libbpf: Fix logic for finding matching program for CO-RE relocation

Fix the bug in bpf_object__relocate_core() which can lead to finding
invalid matching BPF program when processing CO-RE relocation. IF
matching program is not found, last encountered program will be assumed
to be correct program and thus error detection won't detect the problem.

Fixes: 9c82a63c ("libbpf: Fix CO-RE relocs against .text section")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220426004511.2691730-4-andrii@kernel.org

tools/lib/bpf/libbpf.c

@@ -5677,9 +5677,10 @@ bpf_object__relocate_core(struct bpf_object *obj, const char *targ_btf_path)
 		 */
 		prog = NULL;
 		for (i = 0; i < obj->nr_programs; i++) {
-			prog = &obj->programs[i];
-			if (strcmp(prog->sec_name, sec_name) == 0)
+			if (strcmp(obj->programs[i].sec_name, sec_name) == 0) {
+				prog = &obj->programs[i];
 				break;
+			}
 		}
 		if (!prog) {
 			pr_warn("sec '%s': failed to find a BPF program\n", sec_name);