CVE-2024-26635

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().

Lets 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

Affected Software

References

• https://git.kernel.org/stable/c/165ad1e22779685c3ed3dd349c6c4c632309cc62
• https://git.kernel.org/stable/c/660c3053d992b68fee893a0e9ec9159228cffdc6
• https://git.kernel.org/stable/c/9ccdef19cf9497c2803b005369668feb91cacdfd
• https://git.kernel.org/stable/c/b8e8838f82f332ae80c643dbb1ca4418d0628097
• https://git.kernel.org/stable/c/c0fe2fe7a5a291dfcf6dc64301732c8d3dc6a828
• https://git.kernel.org/stable/c/df57fc2f2abf548aa889a36ab0bdcc94a75399dc
• https://git.kernel.org/stable/c/e3f9bed9bee261e3347131764e42aeedf1ffea61
• https://git.kernel.org/stable/c/f1f34a515fb1e25e85dee94f781e7869ae351fb8