netfilter: nft_compat: make lists per netns

There are two problems with nft_compat since the netlink config
plane uses a per-netns mutex:

1. Concurrent add/del accesses to the same list
2. accesses to a list element after it has been free'd already.

This patch fixes the first problem.

Freeing occurs from a work queue, after transaction mutexes have been
released, i.e., it still possible for a new transaction (even from
same net ns) to find the to-be-deleted expression in the list.

The ->destroy functions are not allowed to have any such side effects,
i.e. the list_del() in the destroy function is not allowed.

This part of the problem is solved in the next patch.
I tried to make this work by serializing list access via mutex
and by moving list_del() to a deactivate callback, but
Taehee spotted following race on this approach:

  NET #0                          NET #1
   >select_ops()
   ->init()
                                   ->select_ops()
   ->deactivate()
   ->destroy()
      nft_xt_put()
       kfree_rcu(xt, rcu_head);
                                   ->init() <-- use-after-free occurred.

Unfortunately, we can't increment reference count in
select_ops(), because we can't undo the refcount increase in
case a different expression fails in the same batch.

(The destroy hook will only be called in case the expression
 was initialized successfully).

Fixes: f102d66b335a ("netfilter: nf_tables: use dedicated mutex to guard transactions")
Reported-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/net/netfilter/nft_compat.c b/net/netfilter/nft_compat.c
index acc85ac..abed349 100644 (file)
--- a/net/netfilter/nft_compat.c
+++ b/net/netfilter/nft_compat.c
@@ -22,6 +22,7 @@
 #include <linux/netfilter_bridge/ebtables.h>
 #include <linux/netfilter_arp/arp_tables.h>
 #include <net/netfilter/nf_tables.h>
+#include <net/netns/generic.h>
 
 struct nft_xt {
        struct list_head        head;
@@ -43,6 +44,20 @@ struct nft_xt_match_priv {
        void *info;
 };
 
+struct nft_compat_net {
+       struct list_head nft_target_list;
+       struct list_head nft_match_list;
+};
+
+static unsigned int nft_compat_net_id __read_mostly;
+static struct nft_expr_type nft_match_type;
+static struct nft_expr_type nft_target_type;
+
+static struct nft_compat_net *nft_compat_pernet(struct net *net)
+{
+       return net_generic(net, nft_compat_net_id);
+}
+
 static bool nft_xt_put(struct nft_xt *xt)
 {
        if (refcount_dec_and_test(&xt->refcnt)) {
@@ -734,10 +749,6 @@ static const struct nfnetlink_subsystem nfnl_compat_subsys = {
        .cb             = nfnl_nft_compat_cb,
 };
 
-static LIST_HEAD(nft_match_list);
-
-static struct nft_expr_type nft_match_type;
-
 static bool nft_match_cmp(const struct xt_match *match,
                          const char *name, u32 rev, u32 family)
 {
@@ -749,6 +760,7 @@ static const struct nft_expr_ops *
 nft_match_select_ops(const struct nft_ctx *ctx,
                     const struct nlattr * const tb[])
 {
+       struct nft_compat_net *cn;
        struct nft_xt *nft_match;
        struct xt_match *match;
        unsigned int matchsize;
@@ -765,8 +777,10 @@ nft_match_select_ops(const struct nft_ctx *ctx,
        rev = ntohl(nla_get_be32(tb[NFTA_MATCH_REV]));
        family = ctx->family;
 
+       cn = nft_compat_pernet(ctx->net);
+
        /* Re-use the existing match if it's already loaded. */
-       list_for_each_entry(nft_match, &nft_match_list, head) {
+       list_for_each_entry(nft_match, &cn->nft_match_list, head) {
                struct xt_match *match = nft_match->ops.data;
 
                if (nft_match_cmp(match, mt_name, rev, family))
@@ -810,7 +824,7 @@ nft_match_select_ops(const struct nft_ctx *ctx,
 
        nft_match->ops.size = matchsize;
 
-       list_add(&nft_match->head, &nft_match_list);
+       list_add(&nft_match->head, &cn->nft_match_list);
 
        return &nft_match->ops;
 err:
@@ -826,10 +840,6 @@ static struct nft_expr_type nft_match_type __read_mostly = {
        .owner          = THIS_MODULE,
 };
 
-static LIST_HEAD(nft_target_list);
-
-static struct nft_expr_type nft_target_type;
-
 static bool nft_target_cmp(const struct xt_target *tg,
                           const char *name, u32 rev, u32 family)
 {
@@ -841,6 +851,7 @@ static const struct nft_expr_ops *
 nft_target_select_ops(const struct nft_ctx *ctx,
                      const struct nlattr * const tb[])
 {
+       struct nft_compat_net *cn;
        struct nft_xt *nft_target;
        struct xt_target *target;
        char *tg_name;
@@ -861,8 +872,9 @@ nft_target_select_ops(const struct nft_ctx *ctx,
            strcmp(tg_name, "standard") == 0)
                return ERR_PTR(-EINVAL);
 
+       cn = nft_compat_pernet(ctx->net);
        /* Re-use the existing target if it's already loaded. */
-       list_for_each_entry(nft_target, &nft_target_list, head) {
+       list_for_each_entry(nft_target, &cn->nft_target_list, head) {
                struct xt_target *target = nft_target->ops.data;
 
                if (!target->target)
@@ -907,7 +919,7 @@ nft_target_select_ops(const struct nft_ctx *ctx,
        else
                nft_target->ops.eval = nft_target_eval_xt;
 
-       list_add(&nft_target->head, &nft_target_list);
+       list_add(&nft_target->head, &cn->nft_target_list);
 
        return &nft_target->ops;
 err:
@@ -923,13 +935,74 @@ static struct nft_expr_type nft_target_type __read_mostly = {
        .owner          = THIS_MODULE,
 };
 
+static int __net_init nft_compat_init_net(struct net *net)
+{
+       struct nft_compat_net *cn = nft_compat_pernet(net);
+
+       INIT_LIST_HEAD(&cn->nft_target_list);
+       INIT_LIST_HEAD(&cn->nft_match_list);
+
+       return 0;
+}
+
+static void __net_exit nft_compat_exit_net(struct net *net)
+{
+       struct nft_compat_net *cn = nft_compat_pernet(net);
+       struct nft_xt *xt, *next;
+
+       if (list_empty(&cn->nft_match_list) &&
+           list_empty(&cn->nft_target_list))
+               return;
+
+       /* If there was an error that caused nft_xt expr to not be initialized
+        * fully and noone else requested the same expression later, the lists
+        * contain 0-refcount entries that still hold module reference.
+        *
+        * Clean them here.
+        */
+       mutex_lock(&net->nft.commit_mutex);
+       list_for_each_entry_safe(xt, next, &cn->nft_target_list, head) {
+               struct xt_target *target = xt->ops.data;
+
+               list_del_init(&xt->head);
+
+               if (refcount_read(&xt->refcnt))
+                       continue;
+               module_put(target->me);
+               kfree(xt);
+       }
+
+       list_for_each_entry_safe(xt, next, &cn->nft_match_list, head) {
+               struct xt_match *match = xt->ops.data;
+
+               list_del_init(&xt->head);
+
+               if (refcount_read(&xt->refcnt))
+                       continue;
+               module_put(match->me);
+               kfree(xt);
+       }
+       mutex_unlock(&net->nft.commit_mutex);
+}
+
+static struct pernet_operations nft_compat_net_ops = {
+       .init   = nft_compat_init_net,
+       .exit   = nft_compat_exit_net,
+       .id     = &nft_compat_net_id,
+       .size   = sizeof(struct nft_compat_net),
+};
+
 static int __init nft_compat_module_init(void)
 {
        int ret;
 
+       ret = register_pernet_subsys(&nft_compat_net_ops);
+       if (ret < 0)
+               goto err_target;
+
        ret = nft_register_expr(&nft_match_type);
        if (ret < 0)
-               return ret;
+               goto err_pernet;
 
        ret = nft_register_expr(&nft_target_type);
        if (ret < 0)
@@ -942,45 +1015,21 @@ static int __init nft_compat_module_init(void)
        }
 
        return ret;
-
 err_target:
        nft_unregister_expr(&nft_target_type);
 err_match:
        nft_unregister_expr(&nft_match_type);
+err_pernet:
+       unregister_pernet_subsys(&nft_compat_net_ops);
        return ret;
 }
 
 static void __exit nft_compat_module_exit(void)
 {
-       struct nft_xt *xt, *next;
-
-       /* list should be empty here, it can be non-empty only in case there
-        * was an error that caused nft_xt expr to not be initialized fully
-        * and noone else requested the same expression later.
-        *
-        * In this case, the lists contain 0-refcount entries that still
-        * hold module reference.
-        */
-       list_for_each_entry_safe(xt, next, &nft_target_list, head) {
-               struct xt_target *target = xt->ops.data;
-
-               if (WARN_ON_ONCE(refcount_read(&xt->refcnt)))
-                       continue;
-               module_put(target->me);
-               kfree(xt);
-       }
-
-       list_for_each_entry_safe(xt, next, &nft_match_list, head) {
-               struct xt_match *match = xt->ops.data;
-
-               if (WARN_ON_ONCE(refcount_read(&xt->refcnt)))
-                       continue;
-               module_put(match->me);
-               kfree(xt);
-       }
        nfnetlink_subsys_unregister(&nfnl_compat_subsys);
        nft_unregister_expr(&nft_target_type);
        nft_unregister_expr(&nft_match_type);
+       unregister_pernet_subsys(&nft_compat_net_ops);
 }
 
 MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_NFT_COMPAT);