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    Subject[PATCH AUTOSEL 4.20 089/105] bpf: don't assume build-id length is always 20 bytes
    Date
    From: Stanislav Fomichev <sdf@google.com>

    [ Upstream commit 0b698005a9d11c0e91141ec11a2c4918a129f703 ]

    Build-id length is not fixed to 20, it can be (`man ld` /--build-id):
    * 128-bit (uuid)
    * 160-bit (sha1)
    * any length specified in ld --build-id=0xhexstring

    To fix the issue of missing BPF_STACK_BUILD_ID_VALID for shorter build-ids,
    assume that build-id is somewhere in the range of 1 .. 20.
    Set the remaining bytes to zero.

    v2:
    * don't introduce new "len = min(BPF_BUILD_ID_SIZE, nhdr->n_descsz)",
    we already know that nhdr->n_descsz <= BPF_BUILD_ID_SIZE if we enter
    this 'if' condition

    Fixes: 615755a77b24 ("bpf: extend stackmap to save binary_build_id+offset instead of address")
    Acked-by: Song Liu <songliubraving@fb.com>
    Signed-off-by: Stanislav Fomichev <sdf@google.com>
    Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    kernel/bpf/stackmap.c | 7 +++++--
    1 file changed, 5 insertions(+), 2 deletions(-)

    diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
    index d9e2483669d0..f9df545e92f6 100644
    --- a/kernel/bpf/stackmap.c
    +++ b/kernel/bpf/stackmap.c
    @@ -180,11 +180,14 @@ static inline int stack_map_parse_build_id(void *page_addr,

    if (nhdr->n_type == BPF_BUILD_ID &&
    nhdr->n_namesz == sizeof("GNU") &&
    - nhdr->n_descsz == BPF_BUILD_ID_SIZE) {
    + nhdr->n_descsz > 0 &&
    + nhdr->n_descsz <= BPF_BUILD_ID_SIZE) {
    memcpy(build_id,
    note_start + note_offs +
    ALIGN(sizeof("GNU"), 4) + sizeof(Elf32_Nhdr),
    - BPF_BUILD_ID_SIZE);
    + nhdr->n_descsz);
    + memset(build_id + nhdr->n_descsz, 0,
    + BPF_BUILD_ID_SIZE - nhdr->n_descsz);
    return 0;
    }
    new_offs = note_offs + sizeof(Elf32_Nhdr) +
    --
    2.19.1
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