netdev - Re: [PATCH net] ipv6: fix a dst leak when removing its exception

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Message-ID: <CADvbK_dBExLLRRtft4tF5_gUeshOKoOT5mxnC6+zjpjOoHC8uw@mail.gmail.com>
Date:   Thu, 15 Nov 2018 16:23:38 +0900
From:   Xin Long <lucien.xin@...il.com>
To:     David Ahern <dsa@...ulusnetworks.com>
Cc:     network dev <netdev@...r.kernel.org>, davem <davem@...emloft.net>
Subject: Re: [PATCH net] ipv6: fix a dst leak when removing its exception

On Thu, Nov 15, 2018 at 3:33 PM David Ahern <dsa@...ulusnetworks.com> wrote:
>
> On 11/14/18 11:03 AM, David Ahern wrote:
> > On 11/13/18 8:48 AM, Xin Long wrote:
> >> These is no need to hold dst before calling rt6_remove_exception_rt().
> >> The call to dst_hold_safe() in ip6_link_failure() was for ip6_del_rt(),
> >> which has been removed in Commit 93531c674315 ("net/ipv6: separate
> >> handling of FIB entries from dst based routes"). Otherwise, it will
> >> cause a dst leak.
> >>
> >> This patch is to simply remove the dst_hold_safe() call before calling
> >> rt6_remove_exception_rt() and also do the same in ip6_del_cached_rt().
> >> It's safe, because the removal of the exception that holds its dst's
> >> refcnt is protected by rt6_exception_lock.
> >>
> >> Fixes: 93531c674315 ("net/ipv6: separate handling of FIB entries from dst based routes")
> >> Fixes: 23fb93a4d3f1 ("net/ipv6: Cleanup exception and cache route handling")
> >> Reported-by: Li Shuang <shuali@...hat.com>
> >> Signed-off-by: Xin Long <lucien.xin@...il.com>
> >> ---
> >>  net/ipv6/route.c | 7 +++----
> >>  1 file changed, 3 insertions(+), 4 deletions(-)
> >
> > was this problem actually hit or is this patch based on a code analysis?
> >
>
> I ask because I have not been able to reproduce the leak using existing
> tests (e.g., pmtu) that I know create exceptions.
>
> If this problem was hit, it would be good to get a test case for it.
The attachment is the ip6_dst.sh with IPVS.

# sh ip6_dst.sh

But this one triggers the kernel warnings caused by 2 places:
   unregister_netdevice: waiting for br0 to become free. Usage count = 3

1. one is IPVS, I just posted the fix:
https://patchwork.ozlabs.org/patch/998123/  [1]
2. the other one is IPv6,
ip6_link_failure() will be hit.

So to make this reproduce clearly, you may want to apply
patch [1] firstly.

Download attachment "ip6_dst.sh" of type "application/x-sh" (2734 bytes)