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Medium severity5.5NVD Advisory· Published Jan 31, 2025· Updated May 12, 2026

CVE-2025-21678

CVE-2025-21678

Description

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

gtp: Destroy device along with udp socket's netns dismantle.

gtp_newlink() links the device to a list in dev_net(dev) instead of src_net, where a udp tunnel socket is created.

Even when src_net is removed, the device stays alive on dev_net(dev). Then, removing src_net triggers the splat below. [0]

In this example, gtp0 is created in ns2, and the udp socket is created in ns1.

ip netns add ns1 ip netns add ns2 ip -n ns1 link add netns ns2 name gtp0 type gtp role sgsn ip netns del ns1

Let's link the device to the socket's netns instead.

Now, gtp_net_exit_batch_rtnl() needs another netdev iteration to remove all gtp devices in the netns.

[0]: ref_tracker: net notrefcnt@000000003d6e7d05 has 1/2 users at sk_alloc (./include/net/net_namespace.h:345 net/core/sock.c:2236) inet_create (net/ipv4/af_inet.c:326 net/ipv4/af_inet.c:252) __sock_create (net/socket.c:1558) udp_sock_create4 (net/ipv4/udp_tunnel_core.c:18) gtp_create_sock (./include/net/udp_tunnel.h:59 drivers/net/gtp.c:1423) gtp_create_sockets (drivers/net/gtp.c:1447) gtp_newlink (drivers/net/gtp.c:1507) rtnl_newlink (net/core/rtnetlink.c:3786 net/core/rtnetlink.c:3897 net/core/rtnetlink.c:4012) rtnetlink_rcv_msg (net/core/rtnetlink.c:6922) netlink_rcv_skb (net/netlink/af_netlink.c:2542) netlink_unicast (net/netlink/af_netlink.c:1321 net/netlink/af_netlink.c:1347) netlink_sendmsg (net/netlink/af_netlink.c:1891) ____sys_sendmsg (net/socket.c:711 net/socket.c:726 net/socket.c:2583) ___sys_sendmsg (net/socket.c:2639) __sys_sendmsg (net/socket.c:2669) do_syscall_64 (arch/x86/entry/common.c:52 arch/x86/entry/common.c:83)

WARNING: CPU: 1 PID: 60 at lib/ref_tracker.c:179 ref_tracker_dir_exit (lib/ref_tracker.c:179) Modules linked in: CPU: 1 UID: 0 PID: 60 Comm: kworker/u16:2 Not tainted 6.13.0-rc5-00147-g4c1224501e9d #5 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014 Workqueue: netns cleanup_net RIP: 0010:ref_tracker_dir_exit (lib/ref_tracker.c:179) Code: 00 00 00 fc ff df 4d 8b 26 49 bd 00 01 00 00 00 00 ad de 4c 39 f5 0f 85 df 00 00 00 48 8b 74 24 08 48 89 df e8 a5 cc 12 02 90 <0f> 0b 90 48 8d 6b 44 be 04 00 00 00 48 89 ef e8 80 de 67 ff 48 89 RSP: 0018:ff11000009a07b60 EFLAGS: 00010286 RAX: 0000000000002bd3 RBX: ff1100000f4e1aa0 RCX: 1ffffffff0e40ac6 RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffff8423ee3c RBP: ff1100000f4e1af0 R08: 0000000000000001 R09: fffffbfff0e395ae R10: 0000000000000001 R11: 0000000000036001 R12: ff1100000f4e1af0 R13: dead000000000100 R14: ff1100000f4e1af0 R15: dffffc0000000000 FS: 0000000000000000(0000) GS:ff1100006ce80000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f9b2464bd98 CR3: 0000000005286005 CR4: 0000000000771ef0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe07f0 DR7: 0000000000000400 PKRU: 55555554 Call Trace:

? __warn (kernel/panic.c:748) ? ref_tracker_dir_exit (lib/ref_tracker.c:179) ? report_bug (lib/bug.c:201 lib/bug.c:219) ? handle_bug (arch/x86/kernel/traps.c:285) ? exc_invalid_op (arch/x86/kernel/traps.c:309 (discriminator 1)) ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:621) ? _raw_spin_unlock_irqrestore (./arch/x86/include/asm/irqflags.h:42 ./arch/x86/include/asm/irqflags.h:97 ./arch/x86/include/asm/irqflags.h:155 ./include/linux/spinlock_api_smp.h:151 kernel/locking/spinlock.c:194) ? ref_tracker_dir_exit (lib/ref_tracker.c:179) ? __pfx_ref_tracker_dir_exit (lib/ref_tracker.c:158) ? kfree (mm/slub.c:4613 mm/slub.c:4761) net_free (net/core/net_namespace.c:476 net/core/net_namespace.c:467) cleanup_net (net/core/net_namespace.c:664 (discriminator 3)) process_one_work (kernel/workqueue.c:3229) worker_thread (kernel/workqueue.c:3304 kernel/workqueue.c:3391 ---truncated---

AI Insight

LLM-synthesized narrative grounded in this CVE's description and references.

Linux kernel GTP driver fails to clean up devices when the UDP socket's network namespace is removed, leading to a use-after-free warning.

The Linux kernel GTP (GPRS Tunneling Protocol) driver contained a network namespace (netns) management flaw. In gtp_newlink(), the GTP device was linked to a list in dev_net(dev), while the UDP tunnel socket was created in a potentially different namespace (src_net). When src_net was removed, the socket's reference to the network namespace was released, but the device remained in dev_net(dev). This mismatch caused a refcount tracker warning when the socket tried to access the already-dismantled network namespace [1] [description].

Exploitation requires creating a GTP device in one network namespace (ns2) with the underlying UDP socket created in another namespace (ns1), and then deleting the socket's namespace (ns1). No special privileges beyond CAP_NET_ADMIN are likely required to trigger the condition. The kernel then warns about a reference tracking inconsistency, as shown in the syzkaller-like report [description].

The impact is a kernel warning and potential use-after-free condition when the device attempts to access the socket's network namespace after it has been freed. This can lead to system instability or denial of service. The CVSS v3 base score is 5.5 (Medium) [1].

The fix (commit efec287cb9) updates gtp_newlink() to link the device to the socket's network namespace, ensuring proper lifecycle coupling. The gtp_net_exit_batch_rtnl() function was also adjusted to iterate over all GTP devices in the namespace during teardown [4]. Siemens has listed this CVE as affecting SIMATIC S7-1500 TM MFP - GNU/Linux subsystem (all versions) [1], though the primary fix is in the upstream Linux kernel.

References
  1. SSA-265688
  2. Making sure you're not a bot!

AI Insight generated on May 20, 2026. Synthesized from this CVE's description and the cited reference URLs; citations are validated against the source bundle.

Affected products

79

Patches

0

No patches discovered yet.

Vulnerability mechanics

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References

11

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