On Fri, 16 Jul 2021 at 22:01, Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote:
>
> On 7/16/21 10:43 PM, Andrii Nakryiko wrote:
> > 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)
>
> Lorenz, does this compile when you don't have CONFIG_NET configured? I would assume
> this needs to go right below the netns one depending on CONFIG_NET.. at least the
> bpf_xdp_link_lops are in net/core/dev.c which is only built under CONFIG_NET.
It does compile, since the only use of the macro is to stringify a
link type for fdinfo. I'll move it into CONFIG_NET to be consistent
with netdev though.
--
Lorenz Bauer | Systems Engineer
6th Floor, County Hall/The Riverside Building, SE1 7PB, UK
www.cloudflare.com
