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    Subject[PATCH 5.17 0436/1126] libbpf: Fix possible NULL pointer dereference when destroying skeleton
    Date
    From: Yafang Shao <laoar.shao@gmail.com>

    [ Upstream commit a32ea51a3f17ce6524c9fc19d311e708331c8b5f ]

    When I checked the code in skeleton header file generated with my own
    bpf prog, I found there may be possible NULL pointer dereference when
    destroying skeleton. Then I checked the in-tree bpf progs, finding that is
    a common issue. Let's take the generated samples/bpf/xdp_redirect_cpu.skel.h
    for example. Below is the generated code in
    xdp_redirect_cpu__create_skeleton():

    xdp_redirect_cpu__create_skeleton
    struct bpf_object_skeleton *s;
    s = (struct bpf_object_skeleton *)calloc(1, sizeof(*s));
    if (!s)
    goto error;
    ...
    error:
    bpf_object__destroy_skeleton(s);
    return -ENOMEM;

    After goto error, the NULL 's' will be deferenced in
    bpf_object__destroy_skeleton().

    We can simply fix this issue by just adding a NULL check in
    bpf_object__destroy_skeleton().

    Fixes: d66562fba1ce ("libbpf: Add BPF object skeleton support")
    Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
    Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
    Link: https://lore.kernel.org/bpf/20220108134739.32541-1-laoar.shao@gmail.com
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    tools/lib/bpf/libbpf.c | 3 +++
    1 file changed, 3 insertions(+)

    diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
    index 7f10dd501a52..fdb3536afa7d 100644
    --- a/tools/lib/bpf/libbpf.c
    +++ b/tools/lib/bpf/libbpf.c
    @@ -11795,6 +11795,9 @@ void bpf_object__detach_skeleton(struct bpf_object_skeleton *s)

    void bpf_object__destroy_skeleton(struct bpf_object_skeleton *s)
    {
    + if (!s)
    + return;
    +
    if (s->progs)
    bpf_object__detach_skeleton(s);
    if (s->obj)
    --
    2.34.1


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