[Bridge] KMSAN: uninit-value in br_mdb_ip_get

Dmitry Vyukov dvyukov at google.com
Fri May 31 11:28:41 UTC 2019 

On Thu, Feb 21, 2019 at 11:56 AM Dmitry Vyukov <dvyukov at google.com> wrote:
>
> On Mon, Jan 28, 2019 at 8:13 PM syzbot
> <syzbot+8dfe5ee27aa6d2e396c2 at syzkaller.appspotmail.com> wrote:
> >
> > Hello,
> >
> > syzbot found the following crash on:
> >
> > HEAD commit:    02f2d5aea531 kmsan: (presumably) fix dma_map_page_attrs()
> > git tree:       kmsan
> > console output: https://syzkaller.appspot.com/x/log.txt?x=173a7310c00000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=52c9737ec5618f82
> > dashboard link: https://syzkaller.appspot.com/bug?extid=8dfe5ee27aa6d2e396c2
> > compiler:       clang version 8.0.0 (trunk 350509)
> >
> > Unfortunately, I don't have any reproducer for this crash yet.
> >
> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > Reported-by: syzbot+8dfe5ee27aa6d2e396c2 at syzkaller.appspotmail.com
>
>
> There is also a use-after-free reported at around the same stack:
> https://groups.google.com/forum/#!topic/syzkaller-bugs/8V7VqxxTEzc
> The question is: can these reports be related? One is root cause of another?
>
>
> > ==================================================================
> > BUG: KMSAN: uninit-value in __rhashtable_lookup
> > include/linux/rhashtable.h:505 [inline]
> > BUG: KMSAN: uninit-value in rhashtable_lookup
> > include/linux/rhashtable.h:534 [inline]
> > BUG: KMSAN: uninit-value in br_mdb_ip_get+0x52b/0x740
> > net/bridge/br_multicast.c:97
> > CPU: 0 PID: 11379 Comm: udevd Not tainted 5.0.0-rc1+ #7
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> > Google 01/01/2011
> > Call Trace:
> >   <IRQ>
> >   __dump_stack lib/dump_stack.c:77 [inline]
> >   dump_stack+0x173/0x1d0 lib/dump_stack.c:113
> >   kmsan_report+0x12e/0x2a0 mm/kmsan/kmsan.c:600
> >   __msan_warning+0x82/0xf0 mm/kmsan/kmsan_instr.c:313
> >   __rhashtable_lookup include/linux/rhashtable.h:505 [inline]
> >   rhashtable_lookup include/linux/rhashtable.h:534 [inline]
> >   br_mdb_ip_get+0x52b/0x740 net/bridge/br_multicast.c:97
> >   br_multicast_new_group+0xa7/0x1640 net/bridge/br_multicast.c:467
> >   br_multicast_add_group+0x242/0xf00 net/bridge/br_multicast.c:552
> >   br_ip4_multicast_add_group net/bridge/br_multicast.c:606 [inline]
> >   br_ip4_multicast_igmp3_report net/bridge/br_multicast.c:972 [inline]
> >   br_multicast_ipv4_rcv net/bridge/br_multicast.c:1615 [inline]
> >   br_multicast_rcv+0x3a88/0x6560 net/bridge/br_multicast.c:1701
> >   br_dev_xmit+0xbc5/0x16a0 net/bridge/br_device.c:93
> >   __netdev_start_xmit include/linux/netdevice.h:4382 [inline]
> >   netdev_start_xmit include/linux/netdevice.h:4391 [inline]
> >   xmit_one net/core/dev.c:3278 [inline]
> >   dev_hard_start_xmit+0x604/0xc40 net/core/dev.c:3294
> >   __dev_queue_xmit+0x2e48/0x3b80 net/core/dev.c:3864
> >   dev_queue_xmit+0x4b/0x60 net/core/dev.c:3897
> >   neigh_hh_output include/net/neighbour.h:498 [inline]
> >   neigh_output include/net/neighbour.h:506 [inline]
> >   ip_finish_output2+0x156d/0x1820 net/ipv4/ip_output.c:229
> >   ip_finish_output+0xd2b/0xfd0 net/ipv4/ip_output.c:317
> >   NF_HOOK_COND include/linux/netfilter.h:278 [inline]
> >   ip_output+0x53f/0x610 net/ipv4/ip_output.c:405
> >   dst_output include/net/dst.h:444 [inline]
> >   ip_local_out+0x164/0x1d0 net/ipv4/ip_output.c:124
> >   igmpv3_sendpack net/ipv4/igmp.c:417 [inline]
> >   igmpv3_send_cr net/ipv4/igmp.c:705 [inline]
> >   igmp_ifc_timer_expire+0x12cb/0x1aa0 net/ipv4/igmp.c:793
> >   call_timer_fn+0x285/0x600 kernel/time/timer.c:1325
> >   expire_timers kernel/time/timer.c:1362 [inline]
> >   __run_timers+0xdb4/0x11d0 kernel/time/timer.c:1681
> >   run_timer_softirq+0x2e/0x50 kernel/time/timer.c:1694
> >   __do_softirq+0x53f/0x93a kernel/softirq.c:293
> >   invoke_softirq kernel/softirq.c:375 [inline]
> >   irq_exit+0x214/0x250 kernel/softirq.c:416
> >   exiting_irq+0xe/0x10 arch/x86/include/asm/apic.h:536
> >   smp_apic_timer_interrupt+0x48/0x70 arch/x86/kernel/apic/apic.c:1064
> >   apic_timer_interrupt+0x2e/0x40 arch/x86/entry/entry_64.S:814
> >   </IRQ>
> > RIP: 0010:__msan_chain_origin+0x93/0xe0 mm/kmsan/kmsan_instr.c:201
> > Code: 89 f7 e8 f0 e0 ff ff 89 c3 65 ff 0c 25 04 90 03 00 65 8b 04 25 04 90
> > 03 00 85 c0 75 30 e8 f5 a2 3f ff 4c 89 7d d0 ff 75 d0 9d <65> 48 8b 04 25
> > 28 00 00 00 48 3b 45 e0 75 0d 89 d8 48 83 c4 18 5b
> > RSP: 0018:ffff8880a53cf6f0 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13
> > RAX: 0000000000000000 RBX: 00000000a06000af RCX: c7641d3373f0d000
> > RDX: 0000000000000003 RSI: 0000000000480020 RDI: 0000000085c0000c
> > RBP: ffff8880a53cf720 R08: 0000000000000003 R09: ffff8880a53cf4ac
> > R10: ffffffff8ae01788 R11: 0000000000000000 R12: ffff8880a53cfcd0
> > R13: ffff8880a53cfcc8 R14: 0000000085c0000c R15: 0000000000000246
> >   step_into+0x70c/0x1b90 fs/namei.c:1778
> >   walk_component+0x1d0/0xba0 fs/namei.c:1829
> >   link_path_walk+0xa9e/0x2160 fs/namei.c:2135
> >   path_openat+0x30e/0x6b90 fs/namei.c:3533
> >   do_filp_open+0x2b8/0x710 fs/namei.c:3564
> >   do_sys_open+0x642/0xa30 fs/open.c:1063
> >   __do_sys_open fs/open.c:1081 [inline]
> >   __se_sys_open+0xad/0xc0 fs/open.c:1076
> >   __x64_sys_open+0x4a/0x70 fs/open.c:1076
> >   do_syscall_64+0xbc/0xf0 arch/x86/entry/common.c:291
> >   entry_SYSCALL_64_after_hwframe+0x63/0xe7
> > RIP: 0033:0x7f4526cc5120
> > Code: 48 8b 15 1b 4d 2b 00 f7 d8 64 89 02 83 c8 ff c3 90 90 90 90 90 90 90
> > 90 90 90 83 3d d5 a4 2b 00 00 75 10 b8 02 00 00 00 0f 05 <48> 3d 01 f0 ff
> > ff 73 31 c3 48 83 ec 08 e8 5e 8c 01 00 48 89 04 24
> > RSP: 002b:00007ffdb010be48 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
> > RAX: ffffffffffffffda RBX: 0000000000ee2fd0 RCX: 00007f4526cc5120
> > RDX: 00000000000001b6 RSI: 0000000000080000 RDI: 00007ffdb010bf20
> > RBP: 00007ffdb010bec0 R08: 0000000000000008 R09: 0000000000000001
> > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000008
> > R13: 000000000041f57a R14: 0000000000ed3250 R15: 000000000000000b
> >
> > Local variable description: ----br_group.i.i at br_multicast_rcv
> > Variable was created at:
> >   br_multicast_rcv+0x1e7/0x6560 net/bridge/br_multicast.c:1690
> >   br_dev_xmit+0xbc5/0x16a0 net/bridge/br_device.c:93
> > ==================================================================


Nikolay seems to fix this with the following commit:

commit 1515a63fc413f160d20574ab0894e7f1020c7be2
Author: Nikolay Aleksandrov
Date:   Wed Apr 3 23:27:24 2019 +0300
    net: bridge: always clear mcast matching struct on reports and leaves

Let's close the bug:

#syz fix:
net: bridge: always clear mcast matching struct on reports and leaves

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