Messages in this thread | | | Subject | Re: [PATCH bpf] bpf: fix OOB read when printing XDP link fdinfo | From | Daniel Borkmann <> | Date | Fri, 16 Jul 2021 23:00:58 +0200 |
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On 7/16/21 10:43 PM, Andrii Nakryiko wrote: > On Fri, Jul 16, 2021 at 3:05 AM Lorenz Bauer <lmb@cloudflare.com> 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@cloudflare.com> >> --- > > Well, oops. Thanks for the fix! > > Acked-by: Andrii Nakryiko <andrii@kernel.org> > > 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.
Thanks, Daniel
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