[PATCH bpf-next 2/2] selftests/bpf: Add tests for iter next method returning valid pointer

[Juntong Deng]

This patch adds two test cases for iter next method returning valid
pointer, which can also used as usage examples.

Currently iter next method should return valid pointer.

iter_next_trusted is the correct usage and test if iter next method
return valid pointer. bpf_iter_task_vma_next has KF_RET_NULL flag,
so the returned pointer may be NULL. We need to check if the pointer
is NULL before using it.

iter_next_trusted_or_null is the incorrect usage. There is no checking
before using the pointer, so it will be rejected by the verifier.

Signed-off-by: Juntong Deng <juntong.deng@xxxxxxxxxxx>
---
 .../selftests/bpf/bpf_testmod/bpf_testmod.c   |  5 ++
 .../bpf/bpf_testmod/bpf_testmod_kfunc.h       |  2 +
 .../testing/selftests/bpf/prog_tests/iters.c  |  5 +-
 .../selftests/bpf/progs/iters_testmod.c       | 48 +++++++++++++++++++
 4 files changed, 59 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/bpf/progs/iters_testmod.c

diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
index a80b0d2c6f38..810d8005211e 100644
--- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
+++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
@@ -176,6 +176,10 @@ __bpf_kfunc void bpf_kfunc_dynptr_test(struct bpf_dynptr *ptr,
 {
 }
 
+__bpf_kfunc void bpf_kfunc_valid_pointer_test(struct vm_area_struct *ptr)
+{
+}
+
 __bpf_kfunc struct bpf_testmod_ctx *
 bpf_testmod_ctx_create(int *err)
 {
@@ -533,6 +537,7 @@ BTF_ID_FLAGS(func, bpf_iter_testmod_seq_next, KF_ITER_NEXT | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_iter_testmod_seq_destroy, KF_ITER_DESTROY)
 BTF_ID_FLAGS(func, bpf_kfunc_common_test)
 BTF_ID_FLAGS(func, bpf_kfunc_dynptr_test)
+BTF_ID_FLAGS(func, bpf_kfunc_valid_pointer_test, KF_TRUSTED_ARGS)
 BTF_ID_FLAGS(func, bpf_testmod_ctx_create, KF_ACQUIRE | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_testmod_ctx_release, KF_RELEASE)
 BTF_KFUNCS_END(bpf_testmod_common_kfunc_ids)
diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod_kfunc.h b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod_kfunc.h
index e587a79f2239..8f122dc8a328 100644
--- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod_kfunc.h
+++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod_kfunc.h
@@ -144,4 +144,6 @@ void bpf_kfunc_dynptr_test(struct bpf_dynptr *ptr, struct bpf_dynptr *ptr__nulla
 struct bpf_testmod_ctx *bpf_testmod_ctx_create(int *err) __ksym;
 void bpf_testmod_ctx_release(struct bpf_testmod_ctx *ctx) __ksym;
 
+void bpf_kfunc_valid_pointer_test(struct vm_area_struct *ptr) __ksym;
+
 #endif /* _BPF_TESTMOD_KFUNC_H */
diff --git a/tools/testing/selftests/bpf/prog_tests/iters.c b/tools/testing/selftests/bpf/prog_tests/iters.c
index 3c440370c1f0..89ff23c4a8bc 100644
--- a/tools/testing/selftests/bpf/prog_tests/iters.c
+++ b/tools/testing/selftests/bpf/prog_tests/iters.c
@@ -14,6 +14,7 @@
 #include "iters_state_safety.skel.h"
 #include "iters_looping.skel.h"
 #include "iters_num.skel.h"
+#include "iters_testmod.skel.h"
 #include "iters_testmod_seq.skel.h"
 #include "iters_task_vma.skel.h"
 #include "iters_task.skel.h"
@@ -297,8 +298,10 @@ void test_iters(void)
 	RUN_TESTS(iters);
 	RUN_TESTS(iters_css_task);
 
-	if (env.has_testmod)
+	if (env.has_testmod) {
+		RUN_TESTS(iters_testmod);
 		RUN_TESTS(iters_testmod_seq);
+	}
 
 	if (test__start_subtest("num"))
 		subtest_num_iters();
diff --git a/tools/testing/selftests/bpf/progs/iters_testmod.c b/tools/testing/selftests/bpf/progs/iters_testmod.c
new file mode 100644
index 000000000000..009b9f7ad45c
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/iters_testmod.c
@@ -0,0 +1,48 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "vmlinux.h"
+#include "bpf_experimental.h"
+#include <bpf/bpf_helpers.h>
+#include "bpf_misc.h"
+#include "../bpf_testmod/bpf_testmod_kfunc.h"
+
+char _license[] SEC("license") = "GPL";
+
+SEC("raw_tp/sys_enter")
+__success
+int iter_next_trusted(const void *ctx)
+{
+	struct task_struct *task = bpf_get_current_task_btf();
+	struct bpf_iter_task_vma vma_it;
+	struct vm_area_struct *vma;
+
+	bpf_iter_task_vma_new(&vma_it, task, 0);
+
+	vma = bpf_iter_task_vma_next(&vma_it);
+
+	if (vma == NULL)
+		goto out;
+
+	bpf_kfunc_valid_pointer_test(vma);
+out:
+	bpf_iter_task_vma_destroy(&vma_it);
+	return 0;
+}
+
+SEC("raw_tp/sys_enter")
+__failure __msg("Possibly NULL pointer passed to trusted arg0")
+int iter_next_trusted_or_null(const void *ctx)
+{
+	struct task_struct *task = bpf_get_current_task_btf();
+	struct bpf_iter_task_vma vma_it;
+	struct vm_area_struct *vma;
+
+	bpf_iter_task_vma_new(&vma_it, task, 0);
+
+	vma = bpf_iter_task_vma_next(&vma_it);
+
+	bpf_kfunc_valid_pointer_test(vma);
+
+	bpf_iter_task_vma_destroy(&vma_it);
+	return 0;
+}
-- 
2.39.2