bpf: mark a NULL kfunc argument precisegrafted

check_kfunc_arg() allows bpf_register_is_null() for nullable arguments
w/o marking the underlying scalar register precise. Hence a checkpoint
created on such a path would prune against arbitrary scalar value.

Fixes: 3bda08b63670 ("bpf: Allow NULL buffers in bpf_dynptr_slice(_rw)")
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20260904-register-is-null-precise-fixes-v1-5-0f5a360ff15d@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 31 insertions, 0 deletions

diff --git a/security/lsm_notifier.c b/security/lsm_notifier.c
new file mode 100644
index 000000000..c92fad5d5
--- /dev/null
+++ b/security/lsm_notifier.c
@@ -0,0 +1,31 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * LSM notifier functions
+ *
+ */
+
+#include <linux/notifier.h>
+#include <linux/security.h>
+
+static BLOCKING_NOTIFIER_HEAD(blocking_lsm_notifier_chain);
+
+int call_blocking_lsm_notifier(enum lsm_event event, void *data)
+{
+	return blocking_notifier_call_chain(&blocking_lsm_notifier_chain,
+					    event, data);
+}
+EXPORT_SYMBOL(call_blocking_lsm_notifier);
+
+int register_blocking_lsm_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_register(&blocking_lsm_notifier_chain,
+						nb);
+}
+EXPORT_SYMBOL(register_blocking_lsm_notifier);
+
+int unregister_blocking_lsm_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_unregister(&blocking_lsm_notifier_chain,
+						  nb);
+}
+EXPORT_SYMBOL(unregister_blocking_lsm_notifier);