CVE-2025-21925

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

llc: do not use skb_get() before dev_queue_xmit()

syzbot is able to crash hosts [1], using llc and devices

not supporting IFF_TX_SKB_SHARING.

In this case, e1000 driver calls eth_skb_pad(), while

the skb is shared.

Simply replace skb_get() by skb_clone() in net/llc/llc_s_ac.c

Note that e1000 driver might have an issue with pktgen,

because it does not clear IFF_TX_SKB_SHARING, this is an

orthogonal change.

We need to audit other skb_get() uses in net/llc.

[1]

kernel BUG at net/core/skbuff.c:2178 !

Oops: invalid opcode: 0000 [#1] PREEMPT SMP KASAN NOPTI

CPU: 0 UID: 0 PID: 16371 Comm: syz.2.2764 Not tainted 6.14.0-rc4-syzkaller-00052-gac9c34d1e45a #0

Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014

RIP: 0010:pskb_expand_head+0x6ce/0x1240 net/core/skbuff.c:2178

Call Trace:

<TASK>

__skb_pad+0x18a/0x610 net/core/skbuff.c:2466

__skb_put_padto include/linux/skbuff.h:3843 [inline]

skb_put_padto include/linux/skbuff.h:3862 [inline]

eth_skb_pad include/linux/etherdevice.h:656 [inline]

e1000_xmit_frame+0x2d99/0x5800 drivers/net/ethernet/intel/e1000/e1000_main.c:3128

__netdev_start_xmit include/linux/netdevice.h:5151 [inline]

netdev_start_xmit include/linux/netdevice.h:5160 [inline]

xmit_one net/core/dev.c:3806 [inline]

dev_hard_start_xmit+0x9a/0x7b0 net/core/dev.c:3822

sch_direct_xmit+0x1ae/0xc30 net/sched/sch_generic.c:343

__dev_xmit_skb net/core/dev.c:4045 [inline]

__dev_queue_xmit+0x13d4/0x43e0 net/core/dev.c:4621

dev_queue_xmit include/linux/netdevice.h:3313 [inline]

llc_sap_action_send_test_c+0x268/0x320 net/llc/llc_s_ac.c:144

llc_exec_sap_trans_actions net/llc/llc_sap.c:153 [inline]

llc_sap_next_state net/llc/llc_sap.c:182 [inline]

llc_sap_state_process+0x239/0x510 net/llc/llc_sap.c:209

llc_ui_sendmsg+0xd0d/0x14e0 net/llc/af_llc.c:993

sock_sendmsg_nosec net/socket.c:718 [inline]