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

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

bonding: fix type confusion in bondsetupbyslave()

kernel BUG at net/core/skbuff.c:2306! Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI RIP: 0010:pskbexpandhead+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> ipgreheader+0xdd/0x540 net/ipv4/ipgre.c:900 devhardheader include/linux/netdevice.h:3439 [inline] packetsnd net/packet/afpacket.c:3028 [inline] packetsendmsg+0x3ae5/0x53c0 net/packet/afpacket.c:3108 socksendmsgnosec net/socket.c:727 [inline] socksendmsg net/socket.c:742 [inline] syssendmsg+0xa54/0xc30 net/socket.c:2592 syssendmsg+0x190/0x1e0 net/socket.c:2646 syssendmsg+0x170/0x220 net/socket.c:2678 dosyscallx64 arch/x86/entry/syscall64.c:63 [inline] dosyscall64+0x106/0xf80 arch/x86/entry/syscall64.c:94 entrySYSCALL64afterhwframe+0x77/0x7f RIP: 0033:0x7fe1a0e6c1a9

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

bonddev->headerops = slavedev->headerops;

This causes a type confusion when devhardheader() is later called on the bond device. Functions like ipgreheader(), ip6greheader(),all use netdevpriv(dev) to access their device-specific private data. When called with the bond device, netdevpriv() returns the bond's private data (struct bonding) instead of the expected type (e.g. struct iptunnel), leading to garbage values being read and kernel crashes.

Fix this by introducing bondheaderops with wrapper functions that delegate to the active slave's headerops using the slave's own device. This ensures netdevpriv() 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 headerops from the slave without considering that these callbacks expect a specific netdevpriv() layout.

The type confusion can be observed by adding a printk in ipgreheader() 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