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>

1 files changed, 56 insertions, 0 deletions

diff --git a/lib/netdev-notifier-error-inject.c b/lib/netdev-notifier-error-inject.c
new file mode 100644
index 000000000..bb930f279
--- /dev/null
+++ b/lib/netdev-notifier-error-inject.c
@@ -0,0 +1,56 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/netdevice.h>
+
+#include "notifier-error-inject.h"
+
+static int priority;
+module_param(priority, int, 0);
+MODULE_PARM_DESC(priority, "specify netdevice notifier priority");
+
+static struct notifier_err_inject netdev_notifier_err_inject = {
+	.actions = {
+		{ NOTIFIER_ERR_INJECT_ACTION(NETDEV_REGISTER) },
+		{ NOTIFIER_ERR_INJECT_ACTION(NETDEV_CHANGEMTU) },
+		{ NOTIFIER_ERR_INJECT_ACTION(NETDEV_CHANGENAME) },
+		{ NOTIFIER_ERR_INJECT_ACTION(NETDEV_PRE_UP) },
+		{ NOTIFIER_ERR_INJECT_ACTION(NETDEV_PRE_TYPE_CHANGE) },
+		{ NOTIFIER_ERR_INJECT_ACTION(NETDEV_POST_INIT) },
+		{ NOTIFIER_ERR_INJECT_ACTION(NETDEV_PRECHANGEMTU) },
+		{ NOTIFIER_ERR_INJECT_ACTION(NETDEV_PRECHANGEUPPER) },
+		{ NOTIFIER_ERR_INJECT_ACTION(NETDEV_CHANGEUPPER) },
+		{}
+	}
+};
+
+static struct dentry *dir;
+
+static int netdev_err_inject_init(void)
+{
+	int err;
+
+	dir = notifier_err_inject_init("netdev", notifier_err_inject_dir,
+				       &netdev_notifier_err_inject, priority);
+	if (IS_ERR(dir))
+		return PTR_ERR(dir);
+
+	err = register_netdevice_notifier(&netdev_notifier_err_inject.nb);
+	if (err)
+		debugfs_remove_recursive(dir);
+
+	return err;
+}
+
+static void netdev_err_inject_exit(void)
+{
+	unregister_netdevice_notifier(&netdev_notifier_err_inject.nb);
+	debugfs_remove_recursive(dir);
+}
+
+module_init(netdev_err_inject_init);
+module_exit(netdev_err_inject_exit);
+
+MODULE_DESCRIPTION("Netdevice notifier error injection module");
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Nikolay Aleksandrov <razor@blackwall.org>");