netdev - Re: 4.1+ use after free in netlink_broadcast

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Date:	Fri, 26 Jun 2015 10:33:12 -0400
From:	Craig Gallek <kraig@...gle.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Dave Jones <davej@...emonkey.org.uk>, netdev@...r.kernel.org
Subject: Re: 4.1+ use after free in netlink_broadcast_filtered

On Fri, Jun 26, 2015 at 1:17 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Fri, 2015-06-26 at 00:44 -0400, Dave Jones wrote:
>> I taught Trinity about NETLINK_LISTEN_ALL_NSID and NETLINK_LIST_MEMBERSHIPS
>> yesterday, and this evening, this fell out..
>>
>> general protection fault: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
>> CPU: 1 PID: 9130 Comm: kworker/1:1 Not tainted 4.1.0-gelk-debug+ #1
>> Workqueue: sock_diag_events sock_diag_broadcast_destroy_work
>> task: ffff8800b94e4c40 ti: ffff8800352ec000 task.ti: ffff8800352ec000
>> RIP: 0010:[<ffffffff845c82e4>]  [<ffffffff845c82e4>] netlink_broadcast_filtered+0x24/0x3b0
>> RSP: 0000:ffff8800352efd08  EFLAGS: 00010292
>> RAX: ffff8800ab903d80 RBX: 0000000000000003 RCX: 0000000000000003
>> RDX: 0000000000000000 RSI: 00000000000000d0 RDI: ffff8800b9c586c0
>> RBP: ffff8800352efd78 R08: 00000000000000d0 R09: 0000000000000000
>> R10: 0000000000000000 R11: 0000000000000220 R12: 0000000000000000
>> R13: 6b6b6b6b6b6b6b6b R14: 0000000000000003 R15: 0000000000000000
>> FS:  0000000000000000(0000) GS:ffff8800bf700000(0000) knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
>> CR2: 0000000002121ff8 CR3: 0000000030169000 CR4: 00000000000007e0
>> DR0: 00007fe1f0454000 DR1: 0000000000000000 DR2: 0000000000000000
>> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
>> Stack:
>>  ffff8800b9c586c0 ffff8800b9c586c0 ffff8800ac4692c0 ffff8800936d4a90
>>  ffff8800352efd38 ffffffff8469a93e ffff8800352efd98 ffffffffc09b9b90
>>  ffff8800352efd78 ffff8800ac4692c0 ffff8800b9c586c0 ffff8800831b6ab8
>> Call Trace:
>>  [<ffffffff8469a93e>] ? mutex_unlock+0xe/0x10
>>  [<ffffffffc09b9b90>] ? inet_diag_handler_get_info+0x110/0x1fb [inet_diag]
>>  [<ffffffff845c868d>] netlink_broadcast+0x1d/0x20
>>  [<ffffffff8469a93e>] ? mutex_unlock+0xe/0x10
>>  [<ffffffff845b2bf5>] sock_diag_broadcast_destroy_work+0xd5/0x160
>>  [<ffffffff8408ea97>] process_one_work+0x147/0x420
>>  [<ffffffff8408f0f9>] worker_thread+0x69/0x470
>>  [<ffffffff8409fda3>] ? preempt_count_sub+0xa3/0xf0
>>  [<ffffffff8408f090>] ? rescuer_thread+0x320/0x320
>>  [<ffffffff84093cd7>] kthread+0x107/0x120
>>  [<ffffffff84093bd0>] ? kthread_create_on_node+0x1b0/0x1b0
>>  [<ffffffff8469d31f>] ret_from_fork+0x3f/0x70
>>  [<ffffffff84093bd0>] ? kthread_create_on_node+0x1b0/0x1b0
>> Code: 1f 84 00 00 00 00 00 66 66 66 66 90 55 48 89 e5 41 57 41 56 41 55 49 89 fd 48 89 f7 44 89 c6 41 54 41 89 d4 53 89 cb 48 83 ec 48 <49> 8b 45 30 44 89 45 a4 4c 89 4d 98 48 89 45 c0 e8 07 f6 ff ff
>> RIP  [<ffffffff845c82e4>] netlink_broadcast_filtered+0x24/0x3b0
>>  RSP <ffff8800352efd08>
>> ---[ end trace e2d8a07893775a9e ]---
>>
>>
>> r13 looks like slab poison, and the decoded instruction shows..
>>
>>
>> int netlink_broadcast_filtered(struct sock *ssk, struct sk_buff *skb, u32 portid,
>>         u32 group, gfp_t allocation,
>>         int (*filter)(struct sock *dsk, struct sk_buff *skb, void *data),
>>         void *filter_data)
>> {
>>     1b70:       e8 00 00 00 00          callq  1b75 <netlink_broadcast_filtered+0x5>
>>     1b75:       55                      push   %rbp
>>     1b76:       48 89 e5                mov    %rsp,%rbp
>>     1b79:       41 57                   push   %r15
>>     1b7b:       41 56                   push   %r14
>>     1b7d:       41 55                   push   %r13
>>     1b7f:       49 89 fd                mov    %rdi,%r13
>>     1b82:       48 89 f7                mov    %rsi,%rdi
>>     1b85:       44 89 c6                mov    %r8d,%esi
>>     1b88:       41 54                   push   %r12
>>     1b8a:       41 89 d4                mov    %edx,%r12d
>>     1b8d:       53                      push   %rbx
>>     1b8e:       89 cb                   mov    %ecx,%ebx
>>     1b90:       48 83 ec 48             sub    $0x48,%rsp
>>     1b94:       49 8b 45 30             mov    0x30(%r13),%rax    <--  trapping instruction
>>     1b98:       44 89 45 a4             mov    %r8d,-0x5c(%rbp)
>>     1b9c:       4c 89 4d 98             mov    %r9,-0x68(%rbp)
>>     1ba0:       48 89 45 c0             mov    %rax,-0x40(%rbp)
>>         struct net *net = sock_net(ssk);
>>
>>
>> So it looks like the ssk we passed in was already freed.
>> I'll dig into this some more next week, and try to find a better
>> reproducer.
Thanks for the pointer.  In this stack, I believe ssk should always be
diag_nlsk from the struct net associated with a sock that is being
destroyed.  Given that diag_nlsk is created/destroyed via __net_init
and __net_exit and that this broadcast work happens out of band in a
work queue, it seems possible that the destruction of a given
diag_nlsk can race with a socked destruction event.

I'll try to reproduce it and send a fix as soon as I confirm.  I think
a simple fix may be to change the nlmsg_multicast  line in
sock_diag_broadcast_destroy_work to use init_net instead of the per
socket namespace.

>
> CC Craig
>
> Thanks for the report Dave.
>
>
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