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, 80 insertions, 0 deletions

diff --git a/fs/cramfs/uncompress.c b/fs/cramfs/uncompress.c
new file mode 100644
index 000000000..975d98fc2
--- /dev/null
+++ b/fs/cramfs/uncompress.c
@@ -0,0 +1,80 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * uncompress.c
+ *
+ * (C) Copyright 1999 Linus Torvalds
+ *
+ * cramfs interfaces to the uncompression library. There's really just
+ * three entrypoints:
+ *
+ *  - cramfs_uncompress_init() - called to initialize the thing.
+ *  - cramfs_uncompress_exit() - tell me when you're done
+ *  - cramfs_uncompress_block() - uncompress a block.
+ *
+ * NOTE NOTE NOTE! The uncompression is entirely single-threaded. We
+ * only have one stream, and we'll initialize it only once even if it
+ * then is used by multiple filesystems.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/vmalloc.h>
+#include <linux/zlib.h>
+#include "internal.h"
+
+static z_stream stream;
+static int initialized;
+
+/* Returns length of decompressed data. */
+int cramfs_uncompress_block(void *dst, int dstlen, void *src, int srclen)
+{
+	int err;
+
+	stream.next_in = src;
+	stream.avail_in = srclen;
+
+	stream.next_out = dst;
+	stream.avail_out = dstlen;
+
+	err = zlib_inflateReset(&stream);
+	if (err != Z_OK) {
+		pr_err("zlib_inflateReset error %d\n", err);
+		zlib_inflateEnd(&stream);
+		zlib_inflateInit(&stream);
+	}
+
+	err = zlib_inflate(&stream, Z_FINISH);
+	if (err != Z_STREAM_END)
+		goto err;
+	return stream.total_out;
+
+err:
+	pr_err("Error %d while decompressing!\n", err);
+	pr_err("%p(%d)->%p(%d)\n", src, srclen, dst, dstlen);
+	return -EIO;
+}
+
+int cramfs_uncompress_init(void)
+{
+	if (!initialized++) {
+		stream.workspace = vmalloc(zlib_inflate_workspacesize());
+		if (!stream.workspace) {
+			initialized = 0;
+			return -ENOMEM;
+		}
+		stream.next_in = NULL;
+		stream.avail_in = 0;
+		zlib_inflateInit(&stream);
+	}
+	return 0;
+}
+
+void cramfs_uncompress_exit(void)
+{
+	if (!--initialized) {
+		zlib_inflateEnd(&stream);
+		vfree(stream.workspace);
+	}
+}