Re: [syzbot] [net?] KCSAN: data-race in ipv6_mc_down / mld_ifc_work (2)

[Eric Dumazet]

On Fri, Jan 12, 2024 at 11:10 AM syzbot
<syzbot+a9400cabb1d784e49abf@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    8735c7c84d1b Merge tag '6.7rc7-smb3-srv-fix' of git://git..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=17948c9ae80000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=4da1e2da456c3a7d
> dashboard link: https://syzkaller.appspot.com/bug?extid=a9400cabb1d784e49abf
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/f263d974af01/disk-8735c7c8.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/9faf34fc0b3e/vmlinux-8735c7c8.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/0b52a58ecd0e/bzImage-8735c7c8.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+a9400cabb1d784e49abf@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> ==================================================================
> BUG: KCSAN: data-race in ipv6_mc_down / mld_ifc_work
>
> write to 0xffff88813a80c832 of 1 bytes by task 3771 on cpu 0:
>  mld_ifc_stop_work net/ipv6/mcast.c:1080 [inline]
>  ipv6_mc_down+0x10a/0x280 net/ipv6/mcast.c:2725
>  addrconf_ifdown+0xe32/0xf10 net/ipv6/addrconf.c:3949
>  addrconf_notify+0x310/0x980
>  notifier_call_chain kernel/notifier.c:93 [inline]
>  raw_notifier_call_chain+0x6b/0x1c0 kernel/notifier.c:461
>  __dev_notify_flags+0x205/0x3d0
>  dev_change_flags+0xab/0xd0 net/core/dev.c:8685
>  do_setlink+0x9f6/0x2430 net/core/rtnetlink.c:2916
>  rtnl_group_changelink net/core/rtnetlink.c:3458 [inline]
>  __rtnl_newlink net/core/rtnetlink.c:3717 [inline]
>  rtnl_newlink+0xbb3/0x1670 net/core/rtnetlink.c:3754
>  rtnetlink_rcv_msg+0x807/0x8c0 net/core/rtnetlink.c:6558
>  netlink_rcv_skb+0x126/0x220 net/netlink/af_netlink.c:2545
>  rtnetlink_rcv+0x1c/0x20 net/core/rtnetlink.c:6576
>  netlink_unicast_kernel net/netlink/af_netlink.c:1342 [inline]
>  netlink_unicast+0x589/0x650 net/netlink/af_netlink.c:1368
>  netlink_sendmsg+0x66e/0x770 net/netlink/af_netlink.c:1910
>  sock_sendmsg_nosec net/socket.c:730 [inline]
>  __sock_sendmsg net/socket.c:745 [inline]
>  ____sys_sendmsg+0x37c/0x4d0 net/socket.c:2584
>  ___sys_sendmsg net/socket.c:2638 [inline]
>  __sys_sendmsg+0x1e9/0x270 net/socket.c:2667
>  __do_sys_sendmsg net/socket.c:2676 [inline]
>  __se_sys_sendmsg net/socket.c:2674 [inline]
>  __x64_sys_sendmsg+0x46/0x50 net/socket.c:2674
>  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>  do_syscall_64+0x44/0x110 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x63/0x6b
>
> write to 0xffff88813a80c832 of 1 bytes by task 22 on cpu 1:
>  mld_ifc_work+0x54c/0x7b0 net/ipv6/mcast.c:2653
>  process_one_work kernel/workqueue.c:2627 [inline]
>  process_scheduled_works+0x5b8/0xa30 kernel/workqueue.c:2700
>  worker_thread+0x525/0x730 kernel/workqueue.c:2781
>  kthread+0x1d7/0x210 kernel/kthread.c:388
>  ret_from_fork+0x48/0x60 arch/x86/kernel/process.c:147
>  ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242
>
> value changed: 0x02 -> 0x00
>
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 1 PID: 22 Comm: kworker/1:0 Not tainted 6.7.0-rc7-syzkaller-00029-g8735c7c84d1b #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
> Workqueue: mld mld_ifc_work
> ==================================================================
>
>
> ---
> This report 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@xxxxxxxxxxxxxxxx.
>
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
>
> If the report is already addressed, let syzbot know by replying with:
> #syz fix: exact-commit-title
>
> If you want to overwrite report's subsystems, reply with:
> #syz set subsystems: new-subsystem
> (See the list of subsystem names on the web dashboard)
>
> If the report is a duplicate of another one, reply with:
> #syz dup: exact-subject-of-another-report
>
> If you want to undo deduplication, reply with:
> #syz undup

Bug added in

commit 63ed8de4be81b699ca727e9f8e3344bd487806d7
Author: Taehee Yoo <ap420073@xxxxxxxxx>
Date:   Thu Mar 25 16:16:57 2021 +0000

    mld: add mc_lock for protecting per-interface mld data


ipv6_mc_down() calls mld_ifc_stop_work() while mc_lock is not held.