CVE-2025-21867

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

bpf, test_run: Fix use-after-free issue in eth_skb_pkt_type()

KMSAN reported a use-after-free issue in eth_skb_pkt_type()[1]. The

cause of the issue was that eth_skb_pkt_type() accessed skb's data

that didn't contain an Ethernet header. This occurs when

bpf_prog_test_run_xdp() passes an invalid value as the user_data

argument to bpf_test_init().

Fix this by returning an error when user_data is less than ETH_HLEN in

bpf_test_init(). Additionally, remove the check for "if (user_size >

size)" as it is unnecessary.

[1]

BUG: KMSAN: use-after-free in eth_skb_pkt_type include/linux/etherdevice.h:627 [inline]

BUG: KMSAN: use-after-free in eth_type_trans+0x4ee/0x980 net/ethernet/eth.c:165

eth_skb_pkt_type include/linux/etherdevice.h:627 [inline]

eth_type_trans+0x4ee/0x980 net/ethernet/eth.c:165

__xdp_build_skb_from_frame+0x5a8/0xa50 net/core/xdp.c:635

xdp_recv_frames net/bpf/test_run.c:272 [inline]

xdp_test_run_batch net/bpf/test_run.c:361 [inline]

bpf_test_run_xdp_live+0x2954/0x3330 net/bpf/test_run.c:390

bpf_prog_test_run_xdp+0x148e/0x1b10 net/bpf/test_run.c:1318

bpf_prog_test_run+0x5b7/0xa30 kernel/bpf/syscall.c:4371

__sys_bpf+0x6a6/0xe20 kernel/bpf/syscall.c:5777

__do_sys_bpf kernel/bpf/syscall.c:5866 [inline]

__se_sys_bpf kernel/bpf/syscall.c:5864 [inline]

__x64_sys_bpf+0xa4/0xf0 kernel/bpf/syscall.c:5864

x64_sys_call+0x2ea0/0x3d90 arch/x86/include/generated/asm/syscalls_64.h:322

do_syscall_x64 arch/x86/entry/common.c:52 [inline]

do_syscall_64+0xd9/0x1d0 arch/x86/entry/common.c:83

entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was created at:

free_pages_prepare mm/page_alloc.c:1056 [inline]

free_unref_page+0x156/0x1320 mm/page_alloc.c:2657

__free_pages+0xa3/0x1b0 mm/page_alloc.c:4838

bpf_ringbuf_free kernel/bpf/ringbuf.c:226 [inline]

ringbuf_map_free+0xff/0x1e0 kernel/bpf/ringbuf.c:235

bpf_map_free kernel/bpf/syscall.c:838 [inline]

bpf_map_free_deferred+0x17c/0x310 kernel/bpf/syscall.c:862

process_one_work kernel/workqueue.c:3229 [inline]

process_scheduled_works+0xa2b/0x1b60 kernel/workqueue.c:3310

worker_thread+0xedf/0x1550 kernel/workqueue.c:3391

kthread+0x535/0x6b0 kernel/kthread.c:389

ret_from_fork+0x6e/0x90 arch/x86/kernel/process.c:147

ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

CPU: 1 UID: 0 PID: 17276 Comm: syz.1.16450 Not tainted 6.12.0-05490-g9bb88c659673 #8

Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-3.fc41 04/01/2014