[net] net/ipv6: do not copy DST_NOCOUNT flag on rt init

Message ID 20180913203814.189698-1-posk@google.com
State Changes Requested
Delegated to: David Miller
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Series
  • [net] net/ipv6: do not copy DST_NOCOUNT flag on rt init
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Commit Message

Peter Oskolkov Sept. 13, 2018, 8:38 p.m.
DST_NOCOUNT in dst_entry::flags tracks whether the entry counts
toward route cache size (net->ipv6.sysctl.ip6_rt_max_size).

If the flag is NOT set, dst_ops::pcpuc_entries counter is incremented
in dist_init() and decremented in dst_destroy().

This flag is tied to allocation/deallocation of dst_entry and
should not be copied from another dst/route. Otherwise it can happen
that dst_ops::pcpuc_entries counter grows until no new routes can
be allocated because the counter reached ip6_rt_max_size due to
DST_NOCOUNT not set and thus no counter decrements on gc-ed routes.

Fixes: 3b6761d18bc1 ("net/ipv6: Move dst flags to booleans in fib entries")
Cc: David Ahern <dsahern@gmail.com>
Acked-by: Wei Wang <weiwan@google.com>
Signed-off-by: Peter Oskolkov <posk@google.com>
---
 net/ipv6/route.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

David Ahern Sept. 14, 2018, 4:11 a.m. | #1
On 9/13/18 1:38 PM, Peter Oskolkov wrote:

> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index 3eed045c65a5..a3902f805305 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -946,7 +946,7 @@ static void ip6_rt_init_dst_reject(struct rt6_info *rt, struct fib6_info *ort)
>  
>  static void ip6_rt_init_dst(struct rt6_info *rt, struct fib6_info *ort)
>  {
> -	rt->dst.flags |= fib6_info_dst_flags(ort);
> +	rt->dst.flags |= fib6_info_dst_flags(ort) & ~DST_NOCOUNT;

I think my mistake is setting dst.flags in ip6_rt_init_dst. Flags
argument is passed to ip6_dst_alloc which is always invoked before
ip6_rt_copy_init is called which is the only caller of ip6_rt_init_dst.

>  
>  	if (ort->fib6_flags & RTF_REJECT) {
>  		ip6_rt_init_dst_reject(rt, ort);
>
Peter Oskolkov Sept. 17, 2018, 4:11 p.m. | #2
On Thu, Sep 13, 2018 at 9:11 PM David Ahern <dsahern@gmail.com> wrote:
>
> On 9/13/18 1:38 PM, Peter Oskolkov wrote:
>
> > diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> > index 3eed045c65a5..a3902f805305 100644
> > --- a/net/ipv6/route.c
> > +++ b/net/ipv6/route.c
> > @@ -946,7 +946,7 @@ static void ip6_rt_init_dst_reject(struct rt6_info *rt, struct fib6_info *ort)
> >
> >  static void ip6_rt_init_dst(struct rt6_info *rt, struct fib6_info *ort)
> >  {
> > -     rt->dst.flags |= fib6_info_dst_flags(ort);
> > +     rt->dst.flags |= fib6_info_dst_flags(ort) & ~DST_NOCOUNT;
>
> I think my mistake is setting dst.flags in ip6_rt_init_dst. Flags
> argument is passed to ip6_dst_alloc which is always invoked before
> ip6_rt_copy_init is called which is the only caller of ip6_rt_init_dst.

ip6_rt_cache_alloc calls ip6_dst_alloc with zero as flags; and only
one flag is copied later (DST_HOST) outside of ip6_rt_init_dst().
If the flag assignment is completely removed from ip6_rt_init_dst(),
then DST_NOPOLICY flag will be lost.

Which may be OK, but is more than what this patch tries to solve (do not
copy DST_NOCOUNT flag).

>
> >
> >       if (ort->fib6_flags & RTF_REJECT) {
> >               ip6_rt_init_dst_reject(rt, ort);
> >
>
David Ahern Sept. 17, 2018, 4:13 p.m. | #3
On 9/17/18 9:11 AM, Peter Oskolkov wrote:
> On Thu, Sep 13, 2018 at 9:11 PM David Ahern <dsahern@gmail.com> wrote:
>>
>> On 9/13/18 1:38 PM, Peter Oskolkov wrote:
>>
>>> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
>>> index 3eed045c65a5..a3902f805305 100644
>>> --- a/net/ipv6/route.c
>>> +++ b/net/ipv6/route.c
>>> @@ -946,7 +946,7 @@ static void ip6_rt_init_dst_reject(struct rt6_info *rt, struct fib6_info *ort)
>>>
>>>  static void ip6_rt_init_dst(struct rt6_info *rt, struct fib6_info *ort)
>>>  {
>>> -     rt->dst.flags |= fib6_info_dst_flags(ort);
>>> +     rt->dst.flags |= fib6_info_dst_flags(ort) & ~DST_NOCOUNT;
>>
>> I think my mistake is setting dst.flags in ip6_rt_init_dst. Flags
>> argument is passed to ip6_dst_alloc which is always invoked before
>> ip6_rt_copy_init is called which is the only caller of ip6_rt_init_dst.
> 
> ip6_rt_cache_alloc calls ip6_dst_alloc with zero as flags; and only
> one flag is copied later (DST_HOST) outside of ip6_rt_init_dst().
> If the flag assignment is completely removed from ip6_rt_init_dst(),
> then DST_NOPOLICY flag will be lost.
> 
> Which may be OK, but is more than what this patch tries to solve (do not
> copy DST_NOCOUNT flag).

After 5+ days mostly offline I just started looking at this problem.
Give me some time to chase down a thought I had from my last response.
David Ahern Sept. 17, 2018, 4:59 p.m. | #4
On 9/17/18 9:11 AM, Peter Oskolkov wrote:
> On Thu, Sep 13, 2018 at 9:11 PM David Ahern <dsahern@gmail.com> wrote:
>>
>> On 9/13/18 1:38 PM, Peter Oskolkov wrote:
>>
>>> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
>>> index 3eed045c65a5..a3902f805305 100644
>>> --- a/net/ipv6/route.c
>>> +++ b/net/ipv6/route.c
>>> @@ -946,7 +946,7 @@ static void ip6_rt_init_dst_reject(struct rt6_info *rt, struct fib6_info *ort)
>>>
>>>  static void ip6_rt_init_dst(struct rt6_info *rt, struct fib6_info *ort)
>>>  {
>>> -     rt->dst.flags |= fib6_info_dst_flags(ort);
>>> +     rt->dst.flags |= fib6_info_dst_flags(ort) & ~DST_NOCOUNT;
>>
>> I think my mistake is setting dst.flags in ip6_rt_init_dst. Flags
>> argument is passed to ip6_dst_alloc which is always invoked before
>> ip6_rt_copy_init is called which is the only caller of ip6_rt_init_dst.
> 
> ip6_rt_cache_alloc calls ip6_dst_alloc with zero as flags; and only
> one flag is copied later (DST_HOST) outside of ip6_rt_init_dst().
> If the flag assignment is completely removed from ip6_rt_init_dst(),
> then DST_NOPOLICY flag will be lost.
> 
> Which may be OK, but is more than what this patch tries to solve (do not
> copy DST_NOCOUNT flag).

In the 4.17 kernel (prior to the fib6_info change), ip6_rt_cache_alloc
calls __ip6_dst_alloc with 0 for flags so this is correct. The mistake
is ip6_rt_copy_init -> ip6_rt_init_dst -> fib6_info_dst_flags.

I believe the right fix is to drop the 'rt->dst.flags |=
fib6_info_dst_flags(ort);' from ip6_rt_init_dst.
Peter Oskolkov Sept. 17, 2018, 5:23 p.m. | #5
On Mon, Sep 17, 2018 at 9:59 AM David Ahern <dsahern@gmail.com> wrote:
>
> On 9/17/18 9:11 AM, Peter Oskolkov wrote:
> > On Thu, Sep 13, 2018 at 9:11 PM David Ahern <dsahern@gmail.com> wrote:
> >>
> >> On 9/13/18 1:38 PM, Peter Oskolkov wrote:
> >>
> >>> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> >>> index 3eed045c65a5..a3902f805305 100644
> >>> --- a/net/ipv6/route.c
> >>> +++ b/net/ipv6/route.c
> >>> @@ -946,7 +946,7 @@ static void ip6_rt_init_dst_reject(struct rt6_info *rt, struct fib6_info *ort)
> >>>
> >>>  static void ip6_rt_init_dst(struct rt6_info *rt, struct fib6_info *ort)
> >>>  {
> >>> -     rt->dst.flags |= fib6_info_dst_flags(ort);
> >>> +     rt->dst.flags |= fib6_info_dst_flags(ort) & ~DST_NOCOUNT;
> >>
> >> I think my mistake is setting dst.flags in ip6_rt_init_dst. Flags
> >> argument is passed to ip6_dst_alloc which is always invoked before
> >> ip6_rt_copy_init is called which is the only caller of ip6_rt_init_dst.
> >
> > ip6_rt_cache_alloc calls ip6_dst_alloc with zero as flags; and only
> > one flag is copied later (DST_HOST) outside of ip6_rt_init_dst().
> > If the flag assignment is completely removed from ip6_rt_init_dst(),
> > then DST_NOPOLICY flag will be lost.
> >
> > Which may be OK, but is more than what this patch tries to solve (do not
> > copy DST_NOCOUNT flag).
>
> In the 4.17 kernel (prior to the fib6_info change), ip6_rt_cache_alloc
> calls __ip6_dst_alloc with 0 for flags so this is correct. The mistake
> is ip6_rt_copy_init -> ip6_rt_init_dst -> fib6_info_dst_flags.
>
> I believe the right fix is to drop the 'rt->dst.flags |=
> fib6_info_dst_flags(ort);' from ip6_rt_init_dst.

OK, I sent a v2 with the assignment removed. Thanks for the review!

Patch

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 3eed045c65a5..a3902f805305 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -946,7 +946,7 @@  static void ip6_rt_init_dst_reject(struct rt6_info *rt, struct fib6_info *ort)
 
 static void ip6_rt_init_dst(struct rt6_info *rt, struct fib6_info *ort)
 {
-	rt->dst.flags |= fib6_info_dst_flags(ort);
+	rt->dst.flags |= fib6_info_dst_flags(ort) & ~DST_NOCOUNT;
 
 	if (ort->fib6_flags & RTF_REJECT) {
 		ip6_rt_init_dst_reject(rt, ort);