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

Commit Message

Shigeru Yoshida Dec. 1, 2024, 3:27 p.m. UTC

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().

[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

Fixes: be3d72a2896c ("bpf: move user_size out of bpf_test_init")
Reported-by: syzkaller <[e-mail]>
Signed-off-by: Shigeru Yoshida <[e-mail]>
---
 net/bpf/test_run.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Alexander Potapenko Dec. 2, 2024, 9:32 a.m. UTC | #1

On Sun, Dec 1, 2024 at 4:27 PM Shigeru Yoshida <[e-mail]> wrote:
>
> 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().

Hi Shigeru,

Thanks for taking care of this!

Am I understanding right that this bug was reported by your own
syzkaller instance?

Otherwise, if the report originates from syzkaller.appspot.com, could
you please append the bug hash to the Reported-by: tag?

Patch

diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
index 501ec4249fed..756250aa890f 100644
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -663,7 +663,7 @@  static void *bpf_test_init(const union bpf_attr *kattr, u32 user_size,
 	if (size < ETH_HLEN || size > PAGE_SIZE - headroom - tailroom)
 		return ERR_PTR(-EINVAL);
 
-	if (user_size > size)
+	if (user_size < ETH_HLEN || user_size > size)
 		return ERR_PTR(-EMSGSIZE);
 
 	size = SKB_DATA_ALIGN(size);