path when
we iterator the list, we trigger this oops. We need some other way
to check if it is initialized or not.