On 12/02, Shigeru Yoshida 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().
>
> 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 <syzkaller@xxxxxxxxxxxxxxxx>
> Signed-off-by: Shigeru Yoshida <syoshida@xxxxxxxxxx>
> ---
> net/bpf/test_run.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> 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);
> --
> 2.47.0
>
I wonder whether 'size < ETH_HLEN' above is needed after your patch.
Feels like 'user_size < ETH_HLEN' supersedes it.
Acked-by: Stanislav Fomichev <sdf@xxxxxxxxxxx>
