Return-Path: Date: Tue, 16 Sep 2014 19:38:08 +0200 From: Alexander Aring To: Martin Townsend Cc: Jukka Rissanen , Martin Townsend , linux-zigbee-devel@lists.sourceforge.net, linux-bluetooth@vger.kernel.org, linux-wpan@vger.kernel.org, marcel@holtmann.org Subject: Re: [PATCH v4 bluetooth] 6lowpan: fix incorrect return values in lowpan_rcv Message-ID: <20140916173806.GC6104@omega> References: <20140916121844.GA5349@omega> <54182C6B.6090801@xsilon.com> <20140916123421.GA5576@omega> <54182FB8.4080103@xsilon.com> <20140916124832.GB5576@omega> <1410873619.4860.20.camel@jrissane-mobl.ger.corp.intel.com> <20140916133206.GA6104@omega> <1410875570.4860.23.camel@jrissane-mobl.ger.corp.intel.com> <20140916140459.GB6104@omega> <54184CDB.9050200@xsilon.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 In-Reply-To: <54184CDB.9050200@xsilon.com> List-ID: Hi Martin, On Tue, Sep 16, 2014 at 03:44:43PM +0100, Martin Townsend wrote: > I would like to keep freeing skb's out of process_data as process_data will become something like iphc_decompress_hdr and it would be good if that's all it did. Otherwise I feel we are going to put a constraint on all future header decompression routines in that they must free the skb on error. I think it would be better to defer this so on error you might want to try something else with the skb, maybe not but at least the option is there. > So how about > > struct sk_buff * ret_skb; > switch (skb->data[0] & 0xe0) { > case LOWPAN_DISPATCH_IPHC: /* ipv6 datagram */ > ret_skb = process_data(skb, &hdr); > if (IS_ERR(ret_skb)) > goto drop_skb; > else > skb = ret_skb; > break; > > I know we currently have 3 calls to process_data so it will look fairly ugly in this patch but in my next patch to fix lowpan_rcv to handle uncompressed IPv6 packets that are fragmented there will only be one call to process_data so it won't look so bad. You could even wrap it in a macro but I'm not a fan of this as they can obfuscate the code a bit. > > Thoughts? > sorry, I can't follow how this solve the issue if the "parameter skb" is already consumed or not. If process_data returns a error before parameter consume, then we should run kfree_skb(parameter_skb), if it's afterwards we should do nothing. Point is we don't know that there. I suppose if we do consume_skb and refcount reach 0 the parameter_skb becomes a dangling pointer. - Alex