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    SubjectRe: [PATCH net] ipv6: mcast: fix data-race in ipv6_mc_down / mld_ifc_work
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    On 1/18/24 02:21, Nikita Zhandarovich wrote:

    Hi Nikita,
    Thanks a lot for this work!

    > idev->mc_ifc_count can be written over without proper locking.
    >
    > Originally found by syzbot [1], fix this issue by encapsulating calls
    > to mld_ifc_stop_work() (and mld_gq_stop_work() for good measure) with
    > mutex_lock() and mutex_unlock() accordingly as these functions
    > should only be called with mc_lock per their declarations.
    >
    > [1]
    > 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
    > ...
    >
    > 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
    > ...
    >
    > Fixes: 2d9a93b4902b ("mld: convert from timer to delayed work")
    > Reported-by: syzbot+a9400cabb1d784e49abf@syzkaller.appspotmail.com
    > Link:
    https://lore.kernel.org/all/000000000000994e09060ebcdffb@google.com/
    > Signed-off-by: Nikita Zhandarovich <n.zhandarovich@fintech.ru>
    > ---
    > net/ipv6/mcast.c | 4 ++++
    > 1 file changed, 4 insertions(+)
    >
    > diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c
    > index b75d3c9d41bb..bc6e0a0bad3c 100644
    > --- a/net/ipv6/mcast.c
    > +++ b/net/ipv6/mcast.c
    > @@ -2722,8 +2722,12 @@ void ipv6_mc_down(struct inet6_dev *idev)
    > synchronize_net();
    > mld_query_stop_work(idev);
    > mld_report_stop_work(idev);
    > +
    > + mutex_lock(&idev->mc_lock);
    > mld_ifc_stop_work(idev);
    > mld_gq_stop_work(idev);
    > + mutex_unlock(&idev->mc_lock);
    > +
    > mld_dad_stop_work(idev);
    > }


    Acked-by: Taehee Yoo <ap420073@gmail.com>

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