selftests/bpf: Reject graph kptr use after RCU unlockgrafted

Add a sleepable verifier test that loads a graph-node local kptr in an
explicit RCU read-side critical section, then passes its node to
bpf_rbtree_remove() after the section ends.

Before the verifier fix, the stale NON_OWN_REF flag makes the node look like
a live borrowed reference and the program is accepted. After the fix, the
pointer is demoted without NON_OWN_REF and the graph kfunc argument is
rejected.

Also exercise a graph kptr loaded while a spin lock provides implicit RCU
protection. The pointer must be invalidated when the lock is released, which
guards the required ordering between non-owning-reference invalidation and
RCU demotion.

Update the existing fault-protected load test state description. The
post-unlock pointer no longer carries NON_OWN_REF, but remains readable
because the load is rewritten to use BPF_PROBE_MEM.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260904084325.52250-7-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 82 insertions, 0 deletions

diff --git a/samples/binderfs/binderfs_example.c b/samples/binderfs/binderfs_example.c
new file mode 100644
index 000000000..0fd92cdda
--- /dev/null
+++ b/samples/binderfs/binderfs_example.c
@@ -0,0 +1,82 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#define _GNU_SOURCE
+#include <errno.h>
+#include <fcntl.h>
+#include <sched.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <linux/android/binder.h>
+#include <linux/android/binderfs.h>
+
+int main(int argc, char *argv[])
+{
+	int fd, ret, saved_errno;
+	struct binderfs_device device = { 0 };
+
+	ret = unshare(CLONE_NEWNS);
+	if (ret < 0) {
+		fprintf(stderr, "%s - Failed to unshare mount namespace\n",
+			strerror(errno));
+		exit(EXIT_FAILURE);
+	}
+
+	ret = mount(NULL, "/", NULL, MS_REC | MS_PRIVATE, 0);
+	if (ret < 0) {
+		fprintf(stderr, "%s - Failed to mount / as private\n",
+			strerror(errno));
+		exit(EXIT_FAILURE);
+	}
+
+	ret = mkdir("/dev/binderfs", 0755);
+	if (ret < 0 && errno != EEXIST) {
+		fprintf(stderr, "%s - Failed to create binderfs mountpoint\n",
+			strerror(errno));
+		exit(EXIT_FAILURE);
+	}
+
+	ret = mount(NULL, "/dev/binderfs", "binder", 0, 0);
+	if (ret < 0) {
+		fprintf(stderr, "%s - Failed to mount binderfs\n",
+			strerror(errno));
+		exit(EXIT_FAILURE);
+	}
+
+	memcpy(device.name, "my-binder", strlen("my-binder"));
+
+	fd = open("/dev/binderfs/binder-control", O_RDONLY | O_CLOEXEC);
+	if (fd < 0) {
+		fprintf(stderr, "%s - Failed to open binder-control device\n",
+			strerror(errno));
+		exit(EXIT_FAILURE);
+	}
+
+	ret = ioctl(fd, BINDER_CTL_ADD, &device);
+	saved_errno = errno;
+	close(fd);
+	errno = saved_errno;
+	if (ret < 0) {
+		fprintf(stderr, "%s - Failed to allocate new binder device\n",
+			strerror(errno));
+		exit(EXIT_FAILURE);
+	}
+
+	printf("Allocated new binder device with major %d, minor %d, and name %s\n",
+	       device.major, device.minor, device.name);
+
+	ret = unlink("/dev/binderfs/my-binder");
+	if (ret < 0) {
+		fprintf(stderr, "%s - Failed to delete binder device\n",
+			strerror(errno));
+		exit(EXIT_FAILURE);
+	}
+
+	/* Cleanup happens when the mount namespace dies. */
+	exit(EXIT_SUCCESS);
+}