CVE-2026-43456: bonding: fix type confusion in bond_setup_by_slave()

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

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

bonding: fix type confusion in bond_setup_by_slave()

kernel BUG at net/core/skbuff.c:2306!
Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI
RIP: 0010:pskb_expand_head+0xa08/0xfe0 net/core/skbuff.c:2306
RSP: 0018:ffffc90004aff760 EFLAGS: 00010293
RAX: 0000000000000000 RBX: ffff88807e3c8780 RCX: ffffffff89593e0e
RDX: ffff88807b7c4900 RSI: ffffffff89594747 RDI: ffff88807b7c4900
RBP: 0000000000000820 R08: 0000000000000005 R09: 0000000000000000
R10: 00000000961a63e0 R11: 0000000000000000 R12: ffff88807e3c8780
R13: 00000000961a6560 R14: dffffc0000000000 R15: 00000000961a63e0
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fe1a0ed8df0 CR3: 000000002d816000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 ipgre_header+0xdd/0x540 net/ipv4/ip_gre.c:900
 dev_hard_header include/linux/netdevice.h:3439 [inline]
 packet_snd net/packet/af_packet.c:3028 [inline]
 packet_sendmsg+0x3ae5/0x53c0 net/packet/af_packet.c:3108
 sock_sendmsg_nosec net/socket.c:727 [inline]
 __sock_sendmsg net/socket.c:742 [inline]
 ____sys_sendmsg+0xa54/0xc30 net/socket.c:2592
 ___sys_sendmsg+0x190/0x1e0 net/socket.c:2646
 __sys_sendmsg+0x170/0x220 net/socket.c:2678
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fe1a0e6c1a9

When a non-Ethernet device (e.g. GRE tunnel) is enslaved to a bond,
bond_setup_by_slave() directly copies the slave's header_ops to the
bond device:

    bond_dev->header_ops = slave_dev->header_ops;

This causes a type confusion when dev_hard_header() is later called
on the bond device. Functions like ipgre_header(), ip6gre_header(),all use
netdev_priv(dev) to access their device-specific private data. When
called with the bond device, netdev_priv() returns the bond's private
data (struct bonding) instead of the expected type (e.g. struct
ip_tunnel), leading to garbage values being read and kernel crashes.

Fix this by introducing bond_header_ops with wrapper functions that
delegate to the active slave's header_ops using the slave's own
device. This ensures netdev_priv() in the slave's header functions
always receives the correct device.

The fix is placed in the bonding driver rather than individual device
drivers, as the root cause is bond blindly inheriting header_ops from
the slave without considering that these callbacks expect a specific
netdev_priv() layout.

The type confusion can be observed by adding a printk in
ipgre_header() and running the following commands:

    ip link add dummy0 type dummy
    ip addr add 10.0.0.1/24 dev dummy0
    ip link set dummy0 up
    ip link add gre1 type gre local 10.0.0.1
    ip link add bond1 type bond mode active-backup
    ip link set gre1 master bond1
    ip link set gre1 up
    ip link set bond1 up
    ip addr add fe80::1/64 dev bond1

The Linux kernel CVE team has assigned CVE-2026-43456 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 2.6.24 with commit 1284cd3a2b740d0118458d2ea470a1e5bc19b187 and fixed in 6.12.78 with commit 9baf26a91565b7bb2b1d9f99aaf884a2b28c2f6d
	Issue introduced in 2.6.24 with commit 1284cd3a2b740d0118458d2ea470a1e5bc19b187 and fixed in 6.18.19 with commit 6ac890f1d60ac3707ee8dae15a67d9a833e49956
	Issue introduced in 2.6.24 with commit 1284cd3a2b740d0118458d2ea470a1e5bc19b187 and fixed in 6.19.9 with commit 95597d11dc8bddb2b9a051c9232000bfbb5e43ba
	Issue introduced in 2.6.24 with commit 1284cd3a2b740d0118458d2ea470a1e5bc19b187 and fixed in 7.0 with commit 950803f7254721c1c15858fbbfae3deaaeeecb11

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-43456
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	drivers/net/bonding/bond_main.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/9baf26a91565b7bb2b1d9f99aaf884a2b28c2f6d
	https://git.kernel.org/stable/c/6ac890f1d60ac3707ee8dae15a67d9a833e49956
	https://git.kernel.org/stable/c/95597d11dc8bddb2b9a051c9232000bfbb5e43ba
	https://git.kernel.org/stable/c/950803f7254721c1c15858fbbfae3deaaeeecb11