netdev - Re: [PATCH nf 5/5] netfilter: nf_tables: fix memory leak during stateful obj update

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Message-ID: <20220221205840.08110cab@kicinski-fedora-PC1C0HJN.hsd1.ca.comcast.net>
Date:   Mon, 21 Feb 2022 20:58:40 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Pablo Neira Ayuso <pablo@...filter.org>
Cc:     netfilter-devel@...r.kernel.org, davem@...emloft.net,
        netdev@...r.kernel.org, Florian Westphal <fw@...len.de>
Subject: Re: [PATCH nf 5/5] netfilter: nf_tables: fix memory leak during
 stateful obj update

On Mon, 21 Feb 2022 17:17:57 +0100 Pablo Neira Ayuso wrote:
> From: Florian Westphal <fw@...len.de>
> 
> stateful objects can be updated from the control plane.
> The transaction logic allocates a temporary object for this purpose.
> 
> The ->init function was called for this object, so plain kfree() leaks
> resources. We must call ->destroy function of the object.
> 
> nft_obj_destroy does this, but it also decrements the module refcount,
> but the update path doesn't increment it.
> 
> To avoid special-casing the update object release, do module_get for
> the update case too and release it via nft_obj_destroy().
> 
> Fixes: d62d0ba97b58 ("netfilter: nf_tables: Introduce stateful object update operation")
> Cc: Fernando Fernandez Mancera <ffmancera@...eup.net>
> Signed-off-by: Florian Westphal <fw@...len.de>
> Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
> ---
>  net/netfilter/nf_tables_api.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
> index 3081c4399f10..49060f281342 100644
> --- a/net/netfilter/nf_tables_api.c
> +++ b/net/netfilter/nf_tables_api.c
> @@ -6553,10 +6553,13 @@ static int nf_tables_updobj(const struct nft_ctx *ctx,
>  	struct nft_trans *trans;
>  	int err;
>  
> +	if (!try_module_get(type->owner))
> +		return -ENOENT;
> +
>  	trans = nft_trans_alloc(ctx, NFT_MSG_NEWOBJ,
>  				sizeof(struct nft_trans_obj));
>  	if (!trans)
> -		return -ENOMEM;
> +		goto err_trans;
>  
>  	newobj = nft_obj_init(ctx, type, attr);
>  	if (IS_ERR(newobj)) {
> @@ -6573,6 +6576,8 @@ static int nf_tables_updobj(const struct nft_ctx *ctx,
>  
>  err_free_trans:
>  	kfree(trans);
> +err_trans:
> +	module_put(type->owner);
>  	return err;
>  }
>  
> @@ -8185,7 +8190,7 @@ static void nft_obj_commit_update(struct nft_trans *trans)
>  	if (obj->ops->update)
>  		obj->ops->update(obj, newobj);
>  
> -	kfree(newobj);
> +	nft_obj_destroy(&trans->ctx, newobj);
>  }
>  
>  static void nft_commit_release(struct nft_trans *trans)
> @@ -8976,7 +8981,7 @@ static int __nf_tables_abort(struct net *net, enum nfnl_abort_action action)
>  			break;
>  		case NFT_MSG_NEWOBJ:
>  			if (nft_trans_obj_update(trans)) {
> -				kfree(nft_trans_obj_newobj(trans));
> +				nft_obj_destroy(&trans->ctx, nft_trans_obj_newobj(trans));
>  				nft_trans_destroy(trans);
>  			} else {
>  				trans->ctx.table->use--;

net/netfilter/nf_tables_api.c:6561:6: warning: variable 'err' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
        if (!trans)
            ^~~~~~
net/netfilter/nf_tables_api.c:6581:9: note: uninitialized use occurs here
        return err;
               ^~~
net/netfilter/nf_tables_api.c:6561:2: note: remove the 'if' if its condition is always false
        if (!trans)
        ^~~~~~~~~~~
net/netfilter/nf_tables_api.c:6554:9: note: initialize the variable 'err' to silence this warning
        int err;
               ^
                = 0