From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [PATCH net-next 2/2] net/ipv6: Fix missing rcu dereferences on from Date: Tue, 24 Apr 2018 08:56:17 -0700 Message-ID: References: <20180423183207.9124-1-dsahern@gmail.com> <20180423183207.9124-3-dsahern@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit To: David Ahern , netdev@vger.kernel.org Return-path: Received: from mail-pg0-f65.google.com ([74.125.83.65]:36066 "EHLO mail-pg0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751760AbeDXP4U (ORCPT ); Tue, 24 Apr 2018 11:56:20 -0400 Received: by mail-pg0-f65.google.com with SMTP id i6so11190138pgv.3 for ; Tue, 24 Apr 2018 08:56:19 -0700 (PDT) In-Reply-To: Content-Language: en-US Sender: netdev-owner@vger.kernel.org List-ID: On 04/24/2018 08:54 AM, Eric Dumazet wrote: > > > On 04/23/2018 11:32 AM, David Ahern wrote: >> kbuild test robot reported 2 uses of rt->from not properly accessed >> using rcu_dereference: >> 1. add rcu_dereference_protected to rt6_remove_exception_rt and make >> sure it is always called with rcu lock held. >> >> 2. change rt6_do_redirect to take a reference on 'from' when accessed >> the first time so it can be used the sceond time outside of the lock >> >> Fixes: a68886a69180 ("net/ipv6: Make from in rt6_info rcu protected") >> Reported-by: kbuild test robot >> Signed-off-by: David Ahern >> --- >> net/ipv6/route.c | 15 ++++++++++----- >> 1 file changed, 10 insertions(+), 5 deletions(-) >> >> diff --git a/net/ipv6/route.c b/net/ipv6/route.c >> index 354a5b8d016f..ac3e51631c65 100644 >> --- a/net/ipv6/route.c >> +++ b/net/ipv6/route.c >> @@ -1541,11 +1541,13 @@ static struct rt6_info *rt6_find_cached_rt(struct fib6_info *rt, >> static int rt6_remove_exception_rt(struct rt6_info *rt) >> { >> struct rt6_exception_bucket *bucket; >> - struct fib6_info *from = rt->from; >> struct in6_addr *src_key = NULL; >> struct rt6_exception *rt6_ex; >> + struct fib6_info *from; >> int err; >> >> + from = rcu_dereference_protected(rt->from, >> + lockdep_is_held(&rt6_exception_lock)); > > This does not make any sense. > > We lock rt6_exception_lock a bit later in this function (line 1558) > > If we really were holding rt6_exception_lock here we would dead lock. I will send this fix : diff --git a/net/ipv6/route.c b/net/ipv6/route.c index ac3e51631c659b5c5c8a93c17011cb7f3ad266e2..432c4bcc1111085671f32987e4673e47898085a3 100644 --- a/net/ipv6/route.c +++ b/net/ipv6/route.c @@ -1546,8 +1546,7 @@ static int rt6_remove_exception_rt(struct rt6_info *rt) struct fib6_info *from; int err; - from = rcu_dereference_protected(rt->from, - lockdep_is_held(&rt6_exception_lock)); + from = rcu_dereference(rt->from); if (!from || !(rt->rt6i_flags & RTF_CACHE)) return -EINVAL;