Re: [PATCH v2 nf] netfilter: nf_tables: fix memory leak during stateful obj update

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

On Mon, Feb 21, 2022 at 11:59:22AM +0100, Florian Westphal wrote:
> Florian Westphal <fw@strlen.de> wrote:
> > Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> > > On Sun, Feb 20, 2022 at 12:18:50PM +0100, Florian Westphal wrote:
> > > > stateful objects can be updated from the control plane.
> > > > The transaction logic allocates a temporary object for this purpose.
> > > > 
> > > > This object has to be released via nft_obj_destroy, not kfree, since
> > > > the ->init function was called and it can have side effects beyond
> > > > memory allocation.
> > > > 
> > > > Unlike normal NEWOBJ path, the objects module refcount isn't
> > > > incremented, so add nft_newobj_destroy and use that.
> > > 
> > > Probably this? .udata and .key is NULL for the update path so kfree
> > > should be fine.
> > 
> > Yes, that works too.
> > 
> > We could also ...
> > 
> > > -	module_put(obj->ops->type->owner);
> > > +	/* nf_tables_updobj does not increment module refcount */
> > > +	if (!update)
> > > +		module_put(obj->ops->type->owner);
> > > +
> > 
> > Increment the refcount for update case as well to avoid the special
> > case?

Yes, I also though of this one. I prefer this approach indeed to
consolidate this path.

Would you test and submit v3?

Thanks!

> Untested:
> 
> 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--;