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, 24 insertions, 0 deletions

diff --git a/fs/proc/cmdline.c b/fs/proc/cmdline.c
new file mode 100644
index 000000000..a6f761219
--- /dev/null
+++ b/fs/proc/cmdline.c
@@ -0,0 +1,24 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/fs.h>
+#include <linux/init.h>
+#include <linux/proc_fs.h>
+#include <linux/seq_file.h>
+#include "internal.h"
+
+static int cmdline_proc_show(struct seq_file *m, void *v)
+{
+	seq_puts(m, saved_command_line);
+	seq_putc(m, '\n');
+	return 0;
+}
+
+static int __init proc_cmdline_init(void)
+{
+	struct proc_dir_entry *pde;
+
+	pde = proc_create_single("cmdline", 0, NULL, cmdline_proc_show);
+	pde_make_permanent(pde);
+	pde->size = saved_command_line_len + 1;
+	return 0;
+}
+fs_initcall(proc_cmdline_init);