Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755937AbcJUQbY (ORCPT ); Fri, 21 Oct 2016 12:31:24 -0400 Received: from mail-wm0-f67.google.com ([74.125.82.67]:33771 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752432AbcJUQbV (ORCPT ); Fri, 21 Oct 2016 12:31:21 -0400 Date: Fri, 21 Oct 2016 18:31:18 +0200 From: Jiri Pirko To: Arnd Bergmann Cc: "David S. Miller" , Alexander Duyck , Tom Herbert , Jiri Pirko , Hadar Hen Zion , Gao Feng , Eric Garver , Amir Vadai , netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] flow_dissector: avoid uninitialized variable access Message-ID: <20161021163118.GA2155@nanopsycho.orion> References: <20161021155626.4020344-1-arnd@arndb.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161021155626.4020344-1-arnd@arndb.de> User-Agent: Mutt/1.7.0 (2016-08-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1759 Lines: 51 Fri, Oct 21, 2016 at 05:55:53PM CEST, arnd@arndb.de wrote: >gcc warns about an uninitialized pointer dereference in the vlan >priority handling: > >net/core/flow_dissector.c: In function '__skb_flow_dissect': >net/core/flow_dissector.c:281:61: error: 'vlan' may be used uninitialized in this function [-Werror=maybe-uninitialized] > >From all I can tell, this warning is about a real bug, and we >should not attempt look up the vlan header if there was >no vlan tag. I don't see how vlan could be used uninitialized. But I understand that this is impossible for gcc to track it. Please just use uninitialized_var() > >Fixes: f6a66927692e ("flow_dissector: Get vlan priority in addition to vlan id") >Signed-off-by: Arnd Bergmann >--- >I'm not sure about this one, please have a closer look at what >the original code does before applying. >--- > net/core/flow_dissector.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > >diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c >index 44e6ba9d3a6b..dd6003bf27e1 100644 >--- a/net/core/flow_dissector.c >+++ b/net/core/flow_dissector.c >@@ -245,7 +245,7 @@ bool __skb_flow_dissect(const struct sk_buff *skb, > } > case htons(ETH_P_8021AD): > case htons(ETH_P_8021Q): { >- const struct vlan_hdr *vlan; >+ const struct vlan_hdr *vlan = NULL; > > if (skb && skb_vlan_tag_present(skb)) > proto = skb->protocol; >@@ -264,7 +264,7 @@ bool __skb_flow_dissect(const struct sk_buff *skb, > } > > skip_vlan = true; >- if (dissector_uses_key(flow_dissector, >+ if (vlan && dissector_uses_key(flow_dissector, > FLOW_DISSECTOR_KEY_VLAN)) { > key_vlan = skb_flow_dissector_target(flow_dissector, > FLOW_DISSECTOR_KEY_VLAN, >-- >2.9.0 >