Re: KMSAN: uninit-value in br_mdb_ip_get

[Dmitry Vyukov]

On Mon, Jan 28, 2019 at 8:13 PM syzbot
<syzbot+8dfe5ee27aa6d2e396c2@xxxxxxxxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxxxxxxx


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@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
> ==================================================================
>
>
> ---
> This bug is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxxx
>
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> syzbot.
>
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