[PATCH bpf-next 3/3] selftests/bpf: Test linux_binprm user memory kfuncs

[Anastasios Papagiannis]

This patch adds a sleepable BPF LSM program attached to
bprm_check_security to test bpf_copy_from_user_bprm() and
bpf_copy_from_user_bprm_str().

Starting at bprm->p, verify that bpf_copy_from_user_bprm() can copy the
contiguous NUL-separated argument data. Then use
bpf_copy_from_user_bprm_str() to read each argument separately,
by advancing the offset based on the returned length.

Signed-off-by: Anastasios Papagiannis <tasos.papagiannnis@xxxxxxxxx>
---
 .../bpf/prog_tests/copy_from_user_bprm.c      | 52 +++++++++++++
 .../selftests/bpf/progs/copy_from_user_bprm.c | 74 +++++++++++++++++++
 2 files changed, 126 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/copy_from_user_bprm.c
 create mode 100644 tools/testing/selftests/bpf/progs/copy_from_user_bprm.c

diff --git a/tools/testing/selftests/bpf/prog_tests/copy_from_user_bprm.c b/tools/testing/selftests/bpf/prog_tests/copy_from_user_bprm.c
new file mode 100644
index 000000000000..3d5080a3975e
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/copy_from_user_bprm.c
@@ -0,0 +1,52 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <errno.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include <test_progs.h>
+
+#include "copy_from_user_bprm.skel.h"
+
+void test_copy_from_user_bprm(void)
+{
+	struct copy_from_user_bprm *skel;
+	pid_t child;
+	int status;
+
+	skel = copy_from_user_bprm__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "open_and_load"))
+		return;
+
+	if (!ASSERT_OK(copy_from_user_bprm__attach(skel), "attach"))
+		goto out;
+
+	child = fork();
+	if (!ASSERT_GE(child, 0, "fork"))
+		goto out;
+
+	if (!child) {
+		char *const argv[] = { "first", "second-argument", NULL };
+
+		skel->bss->monitored_pid = getpid();
+		execv("/bin/true", argv);
+		_exit(errno);
+	}
+
+	if (!ASSERT_EQ(waitpid(child, &status, 0), child, "waitpid"))
+		goto out;
+
+	if (ASSERT_TRUE(WIFEXITED(status), "child_exited"))
+		ASSERT_EQ(WEXITSTATUS(status), EPERM, "exec_errno");
+
+	ASSERT_EQ(skel->bss->bprm_argc, 2, "bprm_argc");
+	ASSERT_EQ(skel->bss->invalid_flags_ret, -EINVAL, "invalid_flags_ret");
+	ASSERT_EQ(skel->bss->copy_ret, 0, "copy_ret");
+	ASSERT_EQ(skel->bss->str_arg0_ret, 6, "str_arg0_ret");
+	ASSERT_EQ(skel->bss->str_arg1_ret, 16, "str_arg1_ret");
+	ASSERT_EQ(skel->bss->args_match, 1, "args_match");
+	ASSERT_EQ(skel->bss->str_args_match, 1, "str_args_match");
+
+out:
+	copy_from_user_bprm__destroy(skel);
+}
diff --git a/tools/testing/selftests/bpf/progs/copy_from_user_bprm.c b/tools/testing/selftests/bpf/progs/copy_from_user_bprm.c
new file mode 100644
index 000000000000..679363811edc
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/copy_from_user_bprm.c
@@ -0,0 +1,74 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "vmlinux.h"
+
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include <errno.h>
+#include "bpf_misc.h"
+
+char _license[] SEC("license") = "GPL";
+
+static const char expected_args[] = "first\0second-argument";
+static const char expected_arg0[] = "first";
+static const char expected_arg1[] = "second-argument";
+
+int monitored_pid;
+int bprm_argc;
+int invalid_flags_ret;
+int copy_ret;
+int str_arg0_ret;
+int str_arg1_ret;
+int args_match;
+int str_args_match;
+
+extern int bpf_copy_from_user_bprm(void *dst, u32 dst__sz,
+				   const void *unsafe_ptr__ign,
+					   const struct linux_binprm *bprm,
+					   u64 flags) __ksym;
+
+extern int bpf_copy_from_user_bprm_str(void *dst, u32 dst__sz,
+				       const void *unsafe_ptr__ign,
+					       const struct linux_binprm *bprm,
+					       u64 flags) __ksym;
+
+SEC("lsm.s/bprm_check_security")
+int BPF_PROG(check_exec_args, struct linux_binprm *bprm, int ret)
+{
+	u32 pid = bpf_get_current_pid_tgid() >> 32;
+	char args[sizeof(expected_args)];
+	char arg0[32];
+	char arg1[32];
+
+	if (ret || pid != monitored_pid)
+		return ret;
+
+	bprm_argc = bprm->argc;
+
+	invalid_flags_ret = bpf_copy_from_user_bprm(args, sizeof(args),
+						    (void *)bprm->p, bprm, 1);
+
+	copy_ret = bpf_copy_from_user_bprm(args, sizeof(args),
+					   (void *)bprm->p, bprm, 0);
+	if (copy_ret)
+		return 0;
+
+	args_match = !__builtin_memcmp(args, expected_args, sizeof(expected_args));
+
+	str_arg0_ret = bpf_copy_from_user_bprm_str(arg0, sizeof(arg0),
+						   (void *)bprm->p, bprm,
+						BPF_F_PAD_ZEROS);
+	if (str_arg0_ret != sizeof(expected_arg0))
+		return 0;
+
+	str_arg1_ret = bpf_copy_from_user_bprm_str(arg1, sizeof(arg1),
+						   (void *)(bprm->p + str_arg0_ret),
+						bprm, BPF_F_PAD_ZEROS);
+	if (str_arg1_ret != sizeof(expected_arg1))
+		return 0;
+
+	str_args_match = !__builtin_memcmp(arg0, expected_arg0, sizeof(expected_arg0)) &&
+			!__builtin_memcmp(arg1, expected_arg1, sizeof(expected_arg1));
+
+	return args_match && str_args_match ? -EPERM : 0;
+}
-- 
2.55.0