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    Subject[PATCH 5.13 041/104] bpf: Fix OOB read when printing XDP link fdinfo
    Date
    From: Lorenz Bauer <lmb@cloudflare.com>

    [ Upstream commit d6371c76e20d7d3f61b05fd67b596af4d14a8886 ]

    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>
    Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
    Link: https://lore.kernel.org/bpf/20210719085134.43325-2-lmb@cloudflare.com
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    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 f883f01a5061..def596a85752 100644
    --- a/include/linux/bpf_types.h
    +++ b/include/linux/bpf_types.h
    @@ -132,4 +132,5 @@ BPF_LINK_TYPE(BPF_LINK_TYPE_CGROUP, cgroup)
    BPF_LINK_TYPE(BPF_LINK_TYPE_ITER, iter)
    #ifdef CONFIG_NET
    BPF_LINK_TYPE(BPF_LINK_TYPE_NETNS, netns)
    +BPF_LINK_TYPE(BPF_LINK_TYPE_XDP, xdp)
    #endif
    --
    2.30.2


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