On Fri, Jul 16, 2021 at 3:05 AM Lorenz Bauer <lmb@xxxxxxxxxxxxxx> wrote:
>
> We got the following UBSAN report on one of our testing machines:
>
> ================================================================================
> UBSAN: array-index-out-of-bounds in kernel/bpf/syscall.c:2389:24
> index 6 is out of range for type 'char *[6]'
> CPU: 43 PID: 930921 Comm: systemd-coredum Tainted: G O 5.10.48-cloudflare-kasan-2021.7.0 #1
> Hardware name: <snip>
> Call Trace:
> dump_stack+0x7d/0xa3
> ubsan_epilogue+0x5/0x40
> __ubsan_handle_out_of_bounds.cold+0x43/0x48
> ? seq_printf+0x17d/0x250
> bpf_link_show_fdinfo+0x329/0x380
> ? bpf_map_value_size+0xe0/0xe0
> ? put_files_struct+0x20/0x2d0
> ? __kasan_kmalloc.constprop.0+0xc2/0xd0
> seq_show+0x3f7/0x540
> seq_read_iter+0x3f8/0x1040
> seq_read+0x329/0x500
> ? seq_read_iter+0x1040/0x1040
> ? __fsnotify_parent+0x80/0x820
> ? __fsnotify_update_child_dentry_flags+0x380/0x380
> vfs_read+0x123/0x460
> ksys_read+0xed/0x1c0
> ? __x64_sys_pwrite64+0x1f0/0x1f0
> do_syscall_64+0x33/0x40
> entry_SYSCALL_64_after_hwframe+0x44/0xa9
> <snip>
> ================================================================================
> ================================================================================
> UBSAN: object-size-mismatch in kernel/bpf/syscall.c:2384:2
>
> From the report, we can infer that some array access in bpf_link_show_fdinfo at index 6
> is out of bounds. The obvious candidate is bpf_link_type_strs[BPF_LINK_TYPE_XDP] with
> BPF_LINK_TYPE_XDP == 6. It turns out that BPF_LINK_TYPE_XDP is missing from bpf_types.h
> and therefore doesn't have an entry in bpf_link_type_strs:
>
> pos: 0
> flags: 02000000
> mnt_id: 13
> link_type: (null)
> link_id: 4
> prog_tag: bcf7977d3b93787c
> prog_id: 4
> ifindex: 1
>
> Fixes: aa8d3a716b59 ("bpf, xdp: Add bpf_link-based XDP attachment API")
> Signed-off-by: Lorenz Bauer <lmb@xxxxxxxxxxxxxx>
> ---
Well, oops. Thanks for the fix!
Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
It would be great to have a compilation error for something like this.
I wonder if we can do something to detect this going forward?
> include/linux/bpf_types.h | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/include/linux/bpf_types.h b/include/linux/bpf_types.h
> index a9db1eae6796..be95f2722ad9 100644
> --- a/include/linux/bpf_types.h
> +++ b/include/linux/bpf_types.h
> @@ -135,3 +135,4 @@ BPF_LINK_TYPE(BPF_LINK_TYPE_ITER, iter)
> #ifdef CONFIG_NET
> BPF_LINK_TYPE(BPF_LINK_TYPE_NETNS, netns)
> #endif
> +BPF_LINK_TYPE(BPF_LINK_TYPE_XDP, xdp)
> --
> 2.30.2
>
