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Mon, 23 Jul 2018 11:36:56 +0200 (CEST) Date: Mon, 23 Jul 2018 11:38:55 +0200 X-SMTPAUTHUS: auth mail.us.es From: Pablo Neira Ayuso To: Florian Westphal Cc: David Miller , cscnull@gmail.com, kadlec@blackhole.kfki.hu, johannes.berg@intel.com, Jason@zx2c4.com, ktkhai@virtuozzo.com, lucien.xin@gmail.com, xiyou.wangcong@gmail.com, dsahern@gmail.com, netfilter-devel@vger.kernel.org, tom@quantonium.net, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] netlink: fix memory leak of dump Message-ID: <20180723093855.c4ncixsnkee6r34v@salvia> References: <20180722143354.23722-1-cscnull@gmail.com> <20180722163925.gdfkndldatsoae6x@breakpoint.cc> <20180722.100755.19840167505550163.davem@davemloft.net> <20180722180910.wcwhantwpm2nfxet@breakpoint.cc> <20180723091551.mwhltw4ujm4bylvj@salvia> <20180723092818.ztsfsnqzxgzrauim@breakpoint.cc> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180723092818.ztsfsnqzxgzrauim@breakpoint.cc> User-Agent: NeoMutt/20170113 (1.7.2) X-Virus-Scanned: ClamAV using ClamSMTP Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 23, 2018 at 11:28:18AM +0200, Florian Westphal wrote: > Pablo Neira Ayuso wrote: > > > diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c > > > --- a/net/netfilter/nf_tables_api.c > > > +++ b/net/netfilter/nf_tables_api.c > > > @@ -5010,6 +5013,22 @@ nft_obj_filter_alloc(const struct nlattr * const nla[]) > > > return filter; > > > } > > > > > > +static int nf_tables_dump_obj_start(struct netlink_callback *cb) > > > +{ > > > + const struct nlattr * const *nla = cb->data; > > On-Stack input. > I can't see how its wrong, ->start() happens from same context as > netlink_dump_start so its valid. > > > > + struct nft_obj_filter *filter = NULL; > > > + > > > + if (nla[NFTA_OBJ_TABLE] || > > > + nla[NFTA_OBJ_TYPE]) { > > > + filter = nft_obj_filter_alloc(nla); > > > + if (IS_ERR(filter)) > > > + return -ENOMEM; > > > + } > > > + > > > + cb->data = filter; > > And this replaced the on-stack input with dynamically > allocated one, which will be free'd via ->done(). > > > > /* called with rcu_read_lock held */ > > > static int nf_tables_getobj(struct net *net, struct sock *nlsk, > > > struct sk_buff *skb, const struct nlmsghdr *nlh, > > > @@ -5028,21 +5047,13 @@ static int nf_tables_getobj(struct net *net, struct sock *nlsk, > > > > > > if (nlh->nlmsg_flags & NLM_F_DUMP) { > > > struct netlink_dump_control c = { > > > + .start = nf_tables_dump_obj_start, > > > .dump = nf_tables_dump_obj, > > > .done = nf_tables_dump_obj_done, > > > .module = THIS_MODULE, > > > + .data = (void *)nla, > > > > You cannot do this. > > > > nla is allocated in this stack. > > Yes. > > > the nla will not be available in the second recv(), it won't be there. > > Its replaced in ->start(). > > As David pointed out, once ->start() returns 0 we set cb_running, i.e. > only after successful ->start() netlink core will call ->dump() again. > > So I see no problem setting ->data to onstack cookie and then > duplicating it to heap via kmemdup in ->start(). > > As far as I can see netlink core offers all functionality already, > so we only need to switch netfilter to make use of it. > > If you disagree please let me know, otherwise I will cook up > a patch along this pattern for net/netfilter/*. Why not just call ->done from netlink_dump_start() when it fails?