selftests/bpf: Test kfuncs that set and remove xattr from BPF programs

Two sets of tests are added to exercise the not _locked and _locked
version of the kfuncs. For both tests, user space accesses xattr
security.bpf.foo on a testfile. The BPF program is triggered by user
space access (on LSM hook inode_[set|get]_xattr) and sets or removes
xattr security.bpf.bar. Then user space then validates that xattr
security.bpf.bar is set or removed as expected.

Note that, in both tests, the BPF programs use the not _locked kfuncs.
The verifier picks the proper kfuncs based on the calling context.

Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20250130213549.3353349-6-song@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 125 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/prog_tests/fs_kfuncs.c b/tools/testing/selftests/bpf/prog_tests/fs_kfuncs.c
index 419f45b56472..43a26ec69a8e 100644
--- a/tools/testing/selftests/bpf/prog_tests/fs_kfuncs.c
+++ b/tools/testing/selftests/bpf/prog_tests/fs_kfuncs.c
@@ -8,6 +8,7 @@
 #include <unistd.h>
 #include <test_progs.h>
 #include "test_get_xattr.skel.h"
+#include "test_set_remove_xattr.skel.h"
 #include "test_fsverity.skel.h"
 
 static const char testfile[] = "/tmp/test_progs_fs_kfuncs";
@@ -72,6 +73,127 @@ out:
 	remove(testfile);
 }
 
+/* xattr value we will set to security.bpf.foo */
+static const char value_foo[] = "hello";
+
+static void read_and_validate_foo(struct test_set_remove_xattr *skel)
+{
+	char value_out[32];
+	int err;
+
+	err = getxattr(testfile, skel->rodata->xattr_foo, value_out, sizeof(value_out));
+	ASSERT_EQ(err, sizeof(value_foo), "getxattr size foo");
+	ASSERT_EQ(strncmp(value_out, value_foo, sizeof(value_foo)), 0, "strncmp value_foo");
+}
+
+static void set_foo(struct test_set_remove_xattr *skel)
+{
+	ASSERT_OK(setxattr(testfile, skel->rodata->xattr_foo, value_foo, strlen(value_foo) + 1, 0),
+		  "setxattr foo");
+}
+
+static void validate_bar_match(struct test_set_remove_xattr *skel)
+{
+	char value_out[32];
+	int err;
+
+	err = getxattr(testfile, skel->rodata->xattr_bar, value_out, sizeof(value_out));
+	ASSERT_EQ(err, sizeof(skel->data->value_bar), "getxattr size bar");
+	ASSERT_EQ(strncmp(value_out, skel->data->value_bar, sizeof(skel->data->value_bar)), 0,
+		  "strncmp value_bar");
+}
+
+static void validate_bar_removed(struct test_set_remove_xattr *skel)
+{
+	char value_out[32];
+	int err;
+
+	err = getxattr(testfile, skel->rodata->xattr_bar, value_out, sizeof(value_out));
+	ASSERT_LT(err, 0, "getxattr size bar should fail");
+}
+
+static void test_set_remove_xattr(void)
+{
+	struct test_set_remove_xattr *skel = NULL;
+	int fd = -1, err;
+
+	fd = open(testfile, O_CREAT | O_RDONLY, 0644);
+	if (!ASSERT_GE(fd, 0, "create_file"))
+		return;
+
+	close(fd);
+	fd = -1;
+
+	skel = test_set_remove_xattr__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "test_set_remove_xattr__open_and_load"))
+		return;
+
+	/* Set security.bpf.foo to "hello" */
+	err = setxattr(testfile, skel->rodata->xattr_foo, value_foo, strlen(value_foo) + 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",
+		       __func__, errno);
+		test__skip();
+		goto out;
+	}
+
+	if (!ASSERT_OK(err, "setxattr"))
+		goto out;
+
+	skel->bss->monitored_pid = getpid();
+	err = test_set_remove_xattr__attach(skel);
+	if (!ASSERT_OK(err, "test_set_remove_xattr__attach"))
+		goto out;
+
+	/* First, test not _locked version of the kfuncs with getxattr. */
+
+	/* Read security.bpf.foo and trigger test_inode_getxattr. This
+	 * bpf program will set security.bpf.bar to "world".
+	 */
+	read_and_validate_foo(skel);
+	validate_bar_match(skel);
+
+	/* Read security.bpf.foo and trigger test_inode_getxattr again.
+	 * This will remove xattr security.bpf.bar.
+	 */
+	read_and_validate_foo(skel);
+	validate_bar_removed(skel);
+
+	ASSERT_TRUE(skel->bss->set_security_bpf_bar_success, "set_security_bpf_bar_success");
+	ASSERT_TRUE(skel->bss->remove_security_bpf_bar_success, "remove_security_bpf_bar_success");
+	ASSERT_TRUE(skel->bss->set_security_selinux_fail, "set_security_selinux_fail");
+	ASSERT_TRUE(skel->bss->remove_security_selinux_fail, "remove_security_selinux_fail");
+
+	/* Second, test _locked version of the kfuncs, with setxattr */
+
+	/* Set security.bpf.foo and trigger test_inode_setxattr. This
+	 * bpf program will set security.bpf.bar to "world".
+	 */
+	set_foo(skel);
+	validate_bar_match(skel);
+
+	/* Set security.bpf.foo and trigger test_inode_setxattr again.
+	 * This will remove xattr security.bpf.bar.
+	 */
+	set_foo(skel);
+	validate_bar_removed(skel);
+
+	ASSERT_TRUE(skel->bss->locked_set_security_bpf_bar_success,
+		    "locked_set_security_bpf_bar_success");
+	ASSERT_TRUE(skel->bss->locked_remove_security_bpf_bar_success,
+		    "locked_remove_security_bpf_bar_success");
+	ASSERT_TRUE(skel->bss->locked_set_security_selinux_fail,
+		    "locked_set_security_selinux_fail");
+	ASSERT_TRUE(skel->bss->locked_remove_security_selinux_fail,
+		    "locked_remove_security_selinux_fail");
+
+out:
+	close(fd);
+	test_set_remove_xattr__destroy(skel);
+	remove(testfile);
+}
+
 #ifndef SHA256_DIGEST_SIZE
 #define SHA256_DIGEST_SIZE      32
 #endif
@@ -161,6 +283,9 @@ void test_fs_kfuncs(void)
 	if (test__start_subtest("security_selinux_xattr_error"))
 		test_get_xattr("security.selinux", "hello", false);
 
+	if (test__start_subtest("set_remove_xattr"))
+		test_set_remove_xattr();
+
 	if (test__start_subtest("fsverity"))
 		test_fsverity();
 }