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

[syzbot]

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+a9400c...@syzkaller.appspotmail.com

==================================================================
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
==================================================================


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[Eric Dumazet]

Bug added in

commit 63ed8de4be81b699ca727e9f8e3344bd487806d7
Author: Taehee Yoo <ap42...@gmail.com>
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.

[Taehee Yoo]

On 1/12/24 21:01, Eric Dumazet wrote:

Hi Eric,
Thank you for the report!

Thanks a lot for the analysis, I will look into this.

Thanks a lot!
Taehee Yoo