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Date: Wed, 12 Aug 2020 09:21:36 +0000 From: linmiaohe <linmiaohe@...wei.com> To: David Miller <davem@...emloft.net>, "xiyou.wangcong@...il.com" <xiyou.wangcong@...il.com> CC: "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() 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. 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? Thanks.
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