libbpf: Fix null-pointer dereference in find_prog_by_sec_insn()

maillist inclusion
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I5WLXN
CVE: CVE-2022-3606

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/tools/lib/bpf/libbpf.c?h=next-20221024&id=d0d382f95a9270dcf803539d6781d6bd67e3f5b2



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When there are no program sections, obj->programs is left unallocated,
and find_prog_by_sec_insn()'s search lands on &obj->programs[0] == NULL,
and will cause null-pointer dereference in the following access to
prog->sec_idx.

Guard the search with obj->nr_programs similar to what's being done in
__bpf_program__iter() to prevent null-pointer access from happening.

Fixes: db2b8b06 ("libbpf: Support CO-RE relocations for multi-prog sections")
Signed-off-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20221012022353.7350-4-shung-hsi.yu@suse.com


Signed-off-by: Pu Lehui <pulehui@huawei.com>
Reviewed-by: Kuohai Xu <xukuohai@huawei.com>
Reviewed-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>