netfilter: nf_tables: Don't allocate nft_rule_dump_ctx

Since struct netlink_callback::args is not used by rule dumpers anymore,
use it to hold nft_rule_dump_ctx. Add a build-time check to make sure it
won't ever exceed the available space.

Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Florian Westphal <fw@strlen.de>

diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
index a2e6c826bd0897b88581ba87d1aaf3fc5d9fefaf..68321345bb6db4cccd6a3927407e04d83559b2a8 100644 (file)
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -3453,7 +3453,7 @@ static int __nf_tables_dump_rules(struct sk_buff *skb,
                                  const struct nft_table *table,
                                  const struct nft_chain *chain)
 {
-       struct nft_rule_dump_ctx *ctx = cb->data;
+       struct nft_rule_dump_ctx *ctx = (void *)cb->ctx;
        struct net *net = sock_net(skb->sk);
        const struct nft_rule *rule, *prule;
        unsigned int entries = 0;
@@ -3498,7 +3498,7 @@ static int nf_tables_dump_rules(struct sk_buff *skb,
                                struct netlink_callback *cb)
 {
        const struct nfgenmsg *nfmsg = nlmsg_data(cb->nlh);
-       struct nft_rule_dump_ctx *ctx = cb->data;
+       struct nft_rule_dump_ctx *ctx = (void *)cb->ctx;
        struct nft_table *table;
        const struct nft_chain *chain;
        unsigned int idx = 0;
@@ -3553,42 +3553,35 @@ done:
 
 static int nf_tables_dump_rules_start(struct netlink_callback *cb)
 {
+       struct nft_rule_dump_ctx *ctx = (void *)cb->ctx;
        const struct nlattr * const *nla = cb->data;
-       struct nft_rule_dump_ctx *ctx = NULL;
 
-       ctx = kzalloc(sizeof(*ctx), GFP_ATOMIC);
-       if (!ctx)
-               return -ENOMEM;
+       BUILD_BUG_ON(sizeof(*ctx) > sizeof(cb->ctx));
 
        if (nla[NFTA_RULE_TABLE]) {
                ctx->table = nla_strdup(nla[NFTA_RULE_TABLE], GFP_ATOMIC);
-               if (!ctx->table) {
-                       kfree(ctx);
+               if (!ctx->table)
                        return -ENOMEM;
-               }
        }
        if (nla[NFTA_RULE_CHAIN]) {
                ctx->chain = nla_strdup(nla[NFTA_RULE_CHAIN], GFP_ATOMIC);
                if (!ctx->chain) {
                        kfree(ctx->table);
-                       kfree(ctx);
                        return -ENOMEM;
                }
        }
        if (NFNL_MSG_TYPE(cb->nlh->nlmsg_type) == NFT_MSG_GETRULE_RESET)
                ctx->reset = true;
 
-       cb->data = ctx;
        return 0;
 }
 
 static int nf_tables_dump_rules_done(struct netlink_callback *cb)
 {
-       struct nft_rule_dump_ctx *ctx = cb->data;
+       struct nft_rule_dump_ctx *ctx = (void *)cb->ctx;
 
        kfree(ctx->table);
        kfree(ctx->chain);
-       kfree(ctx);
        return 0;
 }