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Date: Wed, 12 Aug 2020 10:57:19 -0700 From: Cong Wang <xiyou.wangcong@...il.com> To: linmiaohe <linmiaohe@...wei.com> Cc: David Miller <davem@...emloft.net>, "kuba@...nel.org" <kuba@...nel.org>, "edumazet@...gle.com" <edumazet@...gle.com>, "kafai@...com" <kafai@...com>, "daniel@...earbox.net" <daniel@...earbox.net>, "jakub@...udflare.com" <jakub@...udflare.com>, "keescook@...omium.org" <keescook@...omium.org>, "zhang.lin16@....com.cn" <zhang.lin16@....com.cn>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] net: Fix potential memory leak in proto_register() On Wed, Aug 12, 2020 at 2:21 AM linmiaohe <linmiaohe@...wei.com> wrote: > > Hi all: > David Miller <davem@...emloft.net> wrote: > >From: Cong Wang <xiyou.wangcong@...il.com> > >Date: Tue, 11 Aug 2020 16:02:51 -0700 > > > >>> @@ -3406,6 +3406,16 @@ static void sock_inuse_add(struct net *net, > >>> int val) } #endif > >>> > >>> +static void tw_prot_cleanup(struct timewait_sock_ops *twsk_prot) { > >>> + if (!twsk_prot) > >>> + return; > >>> + kfree(twsk_prot->twsk_slab_name); > >>> + twsk_prot->twsk_slab_name = NULL; > >>> + kmem_cache_destroy(twsk_prot->twsk_slab); > >> > >> Hmm, are you sure you can free the kmem cache name before > >> kmem_cache_destroy()? To me, it seems kmem_cache_destroy() frees the > >> name via slab_kmem_cache_release() via kfree_const(). > >> With your patch, we have a double-free on the name? > >> > >> Or am I missing anything? > > > >Yep, there is a double free here. > > > >Please fix this. > > Many thanks for both of you to point this issue out. But I'am not really understand, could you please explain it more? > As far as I can see, the double free path is: > 1. kfree(twsk_prot->twsk_slab_name) > 2. kmem_cache_destroy > --> shutdown_memcg_caches > --> shutdown_cache > --> slab_kmem_cache_release > --> kfree_const(s->name) > But twsk_prot->twsk_slab_name is allocated from kasprintf via kmalloc_track_caller while twsk_prot->twsk_slab->name is allocated > via kstrdup_const. So I think twsk_prot->twsk_slab_name and twsk_prot->twsk_slab->name point to different memory, and there is no double free. > You are right. Since it is duplicated, then there is no need to keep ->twsk_slab_name, we can just use twsk_slab->name. I will send a patch to get rid of it. > Or am I missing anything? > > By the way, req_prot_cleanup() do the same things, i.e. free the slab_name before involve kmem_cache_destroy(). If there is a double > free, so as here? Ditto. Can be just removed. Thanks.
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