Merge branch 'prog_test_run-improvement'

Lorenz Bauer says:

====================
Right now, there is no safe way to use BPF_PROG_TEST_RUN with data_out.
This is because bpf_test_finish copies the output buffer to user space
without checking its size. This can lead to the kernel overwriting
data in user space after the buffer if xdp_adjust_head and friends are
in play.

Thanks to everyone for their advice and patience with this patch set!

Changes in v5:
* Fix up libbpf.map

Changes in v4:
* Document bpf_prog_test_run and bpf_prog_test_run_xattr
* Use struct bpf_prog_test_run_attr for return values

Changes in v3:
* Introduce bpf_prog_test_run_xattr instead of modifying the existing
  function

Changes in v2:
* Make the syscall return ENOSPC if data_size_out is too small
* Make bpf_prog_test_run return EINVAL if size_out is missing
* Document the new behaviour of data_size_out
====================
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

include/uapi/linux/bpf.h

@@ -374,8 +374,11 @@ union bpf_attr {
 	struct { /* anonymous struct used by BPF_PROG_TEST_RUN command */
 		__u32		prog_fd;
 		__u32		retval;
-		__u32		data_size_in;
-		__u32		data_size_out;
+		__u32		data_size_in;	/* input: len of data_in */
+		__u32		data_size_out;	/* input/output: len of data_out
+						 *   returns ENOSPC if data_out
+						 *   is too small.
+						 */
 		__aligned_u64	data_in;
 		__aligned_u64	data_out;
 		__u32		repeat;

net/bpf/test_run.c

@@ -74,8 +74,18 @@ static int bpf_test_finish(const union bpf_attr *kattr,
 {
 	void __user *data_out = u64_to_user_ptr(kattr->test.data_out);
 	int err = -EFAULT;
+	u32 copy_size = size;
 
-	if (data_out && copy_to_user(data_out, data, size))
+	/* Clamp copy if the user has provided a size hint, but copy the full
+	 * buffer if not to retain old behaviour.
+	 */
+	if (kattr->test.data_size_out &&
+	    copy_size > kattr->test.data_size_out) {
+		copy_size = kattr->test.data_size_out;
+		err = -ENOSPC;
+	}
+
+	if (data_out && copy_to_user(data_out, data, copy_size))
 		goto out;
 	if (copy_to_user(&uattr->test.data_size_out, &size, sizeof(size)))
 		goto out;
@@ -83,6 +93,7 @@ static int bpf_test_finish(const union bpf_attr *kattr,
 		goto out;
 	if (copy_to_user(&uattr->test.duration, &duration, sizeof(duration)))
 		goto out;
+	if (err != -ENOSPC)
 		err = 0;
 out:
 	return err;

tools/include/uapi/linux/bpf.h

@@ -374,8 +374,11 @@ union bpf_attr {
 	struct { /* anonymous struct used by BPF_PROG_TEST_RUN command */
 		__u32		prog_fd;
 		__u32		retval;
-		__u32		data_size_in;
-		__u32		data_size_out;
+		__u32		data_size_in;	/* input: len of data_in */
+		__u32		data_size_out;	/* input/output: len of data_out
+						 *   returns ENOSPC if data_out
+						 *   is too small.
+						 */
 		__aligned_u64	data_in;
 		__aligned_u64	data_out;
 		__u32		repeat;

tools/lib/bpf/bpf.c

@@ -463,6 +463,29 @@ int bpf_prog_test_run(int prog_fd, int repeat, void *data, __u32 size,
 	return ret;
 }
 
+int bpf_prog_test_run_xattr(struct bpf_prog_test_run_attr *test_attr)
+{
+	union bpf_attr attr;
+	int ret;
+
+	if (!test_attr->data_out && test_attr->data_size_out > 0)
+		return -EINVAL;
+
+	bzero(&attr, sizeof(attr));
+	attr.test.prog_fd = test_attr->prog_fd;
+	attr.test.data_in = ptr_to_u64(test_attr->data_in);
+	attr.test.data_out = ptr_to_u64(test_attr->data_out);
+	attr.test.data_size_in = test_attr->data_size_in;
+	attr.test.data_size_out = test_attr->data_size_out;
+	attr.test.repeat = test_attr->repeat;
+
+	ret = sys_bpf(BPF_PROG_TEST_RUN, &attr, sizeof(attr));
+	test_attr->data_size_out = attr.test.data_size_out;
+	test_attr->retval = attr.test.retval;
+	test_attr->duration = attr.test.duration;
+	return ret;
+}
+
 int bpf_prog_get_next_id(__u32 start_id, __u32 *next_id)
 {
 	union bpf_attr attr;

tools/lib/bpf/bpf.h

@@ -118,6 +118,25 @@ LIBBPF_API int bpf_prog_attach(int prog_fd, int attachable_fd,
 LIBBPF_API int bpf_prog_detach(int attachable_fd, enum bpf_attach_type type);
 LIBBPF_API int bpf_prog_detach2(int prog_fd, int attachable_fd,
 				enum bpf_attach_type type);
+
+struct bpf_prog_test_run_attr {
+	int prog_fd;
+	int repeat;
+	const void *data_in;
+	__u32 data_size_in;
+	void *data_out;      /* optional */
+	__u32 data_size_out; /* in: max length of data_out
+			      * out: length of data_out */
+	__u32 retval;        /* out: return code of the BPF program */
+	__u32 duration;      /* out: average per repetition in ns */
+};
+
+LIBBPF_API int bpf_prog_test_run_xattr(struct bpf_prog_test_run_attr *test_attr);
+
+/*
+ * bpf_prog_test_run does not check that data_out is large enough. Consider
+ * using bpf_prog_test_run_xattr instead.
+ */
 LIBBPF_API int bpf_prog_test_run(int prog_fd, int repeat, void *data,
 				 __u32 size, void *data_out, __u32 *size_out,
 				 __u32 *retval, __u32 *duration);

tools/lib/bpf/libbpf.map

@@ -65,6 +65,7 @@ LIBBPF_0.0.1 {
 		bpf_prog_load_xattr;
 		bpf_prog_query;
 		bpf_prog_test_run;
+		bpf_prog_test_run_xattr;
 		bpf_program__fd;
 		bpf_program__is_kprobe;
 		bpf_program__is_perf_event;

tools/testing/selftests/bpf/test_progs.c

@@ -70,7 +70,7 @@ static struct {
 	.tcp.urg_ptr = 123,
 };
 
-#define CHECK(condition, tag, format...) ({				\
+#define _CHECK(condition, tag, duration, format...) ({			\
 	int __ret = !!(condition);					\
 	if (__ret) {							\
 		error_cnt++;						\
@@ -83,6 +83,11 @@ static struct {
 	__ret;								\
 })
 
+#define CHECK(condition, tag, format...) \
+	_CHECK(condition, tag, duration, format)
+#define CHECK_ATTR(condition, tag, format...) \
+	_CHECK(condition, tag, tattr.duration, format)
+
 static int bpf_find_map(const char *test, struct bpf_object *obj,
 			const char *name)
 {
@@ -124,6 +129,53 @@ static void test_pkt_access(void)
 	bpf_object__close(obj);
 }
 
+static void test_prog_run_xattr(void)
+{
+	const char *file = "./test_pkt_access.o";
+	struct bpf_object *obj;
+	char buf[10];
+	int err;
+	struct bpf_prog_test_run_attr tattr = {
+		.repeat = 1,
+		.data_in = &pkt_v4,
+		.data_size_in = sizeof(pkt_v4),
+		.data_out = buf,
+		.data_size_out = 5,
+	};
+
+	err = bpf_prog_load(file, BPF_PROG_TYPE_SCHED_CLS, &obj,
+			    &tattr.prog_fd);
+	if (CHECK_ATTR(err, "load", "err %d errno %d\n", err, errno))
+		return;
+
+	memset(buf, 0, sizeof(buf));
+
+	err = bpf_prog_test_run_xattr(&tattr);
+	CHECK_ATTR(err != -1 || errno != ENOSPC || tattr.retval, "run",
+	      "err %d errno %d retval %d\n", err, errno, tattr.retval);
+
+	CHECK_ATTR(tattr.data_size_out != sizeof(pkt_v4), "data_size_out",
+	      "incorrect output size, want %lu have %u\n",
+	      sizeof(pkt_v4), tattr.data_size_out);
+
+	CHECK_ATTR(buf[5] != 0, "overflow",
+	      "BPF_PROG_TEST_RUN ignored size hint\n");
+
+	tattr.data_out = NULL;
+	tattr.data_size_out = 0;
+	errno = 0;
+
+	err = bpf_prog_test_run_xattr(&tattr);
+	CHECK_ATTR(err || errno || tattr.retval, "run_no_output",
+	      "err %d errno %d retval %d\n", err, errno, tattr.retval);
+
+	tattr.data_size_out = 1;
+	err = bpf_prog_test_run_xattr(&tattr);
+	CHECK_ATTR(err != -EINVAL, "run_wrong_size_out", "err %d\n", err);
+
+	bpf_object__close(obj);
+}
+
 static void test_xdp(void)
 {
 	struct vip key4 = {.protocol = 6, .family = AF_INET};
@@ -1837,6 +1889,7 @@ int main(void)
 	jit_enabled = is_jit_enabled();
 
 	test_pkt_access();
+	test_prog_run_xattr();
 	test_xdp();
 	test_xdp_adjust_tail();
 	test_l4lb_all();