Re: [PATCH] netfilter: nf_tables: fix nft_counters_enabled underflow at nf_tables_addchain()

[Pablo Neira Ayuso <pablo@netfilter.org>]

On Mon, Sep 12, 2022 at 09:41:00PM +0900, Tetsuo Handa wrote:
> 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().

Patch LGTM, thanks

> 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")
> ---
>  net/netfilter/nf_tables_api.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
> index 816052089b33..e062754dc6cc 100644
> --- 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;
> -- 
> 2.18.4
>