[patch net-next v4 5/9] genetlink: introduce per-sock family private pointer storage

Jiri Pirko
2023-11-23T18:15:57Z

From: Jiri Pirko <jiri@nvidia.com>

Introduce a priv pointer into struct netlink_sock. Use it to store a per
socket xarray that contains family->id indexed priv pointer storage.
Note I used xarray instead of suggested linked list as it is more
convenient, without need to have a container struct that would
contain struct list_head item.

Introduce genl_sk_priv_store() to store the priv pointer.
Introduce genl_sk_priv_get() to obtain the priv pointer under RCU
read lock.

Assume that kfree() is good for free of privs for now, as the only user
introduced by the follow-up patch (devlink) will use kzalloc() for the
allocation of the memory of the stored pointer. If later on
this needs to be made custom, a callback is going to be needed.
Until then (if ever), do this in a simple way.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
---
v3->v4:
- new patch
---
include/net/genetlink.h | 3 ++
net/netlink/af_netlink.h | 1 +
net/netlink/genetlink.c | 98 ++++++++++++++++++++++++++++++++++++++++
3 files changed, 102 insertions(+)

diff --git a/include/net/genetlink.h b/include/net/genetlink.h
index e18a4c0d69ee..66c1e50415e0 100644
--- a/include/net/genetlink.h
+++ b/include/net/genetlink.h
@@ -300,6 +300,9 @@ int genl_register_family(struct genl_family *family);
int genl_unregister_family(const struct genl_family *family);
void genl_notify(const struct genl_family *family, struct sk_buff *skb,
struct genl_info *info, u32 group, gfp_t flags);
+void *genl_sk_priv_get(struct sock *sk, struct genl_family *family);
+void *genl_sk_priv_store(struct sock *sk, struct genl_family *family,
+ void *priv);

void *genlmsg_put(struct sk_buff *skb, u32 portid, u32 seq,
const struct genl_family *family, int flags, u8 cmd);
diff --git a/net/netlink/af_netlink.h b/net/netlink/af_netlink.h
index 2145979b9986..5d96135a4cf3 100644
--- a/net/netlink/af_netlink.h
+++ b/net/netlink/af_netlink.h
@@ -51,6 +51,7 @@ struct netlink_sock {
struct rhash_head node;
struct rcu_head rcu;
struct work_struct work;
+ void __rcu *priv;
};

static inline struct netlink_sock *nlk_sk(struct sock *sk)
diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c
index 92ef5ed2e7b0..aae5e63fa50b 100644
--- a/net/netlink/genetlink.c
+++ b/net/netlink/genetlink.c
@@ -21,6 +21,7 @@
#include <linux/idr.h>
#include <net/sock.h>
#include <net/genetlink.h>
+#include "af_netlink.h"

static DEFINE_MUTEX(genl_mutex); /* serialization of message processing */
static DECLARE_RWSEM(cb_lock);
@@ -1699,12 +1700,109 @@ static int genl_bind(struct net *net, int group)
return ret;
}

+struct genl_sk_ctx {
+ struct xarray family_privs;
+};
+
+static struct genl_sk_ctx *genl_sk_ctx_alloc(void)
+{
+ struct genl_sk_ctx *ctx;
+
+ ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
+ if (!ctx)
+ return NULL;
+ xa_init_flags(&ctx->family_privs, XA_FLAGS_ALLOC);
+ return ctx;
+}
+
+static void genl_sk_ctx_free(struct genl_sk_ctx *ctx)
+{
+ unsigned long family_id;
+ void *priv;
+
+ xa_for_each(&ctx->family_privs, family_id, priv) {
+ xa_erase(&ctx->family_privs, family_id);
+ kfree(priv);
+ }
+ xa_destroy(&ctx->family_privs);
+ kfree(ctx);
+}
+
+/**
+ * genl_sk_priv_get - Get per-socket private pointer for family
+ *
+ * @sk: socket
+ * @family: family
+ *
+ * Lookup a private pointer stored per-socket by a specified
+ * Generic netlink family.
+ *
+ * Caller should make sure this is called in RCU read locked section.
+ *
+ * Returns: valid pointer on success, otherwise NULL.
+ */
+void *genl_sk_priv_get(struct sock *sk, struct genl_family *family)
+{
+ struct genl_sk_ctx *ctx;
+
+ ctx = rcu_dereference(nlk_sk(sk)->priv);
+ if (!ctx)
+ return NULL;
+ return xa_load(&ctx->family_privs, family->id);
+}
+
+/**
+ * genl_sk_priv_store - Store per-socket private pointer for family
+ *
+ * @sk: socket
+ * @family: family
+ * @priv: private pointer
+ *
+ * Store a private pointer per-socket for a specified
+ * Generic netlink family.
+ *
+ * Caller has to make sure this is not called in parallel multiple times
+ * for the same sock and also in parallel to genl_release() for the same sock.
+ *
+ * Returns: previously stored private pointer for the family (could be NULL)
+ * on success, otherwise negative error value encoded by ERR_PTR().
+ */
+void *genl_sk_priv_store(struct sock *sk, struct genl_family *family,
+ void *priv)
+{
+ struct genl_sk_ctx *ctx;
+ void *old_priv;
+
+ ctx = rcu_dereference_raw(nlk_sk(sk)->priv);
+ if (!ctx) {
+ ctx = genl_sk_ctx_alloc();
+ if (!ctx)
+ return ERR_PTR(-ENOMEM);
+ rcu_assign_pointer(nlk_sk(sk)->priv, ctx);
+ }
+
+ old_priv = xa_store(&ctx->family_privs, family->id, priv, GFP_KERNEL);
+ if (xa_is_err(old_priv))
+ return ERR_PTR(xa_err(old_priv));
+ return old_priv;
+}
+
+static void genl_release(struct sock *sk, unsigned long *groups)
+{
+ struct genl_sk_ctx *ctx;
+
+ ctx = rcu_dereference_raw(nlk_sk(sk)->priv);
+ if (ctx)
+ genl_sk_ctx_free(ctx);
+}
+
static int __net_init genl_pernet_init(struct net *net)
{
struct netlink_kernel_cfg cfg = {
.input = genl_rcv,
.flags = NL_CFG_F_NONROOT_RECV,
.bind = genl_bind,
+ .release = genl_release,
};

/* we'll bump the group number right afterwards */
--
2.41.0