CVE-2024-26631

In the Linux kernel, the following vulnerability has been resolved:

ipv6: mcast: fix data-race in ipv6_mc_down / mld_ifc_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

...