selftests/bpf: Extend test fs_kfuncs to cover security.bpf. xattr names

Extend test_progs fs_kfuncs to cover different xattr names. Specifically:
xattr name "user.kfuncs" and "security.bpf.xxx" can be read from BPF
program with kfuncs bpf_get_[file|dentry]_xattr(); while "security.bpf"
and "security.selinux" cannot be read.

Signed-off-by: Song Liu <song@kernel.org>

Author: liu-song-6

tools/testing/selftests/bpf/prog_tests/fs_kfuncs.c

@@ -12,7 +12,7 @@
 
 static const char testfile[] = "/tmp/test_progs_fs_kfuncs";
 
-static void test_xattr(void)
+static void test_get_xattr(const char *name, const char *value, bool allow_access)
 {
 	struct test_get_xattr *skel = NULL;
 	int fd = -1, err;
@@ -25,7 +25,7 @@ static void test_xattr(void)
 	close(fd);
 	fd = -1;
 
-	err = setxattr(testfile, "user.kfuncs", "hello", sizeof("hello"), 0);
+	err = setxattr(testfile, name, value, strlen(value) + 1, 0);
 	if (err && errno == EOPNOTSUPP) {
 		printf("%s:SKIP:local fs doesn't support xattr (%d)\n"
 		       "To run this test, make sure /tmp filesystem supports xattr.\n",
@@ -48,16 +48,23 @@ static void test_xattr(void)
 		goto out;
 
 	fd = open(testfile, O_RDONLY, 0644);
+
 	if (!ASSERT_GE(fd, 0, "open_file"))
 		goto out;
 
-	ASSERT_EQ(skel->bss->found_xattr_from_file, 1, "found_xattr_from_file");
-
 	/* Trigger security_inode_getxattr */
-	err = getxattr(testfile, "user.kfuncs", v, sizeof(v));
-	ASSERT_EQ(err, -1, "getxattr_return");
-	ASSERT_EQ(errno, EINVAL, "getxattr_errno");
-	ASSERT_EQ(skel->bss->found_xattr_from_dentry, 1, "found_xattr_from_dentry");
+	err = getxattr(testfile, name, v, sizeof(v));
+
+	if (allow_access) {
+		ASSERT_EQ(err, -1, "getxattr_return");
+		ASSERT_EQ(errno, EINVAL, "getxattr_errno");
+		ASSERT_EQ(skel->bss->found_xattr_from_file, 1, "found_xattr_from_file");
+		ASSERT_EQ(skel->bss->found_xattr_from_dentry, 1, "found_xattr_from_dentry");
+	} else {
+		ASSERT_EQ(err, strlen(value) + 1, "getxattr_return");
+		ASSERT_EQ(skel->bss->found_xattr_from_file, 0, "found_xattr_from_file");
+		ASSERT_EQ(skel->bss->found_xattr_from_dentry, 0, "found_xattr_from_dentry");
+	}
 
 out:
 	close(fd);
@@ -141,8 +148,18 @@ static void test_fsverity(void)
 
 void test_fs_kfuncs(void)
 {
-	if (test__start_subtest("xattr"))
-		test_xattr();
+	/* Matches xattr_names in progs/test_get_xattr.c */
+	if (test__start_subtest("user_xattr"))
+		test_get_xattr("user.kfuncs", "hello", true);
+
+	if (test__start_subtest("security_bpf_xattr"))
+		test_get_xattr("security.bpf.xxx", "hello", true);
+
+	if (test__start_subtest("security_bpf_xattr_error"))
+		test_get_xattr("security.bpf", "hello", false);
+
+	if (test__start_subtest("security_selinux_xattr_error"))
+		test_get_xattr("security.selinux", "hello", false);
 
 	if (test__start_subtest("fsverity"))
 		test_fsverity();

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

@@ -6,6 +6,7 @@
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_tracing.h>
 #include "bpf_kfuncs.h"
+#include "bpf_misc.h"
 
 char _license[] SEC("license") = "GPL";
 
@@ -17,20 +18,35 @@ static const char expected_value[] = "hello";
 char value1[32];
 char value2[32];
 
+/* Matches caller of test_get_xattr() in prog_tests/fs_kfuncs.c */
+static const char * const xattr_names[] = {
+	/* The following work. */
+	"user.kfuncs",
+	"security.bpf.xxx",
+
+	/* The following do not work. */
+	"security.bpf",
+	"security.selinux"
+};
+
 SEC("lsm.s/file_open")
 int BPF_PROG(test_file_open, struct file *f)
 {
 	struct bpf_dynptr value_ptr;
 	__u32 pid;
-	int ret;
+	int ret, i;
 
 	pid = bpf_get_current_pid_tgid() >> 32;
 	if (pid != monitored_pid)
 		return 0;
 
 	bpf_dynptr_from_mem(value1, sizeof(value1), 0, &value_ptr);
 
-	ret = bpf_get_file_xattr(f, "user.kfuncs", &value_ptr);
+	for (i = 0; i < ARRAY_SIZE(xattr_names); i++) {
+		ret = bpf_get_file_xattr(f, xattr_names[i], &value_ptr);
+		if (ret == sizeof(expected_value))
+			break;
+	}
 	if (ret != sizeof(expected_value))
 		return 0;
 	if (bpf_strncmp(value1, ret, expected_value))
@@ -44,15 +60,19 @@ int BPF_PROG(test_inode_getxattr, struct dentry *dentry, char *name)
 {
 	struct bpf_dynptr value_ptr;
 	__u32 pid;
-	int ret;
+	int ret, i;
 
 	pid = bpf_get_current_pid_tgid() >> 32;
 	if (pid != monitored_pid)
 		return 0;
 
 	bpf_dynptr_from_mem(value2, sizeof(value2), 0, &value_ptr);
 
-	ret = bpf_get_dentry_xattr(dentry, "user.kfuncs", &value_ptr);
+	for (i = 0; i < ARRAY_SIZE(xattr_names); i++) {
+		ret = bpf_get_dentry_xattr(dentry, xattr_names[i], &value_ptr);
+		if (ret == sizeof(expected_value))
+			break;
+	}
 	if (ret != sizeof(expected_value))
 		return 0;
 	if (bpf_strncmp(value2, ret, expected_value))