CVE-2025-21867

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

bpf, testrun: Fix use-after-free issue in ethskbpkttype()

KMSAN reported a use-after-free issue in ethskbpkttype()[1]. The cause of the issue was that ethskbpkttype() accessed skb's data that didn't contain an Ethernet header. This occurs when bpfprogtestrunxdp() passes an invalid value as the userdata argument to bpftest_init().

Fix this by returning an error when userdata is less than ETHHLEN in bpftestinit(). Additionally, remove the check for "if (user_size > size)" as it is unnecessary.

[1] BUG: KMSAN: use-after-free in ethskbpkttype include/linux/etherdevice.h:627 [inline] BUG: KMSAN: use-after-free in ethtypetrans+0x4ee/0x980 net/ethernet/eth.c:165 ethskbpkttype include/linux/etherdevice.h:627 [inline] ethtypetrans+0x4ee/0x980 net/ethernet/eth.c:165 __xdpbuildskbfromframe+0x5a8/0xa50 net/core/xdp.c:635 xdprecvframes net/bpf/testrun.c:272 [inline] xdptestrunbatch net/bpf/testrun.c:361 [inline] bpftestrunxdplive+0x2954/0x3330 net/bpf/testrun.c:390 bpfprogtestrunxdp+0x148e/0x1b10 net/bpf/testrun.c:1318 bpfprogtestrun+0x5b7/0xa30 kernel/bpf/syscall.c:4371 __sys_bpf+0x6a6/0xe20 kernel/bpf/syscall.c:5777 __dosysbpf kernel/bpf/syscall.c:5866 [inline] __sesysbpf kernel/bpf/syscall.c:5864 [inline] _x64sysbpf+0xa4/0xf0 kernel/bpf/syscall.c:5864 x64syscall+0x2ea0/0x3d90 arch/x86/include/generated/asm/syscalls64.h:322 dosyscallx64 arch/x86/entry/common.c:52 [inline] dosyscall64+0xd9/0x1d0 arch/x86/entry/common.c:83 entrySYSCALL64afterhwframe+0x77/0x7f

Uninit was created at: freepagesprepare mm/pagealloc.c:1056 [inline] freeunrefpage+0x156/0x1320 mm/pagealloc.c:2657 __freepages+0xa3/0x1b0 mm/pagealloc.c:4838 bpfringbuffree kernel/bpf/ringbuf.c:226 [inline] ringbufmapfree+0xff/0x1e0 kernel/bpf/ringbuf.c:235 bpfmapfree kernel/bpf/syscall.c:838 [inline] bpfmapfreedeferred+0x17c/0x310 kernel/bpf/syscall.c:862 processonework kernel/workqueue.c:3229 [inline] processscheduledworks+0xa2b/0x1b60 kernel/workqueue.c:3310 workerthread+0xedf/0x1550 kernel/workqueue.c:3391 kthread+0x535/0x6b0 kernel/kthread.c:389 retfromfork+0x6e/0x90 arch/x86/kernel/process.c:147 retfromforkasm+0x1a/0x30 arch/x86/entry/entry64.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