linux-kernel - Re: [PATCH net] ipv6: mcast: fix data-race in ipv6_mc_down / mld_ifc

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Date: Thu, 18 Jan 2024 16:11:03 +0900
From: Taehee Yoo <ap420073@...il.com>
To: Nikita Zhandarovich <n.zhandarovich@...tech.ru>,
 "David S. Miller" <davem@...emloft.net>
Cc: David Ahern <dsahern@...nel.org>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 syzbot+a9400cabb1d784e49abf@...kaller.appspotmail.com
Subject: Re: [PATCH net] ipv6: mcast: fix data-race in ipv6_mc_down /
 mld_ifc_work



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@...kaller.appspotmail.com
 > Link: 
https://lore.kernel.org/all/000000000000994e09060ebcdffb@google.com/
 > Signed-off-by: Nikita Zhandarovich <n.zhandarovich@...tech.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@...il.com>