bonding: do not assume skb mac_header is set
CVE: CVE-2023-53601
Component: kernel
CWE: CWE-665
Severity: Moderate
CVSS v3: 5.6/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Release date: 2023-01-01T00:00:00+00:00

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

bonding: do not assume skb mac_header is set

Drivers must not assume in their ndo_start_xmit() that
skbs have their mac_header set. skb->data is all what is needed.

bonding seems to be one of the last offender as caught by syzbot:

WARNING: CPU: 1 PID: 12155 at include/linux/skbuff.h:2907 skb_mac_offset include/linux/skbuff.h:2913 [inline]
WARNING: CPU: 1 PID: 12155 at include/linux/skbuff.h:2907 bond_xmit_hash drivers/net/bonding/bond_main.c:4170 [inline]
WARNING: CPU: 1 PID: 12155 at include/linux/skbuff.h:2907 bond_xmit_3ad_xor_slave_get drivers/net/bonding/bond_main.c:5149 [inline]
WARNING: CPU: 1 PID: 12155 at include/linux/skbuff.h:2907 bond_3ad_xor_xmit drivers/net/bonding/bond_main.c:5186 [inline]
WARNING: CPU: 1 PID: 12155 at include/linux/skbuff.h:2907 __bond_start_xmit drivers/net/bonding/bond_main.c:5442 [inline]
WARNING: CPU: 1 PID: 12155 at include/linux/skbuff.h:2907 bond_start_xmit+0x14ab/0x19d0 drivers/net/bonding/bond_main.c:5470
Modules linked in:
CPU: 1 PID: 12155 Comm: syz-executor.3 Not tainted 6.1.30-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/25/2023
RIP: 0010:skb_mac_header include/linux/skbuff.h:2907 [inline]
RIP: 0010:skb_mac_offset include/linux/skbuff.h:2913 [inline]
RIP: 0010:bond_xmit_hash drivers/net/bonding/bond_main.c:4170 [inline]
RIP: 0010:bond_xmit_3ad_xor_slave_get drivers/net/bonding/bond_main.c:5149 [inline]
RIP: 0010:bond_3ad_xor_xmit drivers/net/bonding/bond_main.c:5186 [inline]
RIP: 0010:__bond_start_xmit drivers/net/bonding/bond_main.c:5442 [inline]
RIP: 0010:bond_start_xmit+0x14ab/0x19d0 drivers/net/bonding/bond_main.c:5470
Code: 8b 7c 24 30 e8 76 dd 1a 01 48 85 c0 74 0d 48 89 c3 e8 29 67 2e fe e9 15 ef ff ff e8 1f 67 2e fe e9 10 ef ff ff e8 15 67 2e fe <0f> 0b e9 45 f8 ff ff e8 09 67 2e fe e9 dc fa ff ff e8 ff 66 2e fe
RSP: 0018:ffffc90002fff6e0 EFLAGS: 00010283
RAX: ffffffff835874db RBX: 000000000000ffff RCX: 0000000000040000
RDX: ffffc90004dcf000 RSI: 00000000000000b5 RDI: 00000000000000b6
RBP: ffffc90002fff8b8 R08: ffffffff83586d16 R09: ffffffff83586584
R10: 0000000000000007 R11: ffff8881599fc780 R12: ffff88811b6a7b7e
R13: 1ffff110236d4f6f R14: ffff88811b6a7ac0 R15: 1ffff110236d4f76
FS: 00007f2e9eb47700(0000) GS:ffff8881f6b00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b2e421000 CR3: 000000010e6d4000 CR4: 00000000003526e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
[<ffffffff8471a49f>] netdev_start_xmit include/linux/netdevice.h:4925 [inline]
[<ffffffff8471a49f>] __dev_direct_xmit+0x4ef/0x850 net/core/dev.c:4380
[<ffffffff851d845b>] dev_direct_xmit include/linux/netdevice.h:3043 [inline]
[<ffffffff851d845b>] packet_direct_xmit+0x18b/0x300 net/packet/af_packet.c:284
[<ffffffff851c7472>] packet_snd net/packet/af_packet.c:3112 [inline]
[<ffffffff851c7472>] packet_sendmsg+0x4a22/0x64d0 net/packet/af_packet.c:3143
[<ffffffff8467a4b2>] sock_sendmsg_nosec net/socket.c:716 [inline]
[<ffffffff8467a4b2>] sock_sendmsg net/socket.c:736 [inline]
[<ffffffff8467a4b2>] __sys_sendto+0x472/0x5f0 net/socket.c:2139
[<ffffffff8467a715>] __do_sys_sendto net/socket.c:2151 [inline]
[<ffffffff8467a715>] __se_sys_sendto net/socket.c:2147 [inline]
[<ffffffff8467a715>] __x64_sys_sendto+0xe5/0x100 net/socket.c:2147
[<ffffffff8553071f>] do_syscall_x64 arch/x86/entry/common.c:50 [inline]
[<ffffffff8553071f>] do_syscall_64+0x2f/0x50 arch/x86/entry/common.c:80
[<ffffffff85600087>] entry_SYSCALL_64_after_hwframe+0x63/0xcd

Statement: The bonding driver incorrectly assumed skb->mac_header was always set and called skb_mac_offset(), which syzbot flagged with a WARN. Exploitation is limited to systems with bonding enabled and requires the ability to transmit via the bond device (PR:L), making the impact primarily a local DoS of the TX path.

Remediation: