CVE-2026-31419

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

net: bonding: fix use-after-free in bond_xmit_broadcast()

bond_xmit_broadcast() reuses the original skb for the last slave

(determined by bond_is_last_slave()) and clones it for others.

Concurrent slave enslave/release can mutate the slave list during

RCU-protected iteration, changing which slave is "last" mid-loop.

This causes the original skb to be double-consumed (double-freed).

Replace the racy bond_is_last_slave() check with a simple index

comparison (i + 1 == slaves_count) against the pre-snapshot slave

count taken via READ_ONCE() before the loop. This preserves the

zero-copy optimization for the last slave while making the "last"

determination stable against concurrent list mutations.

The UAF can trigger the following crash:

==================================================================

BUG: KASAN: slab-use-after-free in skb_clone

Read of size 8 at addr ffff888100ef8d40 by task exploit/147

CPU: 1 UID: 0 PID: 147 Comm: exploit Not tainted 7.0.0-rc3+ #4 PREEMPTLAZY

Call Trace:

<TASK>

dump_stack_lvl (lib/dump_stack.c:123)

print_report (mm/kasan/report.c:379 mm/kasan/report.c:482)

kasan_report (mm/kasan/report.c:597)

skb_clone (include/linux/skbuff.h:1724 include/linux/skbuff.h:1792 include/linux/skbuff.h:3396 net/core/skbuff.c:2108)

bond_xmit_broadcast (drivers/net/bonding/bond_main.c:5334)

bond_start_xmit (drivers/net/bonding/bond_main.c:5567 drivers/net/bonding/bond_main.c:5593)

dev_hard_start_xmit (include/linux/netdevice.h:5325 include/linux/netdevice.h:5334 net/core/dev.c:3871 net/core/dev.c:3887)

__dev_queue_xmit (include/linux/netdevice.h:3601 net/core/dev.c:4838)

ip6_finish_output2 (include/net/neighbour.h:540 include/net/neighbour.h:554 net/ipv6/ip6_output.c:136)

ip6_finish_output (net/ipv6/ip6_output.c:208 net/ipv6/ip6_output.c:219)

ip6_output (net/ipv6/ip6_output.c:250)

ip6_send_skb (net/ipv6/ip6_output.c:1985)

udp_v6_send_skb (net/ipv6/udp.c:1442)

udpv6_sendmsg (net/ipv6/udp.c:1733)

__sys_sendto (net/socket.c:730 net/socket.c:742 net/socket.c:2206)

__x64_sys_sendto (net/socket.c:2209)

do_syscall_64 (arch/x86/entry/syscall_64.c:63 arch/x86/entry/syscall_64.c:94)

entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)

</TASK>

Allocated by task 147:

Freed by task 147:

The buggy address belongs to the object at ffff888100ef8c80

which belongs to the cache skbuff_head_cache of size 224

The buggy address is located 192 bytes inside of

freed 224-byte region [ffff888100ef8c80, ffff888100ef8d60)

Memory state around the buggy address:

ffff888100ef8c00: fb fb fb fb fc fc fc fc fc fc fc fc fc fc fc fc

ffff888100ef8c80: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

>ffff888100ef8d00: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc

^

ffff888100ef8d80: fc fc fc fc fc fc fc fc fa fb fb fb fb fb fb fb

ffff888100ef8e00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

==================================================================