bpf: abort verification if env->cur_state->loop_entry != NULL

In addition to warning abort verification with -EFAULT.
If env->cur_state->loop_entry != NULL something is irrecoverably
buggy.

Fixes: bbbc02b7445e ("bpf: copy_verifier_state() should copy 'loop_entry' field")
Suggested-by: Andrii Nakryiko <[e-mail]>
Signed-off-by: Eduard Zingerman <[e-mail]>
Acked-by: Andrii Nakryiko <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

kernel/bpf/verifier.c

···
 						return err;
 					break;
 				} else {
-					if (WARN_ON_ONCE(env->cur_state->loop_entry))
-						env->cur_state->loop_entry = NULL;
+					if (WARN_ON_ONCE(env->cur_state->loop_entry)) {
+						verbose(env, "verifier bug: env->cur_state->loop_entry != NULL\n");
+						return -EFAULT;
+					}
 					do_print_state = true;
 					continue;
 				}