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

llc: Drop support for ETH_P_TR_802_2.

syzbot reported an uninit-value bug below. [0]

llc supports ETH_P_802_2 (0x0004) and used to support ETH_P_TR_802_2
(0x0011), and syzbot abused the latter to trigger the bug.

write$tun(r0, &(0x7f0000000040)={@val={0x0, 0x11}, @val, @mpls={[], @llc={@snap={0xaa, 0x1, ‘)’, “90e5dd”}}}}, 0x16)

llc_conn_handler() initialises local variables {saddr,daddr}.mac
based on skb in llc_pdu_decode_sa()/llc_pdu_decode_da() and passes
them to __llc_lookup().

However, the initialisation is done only when skb->protocol is
htons(ETH_P_802_2), otherwise, __llc_lookup_established() and
__llc_lookup_listener() will read garbage.

The missing initialisation existed prior to commit 211ed865108e
(“net: delete all instances of special processing for token ring”).

It removed the part to kick out the token ring stuff but forgot to
close the door allowing ETH_P_TR_802_2 packets to sneak into llc_rcv().

Let’s remove llc_tr_packet_type and complete the deprecation.

[0]:
BUG: KMSAN: uninit-value in __llc_lookup_established+0xe9d/0xf90
__llc_lookup_established+0xe9d/0xf90
__llc_lookup net/llc/llc_conn.c:611 [inline]
llc_conn_handler+0x4bd/0x1360 net/llc/llc_conn.c:791
llc_rcv+0xfbb/0x14a0 net/llc/llc_input.c:206
__netif_receive_skb_one_core net/core/dev.c:5527 [inline]
__netif_receive_skb+0x1a6/0x5a0 net/core/dev.c:5641
netif_receive_skb_internal net/core/dev.c:5727 [inline]
netif_receive_skb+0x58/0x660 net/core/dev.c:5786
tun_rx_batched+0x3ee/0x980 drivers/net/tun.c:1555
tun_get_user+0x53af/0x66d0 drivers/net/tun.c:2002
tun_chr_write_iter+0x3af/0x5d0 drivers/net/tun.c:2048
call_write_iter include/linux/fs.h:2020 [inline]
new_sync_write fs/read_write.c:491 [inline]
vfs_write+0x8ef/0x1490 fs/read_write.c:584
ksys_write+0x20f/0x4c0 fs/read_write.c:637
__do_sys_write fs/read_write.c:649 [inline]
__se_sys_write fs/read_write.c:646 [inline]
__x64_sys_write+0x93/0xd0 fs/read_write.c:646
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
entry_SYSCALL_64_after_hwframe+0x63/0x6b

Local variable daddr created at:
llc_conn_handler+0x53/0x1360 net/llc/llc_conn.c:783
llc_rcv+0xfbb/0x14a0 net/llc/llc_input.c:206

CPU: 1 PID: 5004 Comm: syz-executor994 Not tainted 6.6.0-syzkaller-14500-g1c41041124bd #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/09/2023