Merge branch 'fix-missing-process_iter_arg-type-check'

Kumar Kartikeya Dwivedi says:

====================
Fix missing process_iter_arg type check

I am taking over Tao's earlier patch set that can be found at [0], after
an offline discussion. The bug reported in that thread is that
process_iter_arg missed a reg->type == PTR_TO_STACK check. Fix this by
adding it in, and also address comments from Andrii on the earlier
attempt. Include more selftests to ensure the error is caught.

  [0]: https://lore.kernel.org/bpf/20241107214736.347630-1-tao.lyu@epfl.ch

Changelog:
----------
v1 -> v2:
v1: https://lore.kernel.org/bpf/20241127230147.4158201-1-memxor@gmail.com
====================

Link: https://patch.msgid.link/20241203000238.3602922-1-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/verifier.c

@@ -8189,6 +8189,11 @@ static int process_iter_arg(struct bpf_verifier_env *env, int regno, int insn_id
 	const struct btf_type *t;
 	int spi, err, i, nr_slots, btf_id;
 
+	if (reg->type != PTR_TO_STACK) {
+		verbose(env, "arg#%d expected pointer to an iterator on stack\n", regno - 1);
+		return -EINVAL;
+	}
+
 	/* For iter_{new,next,destroy} functions, btf_check_iter_kfuncs()
 	 * ensures struct convention, so we wouldn't need to do any BTF
 	 * validation here. But given iter state can be passed as a parameter

tools/testing/selftests/bpf/progs/iters.c

@@ -1486,4 +1486,30 @@ int iter_subprog_check_stacksafe(const void *ctx)
 	return 0;
 }
 
+struct bpf_iter_num global_it;
+
+SEC("raw_tp")
+__failure __msg("arg#0 expected pointer to an iterator on stack")
+int iter_new_bad_arg(const void *ctx)
+{
+	bpf_iter_num_new(&global_it, 0, 1);
+	return 0;
+}
+
+SEC("raw_tp")
+__failure __msg("arg#0 expected pointer to an iterator on stack")
+int iter_next_bad_arg(const void *ctx)
+{
+	bpf_iter_num_next(&global_it);
+	return 0;
+}
+
+SEC("raw_tp")
+__failure __msg("arg#0 expected pointer to an iterator on stack")
+int iter_destroy_bad_arg(const void *ctx)
+{
+	bpf_iter_num_destroy(&global_it);
+	return 0;
+}
+
 char _license[] SEC("license") = "GPL";

tools/testing/selftests/bpf/progs/verifier_bits_iter.c

@@ -35,9 +35,9 @@ __description("uninitialized iter in ->next()")
 __failure __msg("expected an initialized iter_bits as arg #1")
 int BPF_PROG(next_uninit, struct bpf_iter_meta *meta, struct cgroup *cgrp)
 {
-	struct bpf_iter_bits *it = NULL;
+	struct bpf_iter_bits it = {};
 
-	bpf_iter_bits_next(it);
+	bpf_iter_bits_next(&it);
 	return 0;
 }