netfilter: nf_tables: fix nft_counters_enabled underflow at nf_tables_addchain()

syzbot is reporting underflow of nft_counters_enabled counter at
nf_tables_addchain() [1], for commit 43eb8949cfdffa76 ("netfilter:
nf_tables: do not leave chain stats enabled on error") missed that
nf_tables_chain_destroy() after nft_basechain_init() in the error path of
nf_tables_addchain() decrements the counter because nft_basechain_init()
makes nft_is_base_chain() return true by setting NFT_CHAIN_BASE flag.

Increment the counter immediately after returning from
nft_basechain_init().

Link:  https://syzkaller.appspot.com/bug?extid=b5d82a651b71cd8a75ab [1]
Reported-by: syzbot <syzbot+b5d82a651b71cd8a75ab@syzkaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Tested-by: syzbot <syzbot+b5d82a651b71cd8a75ab@syzkaller.appspotmail.com>
Fixes: 43eb8949cfdffa76 ("netfilter: nf_tables: do not leave chain stats enabled on error")
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 816052089b336edabca19e38504ae4204d20f4aa..e062754dc6ccb53b98a95a89504d7019f72a3d0d 100644 (file)
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -2197,7 +2197,6 @@ static int nf_tables_addchain(struct nft_ctx *ctx, u8 family, u8 genmask,
                              struct netlink_ext_ack *extack)
 {
        const struct nlattr * const *nla = ctx->nla;
-       struct nft_stats __percpu *stats = NULL;
        struct nft_table *table = ctx->table;
        struct nft_base_chain *basechain;
        struct net *net = ctx->net;
@@ -2212,6 +2211,7 @@ static int nf_tables_addchain(struct nft_ctx *ctx, u8 family, u8 genmask,
                return -EOVERFLOW;
 
        if (nla[NFTA_CHAIN_HOOK]) {
+               struct nft_stats __percpu *stats = NULL;
                struct nft_chain_hook hook;
 
                if (flags & NFT_CHAIN_BINDING)
@@ -2245,6 +2245,8 @@ static int nf_tables_addchain(struct nft_ctx *ctx, u8 family, u8 genmask,
                        kfree(basechain);
                        return err;
                }
+               if (stats)
+                       static_branch_inc(&nft_counters_enabled);
        } else {
                if (flags & NFT_CHAIN_BASE)
                        return -EINVAL;
@@ -2319,9 +2321,6 @@ static int nf_tables_addchain(struct nft_ctx *ctx, u8 family, u8 genmask,
                goto err_unregister_hook;
        }
 
-       if (stats)
-               static_branch_inc(&nft_counters_enabled);
-
        table->use++;
 
        return 0;