netfilter: nf_tables: fix nft_counters_enabled underflow at nf_tables_addchain()

[ Upstream commit 921ebde3c0d22c8cba74ce8eb3cc4626abff1ccd ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
index d35d09df83fee67c9adc4184b51b014acb7e8d16..d8e66467c06c02c7440ffd09d68321fb7c996f27 100644 (file)
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -2103,7 +2103,6 @@ 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;
@@ -2117,6 +2116,7 @@ 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)
@@ -2150,6 +2150,8 @@ 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;
@@ -2224,9 +2226,6 @@ 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;