CVE-2022-48785

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

ipv6: mcast: use rcu-safe version of ipv6_get_lladdr()

Some time ago 8965779d2c0e ("ipv6,mcast: always hold idev->lock before mca_lock")

switched ipv6_get_lladdr() to __ipv6_get_lladdr(), which is rcu-unsafe

version. That was OK, because idev->lock was held for these codepaths.

In 88e2ca308094 ("mld: convert ifmcaddr6 to RCU") these external locks were

removed, so we probably need to restore the original rcu-safe call.

Otherwise, we occasionally get a machine crashed/stalled with the following

in dmesg:

[ 3405.966610][T230589] general protection fault, probably for non-canonical address 0xdead00000000008c: 0000 [#1] SMP NOPTI

[ 3405.982083][T230589] CPU: 44 PID: 230589 Comm: kworker/44:3 Tainted: G O 5.15.19-cloudflare-2022.2.1 #1

[ 3405.998061][T230589] Hardware name: SUPA-COOL-SERV

[ 3406.009552][T230589] Workqueue: mld mld_ifc_work

[ 3406.017224][T230589] RIP: 0010:__ipv6_get_lladdr+0x34/0x60

[ 3406.025780][T230589] Code: 57 10 48 83 c7 08 48 89 e5 48 39 d7 74 3e 48 8d 82 38 ff ff ff eb 13 48 8b 90 d0 00 00 00 48 8d 82 38 ff ff ff 48 39 d7 74 22 <66> 83 78 32 20 77 1b 75 e4 89 ca 23 50 2c 75 dd 48 8b 50 08 48 8b

[ 3406.055748][T230589] RSP: 0018:ffff94e4b3fc3d10 EFLAGS: 00010202

[ 3406.065617][T230589] RAX: dead00000000005a RBX: ffff94e4b3fc3d30 RCX: 0000000000000040

[ 3406.077477][T230589] RDX: dead000000000122 RSI: ffff94e4b3fc3d30 RDI: ffff8c3a31431008

[ 3406.089389][T230589] RBP: ffff94e4b3fc3d10 R08: 0000000000000000 R09: 0000000000000000

[ 3406.101445][T230589] R10: ffff8c3a31430000 R11: 000000000000000b R12: ffff8c2c37887100

[ 3406.113553][T230589] R13: ffff8c3a39537000 R14: 00000000000005dc R15: ffff8c3a31431000

[ 3406.125730][T230589] FS: 0000000000000000(0000) GS:ffff8c3b9fc80000(0000) knlGS:0000000000000000

[ 3406.138992][T230589] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

[ 3406.149895][T230589] CR2: 00007f0dfea1db60 CR3: 000000387b5f2000 CR4: 0000000000350ee0

[ 3406.162421][T230589] Call Trace:

[ 3406.170235][T230589] <TASK>

[ 3406.177736][T230589] mld_newpack+0xfe/0x1a0

[ 3406.186686][T230589] add_grhead+0x87/0xa0

[ 3406.195498][T230589] add_grec+0x485/0x4e0

[ 3406.204310][T230589] ? newidle_balance+0x126/0x3f0

[ 3406.214024][T230589] mld_ifc_work+0x15d/0x450

[ 3406.223279][T230589] process_one_work+0x1e6/0x380

[ 3406.232982][T230589] worker_thread+0x50/0x3a0

[ 3406.242371][T230589] ? rescuer_thread+0x360/0x360

[ 3406.252175][T230589] kthread+0x127/0x150

[ 3406.261197][T230589] ? set_kthread_struct+0x40/0x40

[ 3406.271287][T230589] ret_from_fork+0x22/0x30

[ 3406.280812][T230589] </TASK>

[ 3406.288937][T230589] Modules linked in: ... [last unloaded: kheaders]

[ 3406.476714][T230589] ---[ end trace 3525a7655f2f3b9e ]---