selftests/bpf: Test rhtab kptr cancellation semanticsgrafted

Resizable hash-map updates and deletions must not perform full special-field
destruction in their caller context. In particular, a referenced kptr must
remain attached to the allocation until the memory allocator destructor can
release it safely.

Add separate coverage for both affected paths. The update test stores a task
kptr, replaces the ordinary value bytes with BPF_EXIST, and verifies that the
kptr survived. The delete test removes an element and exchanges its kptr
through the still-valid map-value pointer before the allocation is reclaimed.

Both cases observe a NULL kptr when rhtab uses bpf_obj_free_fields(). They
recover and release the reference after rhtab switches to cancellation
semantics.

Signed-off-by: Nuoqi Gui <gnq25@mails.tsinghua.edu.cn>
[ kkd: Split update and delete coverage and rewrote the commit log ]
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260904104203.345917-5-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

2 files changed, 47 insertions, 0 deletions

diff --git a/security/bpf/Makefile b/security/bpf/Makefile
new file mode 100644
index 000000000..c7a89a962
--- /dev/null
+++ b/security/bpf/Makefile
@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Copyright (C) 2020 Google LLC.
+
+obj-$(CONFIG_BPF_LSM) := hooks.o
diff --git a/security/bpf/hooks.c b/security/bpf/hooks.c
new file mode 100644
index 000000000..7b98f5d1e
--- /dev/null
+++ b/security/bpf/hooks.c
@@ -0,0 +1,42 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Copyright (C) 2020 Google LLC.
+ */
+#include <linux/lsm_hooks.h>
+#include <linux/bpf_lsm.h>
+#include <uapi/linux/lsm.h>
+
+bool bpf_lsm_initialized __ro_after_init;
+
+static struct security_hook_list bpf_lsm_hooks[] __ro_after_init = {
+	#define LSM_HOOK(RET, DEFAULT, NAME, ...) \
+	LSM_HOOK_INIT(NAME, bpf_lsm_##NAME),
+	#include <linux/lsm_hook_defs.h>
+	#undef LSM_HOOK
+	LSM_HOOK_INIT(inode_free_security, bpf_inode_storage_free),
+};
+
+static const struct lsm_id bpf_lsmid = {
+	.name = "bpf",
+	.id = LSM_ID_BPF,
+};
+
+static int __init bpf_lsm_init(void)
+{
+	security_add_hooks(bpf_lsm_hooks, ARRAY_SIZE(bpf_lsm_hooks),
+			   &bpf_lsmid);
+	bpf_lsm_initialized = true;
+	pr_info("LSM support for eBPF active\n");
+	return 0;
+}
+
+struct lsm_blob_sizes bpf_lsm_blob_sizes __ro_after_init = {
+	.lbs_inode = sizeof(struct bpf_storage_blob),
+};
+
+DEFINE_LSM(bpf) = {
+	.id = &bpf_lsmid,
+	.init = bpf_lsm_init,
+	.blobs = &bpf_lsm_blob_sizes
+};