In Xtables1/iptables, atomic table replace was easy, since userspace
practically only had to do a single kernel call (SO_SET_REPLACE) and
the kernel got the entire ruleset at once.
With Netlink (and its limitations), the kernel module instead will
have to collect chain/rule modification messages first. This requires
a temporary scratch area preserved across Netlink message calls,
implemented herein in struct xtnetlink_transact, which is logically
attached to the invoking Netlink socket.
This commit adds the commit side, which does not do anything by
itself, but needs an operation that starts a transaction, like the
following NFXTM_REPLACE. (The commit split is for supposedly easier
review.)
Signed-off-by: Jan Engelhardt <jengelh@xxxxxxx>
---
include/net/netfilter/xt_core.h | 3 +
include/uapi/linux/netfilter/nfnetlink_xtables.h | 9 ++
net/netfilter/xt_core.c | 6 +-
net/netfilter/xt_nfnetlink.c | 166 ++++++++++++++++++++++
4 files changed, 182 insertions(+), 2 deletions(-)
diff --git a/include/net/netfilter/xt_core.h b/include/net/netfilter/xt_core.h
index cfd09fa..b0b496f 100644
--- a/include/net/netfilter/xt_core.h
+++ b/include/net/netfilter/xt_core.h
@@ -44,4 +44,7 @@ extern void xt2_chain_free(struct xt2_chain *);
extern struct xt2_chain *xt2_chain_move(struct xt2_table *, const char *,
const char *);
+extern struct xt2_table *xt2_table_new(void);
+extern void xt2_table_free(struct xt2_table *);
+
#endif /* _NETFILTER_XTCORE_H */
diff --git a/include/uapi/linux/netfilter/nfnetlink_xtables.h b/include/uapi/linux/netfilter/nfnetlink_xtables.h
index 1f66720..bec4d054 100644
--- a/include/uapi/linux/netfilter/nfnetlink_xtables.h
+++ b/include/uapi/linux/netfilter/nfnetlink_xtables.h
@@ -9,6 +9,8 @@
* %NFXTM_CHAIN_NEW: request creation of a chain by name
* %NFXTM_CHAIN_DEL: request deletion of a chain by name
* %NFXTM_CHAIN_MOVE: rename a chain
+ * %NFXTM_COMMIT: finalize and commit a transaction
+ * %NFXTM_TABLE_REPLACE:start a table replace transaction
*/
enum nfxt_msg_type {
NFXTM_IDENTIFY = 1,
@@ -16,6 +18,8 @@ enum nfxt_msg_type {
NFXTM_CHAIN_NEW,
NFXTM_CHAIN_DEL,
NFXTM_CHAIN_MOVE,
+ NFXTM_COMMIT,
+ NFXTM_TABLE_REPLACE,
};
/**
@@ -40,6 +44,9 @@ enum nfxt_attr_type {
* %NFXTE_CHAIN_EXIST: Chain already exists
* %NFXTE_CHAIN_NOENT: Chain does not exist
* %NFXTE_CHAIN_NAMETOOLONG: New chain name is too long
+ * %NFXTE_TRANSACT_ACTIVE: Attempted to start transaction while one was
+ * already active
+ * %NFXTE_TRANSACT_INACTIVE: Commit issued when no transaction active
*/
enum nfxt_errno {
NFXTE_SUCCESS = 0,
@@ -48,6 +55,8 @@ enum nfxt_errno {
NFXTE_CHAIN_EXISTS,
NFXTE_CHAIN_NOENT,
NFXTE_CHAIN_NAMETOOLONG,
+ NFXTE_TRANSACT_ACTIVE,
+ NFXTE_TRANSACT_INACTIVE,
};
#endif /* _LINUX_NFNETLINK_XTABLES_H */
diff --git a/net/netfilter/xt_core.c b/net/netfilter/xt_core.c
index 289ab5063..7c00e2d 100644
--- a/net/netfilter/xt_core.c
+++ b/net/netfilter/xt_core.c
@@ -132,7 +132,7 @@ struct xt2_chain *xt2_chain_move(struct xt2_table *table, const char *old_name,
/**
* Create a new table with no chains and no rules.
*/
-static struct xt2_table *xt2_table_new(void)
+struct xt2_table *xt2_table_new(void)
{
struct xt2_table *table;
@@ -145,10 +145,12 @@ static struct xt2_table *xt2_table_new(void)
return table;
}
-static void xt2_table_free(struct xt2_table *table)
+void xt2_table_free(struct xt2_table *table)
{
struct xt2_chain *chain, *next;
+ if (table == NULL)
+ return;
list_for_each_entry_safe(chain, next, &table->chain_list, anchor)
xt2_chain_free(chain);
kfree(table);
diff --git a/net/netfilter/xt_nfnetlink.c b/net/netfilter/xt_nfnetlink.c
index 9fc18c4..02f19fa 100644
--- a/net/netfilter/xt_nfnetlink.c
+++ b/net/netfilter/xt_nfnetlink.c
@@ -7,18 +7,25 @@
* the Free Software Foundation, either version 2 of the License, or
* (at your option) any later version.
*/
+#include <linux/atomic.h>
#include <linux/err.h>
#include <linux/errno.h>
#include <linux/kernel.h>
+#include <linux/list.h>
#include <linux/module.h>
#include <linux/netlink.h>
+#include <linux/notifier.h>
+#include <linux/rwlock.h>
#include <linux/skbuff.h>
+#include <linux/wait.h>
#include <linux/netfilter.h>
#include <linux/netfilter/nfnetlink.h>
#include <linux/netfilter/nfnetlink_xtables.h>
#include <net/netlink.h>
+#include <net/net_namespace.h>
#include <net/sock.h>
#include <net/netfilter/xt_core.h>
+#include <asm-generic/bug.h>
#include "xt_nfnetlink.h"
#define MAKE_TAGGED_TYPE(x) ((x) | (NFNL_SUBSYS_XTABLES << 8))
@@ -40,6 +47,100 @@ struct xtnetlink_pktref {
};
/**
+ * Per-client transaction state
+ * @netns: part of the tuple to uniquely identify client
+ * @use_count: tracking active operations on the TA's table
+ * @nladdr: client address
+ * @table: temporary new table
+ *
+ * Because Netlink attrs can only be so big, the kernel won't be seeing the
+ * entire ruleset at once from userspace, but has to collect it piecewise.
+ *
+ * @use_count is necessarily zero if no xtnl kernel code currently executes.
+ */
+struct xtnetlink_transact {
+ struct list_head anchor;
+ const struct net *netns;
+ uint32_t nladdr;
+ atomic_t use_count;
+ wait_queue_head_t waitq;
+ struct xt2_table *table;
+};
+
+/**
+ * Write-locked: the one user may add/delete entries to/from transact_list
+ * Read-locked: users only touch transaction entries' content
+ */
+static rwlock_t xtnetlink_transact_lock;
+static LIST_HEAD(xtnetlink_transact_list);
+
+/**
+ * Find and return the transaction state.
+ * @net: network namespace of socket
+ * @nladdr: client address (NETLINK_CB(skb).portid)
+ *
+ * The caller should hold appropriate locks.
+ */
+static struct xtnetlink_transact *
+xtnetlink_transact_lookup(const struct net *netns, uint32_t nladdr)
+{
+ struct xtnetlink_transact *e;
+
+ list_for_each_entry(e, &xtnetlink_transact_list, anchor)
+ if (net_eq(e->netns, netns) && e->nladdr == nladdr)
+ return e;
+ return NULL;
+}
+
+/**
+ * Lookup and pin the transaction state for a given client.
+ * @net: network namespace of socket
+ * @nladdr: client address (NETLINK_CB(skb).portid)
+ *
+ * Retrieves the current TA for the client.
+ * The read lock ensures that no entry is going to disappear during the search.
+ */
+static struct xtnetlink_transact *
+xtnetlink_transact_get(struct net *netns, uint32_t nladdr)
+{
+ struct xtnetlink_transact *xa;
+
+ read_lock(&xtnetlink_transact_lock);
+ xa = xtnetlink_transact_lookup(netns, nladdr);
+ if (xa != NULL)
+ atomic_inc(&xa->use_count);
+ read_unlock(&xtnetlink_transact_lock);
+ return xa;
+}
+
+/**
+ * Drain all modifications to the transaction.
+ *
+ * Removes the transaction from the list and wait for all outstanding
+ * operations on it to finish, so that the caller becomes the exclusive holder
+ * of the structure.
+ */
+static void xtnetlink_transact_pop(struct xtnetlink_transact *xa)
+{
+ WARN_ON(atomic_read(&xa->use_count) == 0);
+ atomic_dec(&xa->use_count);
+
+ /* Guarantee that no new modifications will come in to this TA. */
+ write_lock(&xtnetlink_transact_lock);
+ list_del(&xa->anchor);
+ write_unlock(&xtnetlink_transact_lock);
+
+ while (atomic_read(&xa->use_count) > 0)
+ wait_event(xa->waitq, atomic_read(&xa->use_count) == 0);
+}
+
+static void xtnetlink_transact_free(struct xtnetlink_transact *xa)
+{
+ xt2_table_free(xa->table);
+ kfree(xa);
+}
+
+/**
* @skb: outgoing skb
* @old: pointers to the original incoming skb/nl headers
* @flags: extra flags to set in nlmsg
@@ -300,6 +401,33 @@ xtnetlink_chain_move(struct sock *xtnl, struct sk_buff *iskb,
}
}
+static int
+xtnetlink_commit(struct sock *xtnl, struct sk_buff *iskb,
+ const struct nlmsghdr *imsg, const struct nlattr *const *ad)
+{
+ struct xt2_pernet_data *pnet = xtables2_pernet(sock_net(xtnl));
+ struct xtnetlink_pktref ref =
+ {.c_skb = iskb, .c_msg = imsg, .sock = xtnl};
+ struct xtnetlink_transact *xa;
+ struct xt2_table *old_table;
+
+ xa = xtnetlink_transact_get(sock_net(xtnl), NETLINK_CB(iskb).portid);
+ if (xa == NULL)
+ return xtnetlink_error(&ref, NFXTE_TRANSACT_INACTIVE);
+
+ xtnetlink_transact_pop(xa);
+
+ /* <- ruleset verification/packing here */
+ mutex_lock(&pnet->master_lock);
+ old_table = pnet->master;
+ rcu_assign_pointer(pnet->master, xa->table);
+ mutex_unlock(&pnet->master_lock);
+ /* Just (re)use transact_free to kill the old table off. */
+ xa->table = old_table;
+ xtnetlink_transact_free(xa);
+ return xtnetlink_error(&ref, NFXTE_SUCCESS);
+}
+
static const struct nla_policy xtnetlink_policy[] = {
[NFXTA_NAME] = {.type = NLA_NUL_STRING},
[NFXTA_ERRNO] = {.type = NLA_U32},
@@ -321,6 +449,7 @@ static const struct nfnl_callback xtnetlink_callback[] = {
[NFXTM_CHAIN_NEW] = {.call = xtnetlink_chain_new, pol},
[NFXTM_CHAIN_DEL] = {.call = xtnetlink_chain_del, pol},
[NFXTM_CHAIN_MOVE] = {.call = xtnetlink_chain_move, pol},
+ [NFXTM_COMMIT] = {.call = xtnetlink_commit, pol},
};
#undef pol
@@ -331,14 +460,51 @@ static const struct nfnetlink_subsystem xtnetlink_subsys = {
.cb_count = ARRAY_SIZE(xtnetlink_callback),
};
+static int
+xtnetlink_nlevent(struct notifier_block *blk, unsigned long event, void *ptr)
+{
+ const struct netlink_notify *note = ptr;
+ struct xtnetlink_transact *xa;
+
+ if (event != NETLINK_URELEASE || note->protocol != NETLINK_NETFILTER)
+ return NOTIFY_DONE;
+ /*
+ * Freeing is non-sleeping thanks to kfree_rcu in xt2_table_free.
+ * Is this needed, or do we have a user context in this NL notifier?
+ *
+ * If notifiers are not executed right when they are issued, this
+ * becomes as a race, as a new NL socket could be created with the
+ * same nladdr value (.portid member).
+ */
+ xa = xtnetlink_transact_get(note->net, note->portid);
+ if (xa == NULL)
+ return NOTIFY_DONE;
+ xtnetlink_transact_pop(xa);
+ xtnetlink_transact_free(xa);
+ return NOTIFY_DONE;
+}
+
+static struct notifier_block xtnetlink_nlevent_notifier __read_mostly = {
+ .notifier_call = xtnetlink_nlevent,
+};
+
int __init xtnetlink_init(void)
{
+ int ret;
+
+ INIT_LIST_HEAD(&xtnetlink_transact_list);
+ rwlock_init(&xtnetlink_transact_lock);
+ ret = netlink_register_notifier(&xtnetlink_nlevent_notifier);
+ if (ret < 0)
+ return ret;
return nfnetlink_subsys_register(&xtnetlink_subsys);
}
void __exit xtnetlink_exit(void)
{
nfnetlink_subsys_unregister(&xtnetlink_subsys);
+ netlink_unregister_notifier(&xtnetlink_nlevent_notifier);
+ WARN_ON(!list_empty(&xtnetlink_transact_list));
}
MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_XTABLES);
--
1.7.10.4
--
To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
