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

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

[Tetsuo Handa]

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")
---
 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

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

[Pablo Neira Ayuso]

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
> 

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

[Florian Westphal]

Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> 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().

Applied, thanks.