[Bridge] Use-after-free in br_multicast_rcv

[nikolay at cumulusnetworks.com]

On 29 June 2019 14:54:44 EEST, Martin Weinelt <martin at linuxlounge.net> wrote:
>Hello,
>
>we've recently been experiencing memory leaks on our Linux-based
>routers,
>at least as far back as v4.19.16.
>
>After rebuilding with KASAN it found a use-after-free in 
>br_multicast_rcv which I could reproduce on v5.2.0-rc6. 
>
>Please find the KASAN report below, I'm anot sure what else to provide
>so
>feel free to ask.
>
>Best,
>  Martin
>
>

Hi Martin, 
I'll look into this, are there any specific steps to reproduce it? 

Thanks, 
   Nik

>==================================================================
>BUG: KASAN: use-after-free in br_multicast_rcv+0x480c/0x4ad0 [bridge]
>Read of size 2 at addr ffff8880421302b4 by task ksoftirqd/1/16
>
>CPU: 1 PID: 16 Comm: ksoftirqd/1 Tainted: G           OE     5.2.0-rc6+
>#1
>Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1
>04/01/2014
>Call Trace:
> dump_stack+0x71/0xab
> print_address_description+0x6a/0x280
> ? br_multicast_rcv+0x480c/0x4ad0 [bridge]
> __kasan_report+0x152/0x1aa
> ? br_multicast_rcv+0x480c/0x4ad0 [bridge]
> ? br_multicast_rcv+0x480c/0x4ad0 [bridge]
> kasan_report+0xe/0x20
> br_multicast_rcv+0x480c/0x4ad0 [bridge]
> ? br_multicast_disable_port+0x150/0x150 [bridge]
> ? ktime_get_with_offset+0xb4/0x150
> ? __kasan_kmalloc.constprop.6+0xa6/0xf0
> ? __netif_receive_skb+0x1b0/0x1b0
> ? br_fdb_update+0x10e/0x6e0 [bridge]
> ? br_handle_frame_finish+0x3c6/0x11d0 [bridge]
> br_handle_frame_finish+0x3c6/0x11d0 [bridge]
> ? br_pass_frame_up+0x3a0/0x3a0 [bridge]
> ? virtnet_probe+0x1c80/0x1c80 [virtio_net]
> br_handle_frame+0x731/0xd90 [bridge]
> ? select_idle_sibling+0x25/0x7d0
> ? br_handle_frame_finish+0x11d0/0x11d0 [bridge]
> __netif_receive_skb_core+0xced/0x2d70
> ? virtqueue_get_buf_ctx+0x230/0x1130 [virtio_ring]
> ? do_xdp_generic+0x20/0x20
> ? virtqueue_napi_complete+0x39/0x70 [virtio_net]
> ? virtnet_poll+0x94d/0xc78 [virtio_net]
> ? receive_buf+0x5120/0x5120 [virtio_net]
> ? __netif_receive_skb_one_core+0x97/0x1d0
> __netif_receive_skb_one_core+0x97/0x1d0
> ? __netif_receive_skb_core+0x2d70/0x2d70
> ? _raw_write_trylock+0x100/0x100
> ? __queue_work+0x41e/0xbe0
> process_backlog+0x19c/0x650
> ? _raw_read_lock_irq+0x40/0x40
> net_rx_action+0x71e/0xbc0
> ? __switch_to_asm+0x40/0x70
> ? napi_complete_done+0x360/0x360
> ? __switch_to_asm+0x34/0x70
> ? __switch_to_asm+0x40/0x70
> ? __schedule+0x85e/0x14d0
> __do_softirq+0x1db/0x5f9
> ? takeover_tasklets+0x5f0/0x5f0
> run_ksoftirqd+0x26/0x40
> smpboot_thread_fn+0x443/0x680
> ? sort_range+0x20/0x20
> ? schedule+0x94/0x210
> ? __kthread_parkme+0x78/0xf0
> ? sort_range+0x20/0x20
> kthread+0x2ae/0x3a0
> ? kthread_create_worker_on_cpu+0xc0/0xc0
> ret_from_fork+0x35/0x40
>
>The buggy address belongs to the page:
>page:ffffea0001084c00 refcount:0 mapcount:-128 mapping:0000000000000000
>index:0x0
>flags: 0xffffc000000000()
>raw: 00ffffc000000000 ffffea0000cfca08 ffffea0001098608
>0000000000000000
>raw: 0000000000000000 0000000000000003 00000000ffffff7f
>0000000000000000
>page dumped because: kasan: bad access detected
>
>Memory state around the buggy address:
> ffff888042130180: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> ffff888042130200: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>>ffff888042130280: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>                                     ^
> ffff888042130300: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> ffff888042130380: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>==================================================================
>Disabling lock debugging due to kernel taint


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