Re: [PATCH 4.9 41/51] fib_rules: return 0 directly if an exactly same rule exists when NLM_F_EXCL not supplied

[Florian Westphal]

Nathan Chancellor <natechancellor@xxxxxxxxx> wrote:
> On Wed, May 15, 2019 at 12:56:16PM +0200, Greg Kroah-Hartman wrote:
> > From: Hangbin Liu <liuhangbin@xxxxxxxxx>
> > 
> > [ Upstream commit e9919a24d3022f72bcadc407e73a6ef17093a849 ]

[..]

> > Fixes: 153380ec4b9 ("fib_rules: Added NLM_F_EXCL support to fib_nl_newrule")
> > Reported-by: Thomas Haller <thaller@xxxxxxxxxx>
> > Signed-off-by: Hangbin Liu <liuhangbin@xxxxxxxxx>
> > Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > ---
> >  net/core/fib_rules.c |    6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> > 
> > --- a/net/core/fib_rules.c
> > +++ b/net/core/fib_rules.c
> > @@ -429,9 +429,9 @@ int fib_nl_newrule(struct sk_buff *skb,
> >  	if (rule->l3mdev && rule->table)
> >  		goto errout_free;
> >  
> > -	if ((nlh->nlmsg_flags & NLM_F_EXCL) &&
> > -	    rule_exists(ops, frh, tb, rule)) {
> > -		err = -EEXIST;
> > +	if (rule_exists(ops, frh, tb, rule)) {
> > +		if (nlh->nlmsg_flags & NLM_F_EXCL)
> > +			err = -EEXIST;
> This commit is causing issues on Android devices when Wi-Fi and mobile
> data are both enabled. The device will do a soft reboot consistently.

Not surprising, the patch can't be applied to 4.9 as-is.

In 4.9, code looks like this:

 err = -EINVAL;
 /* irrelevant */
 if (rule_exists(ops, frh, tb, rule)) {
  if (nlh->nlmsg_flags & NLM_F_EXCL)
    err = -EEXIST;
    goto errout_free;
 }

So, if rule_exists() is true, we return -EINVAL to caller
instead of 0, unlike upstream.

I don't think this commit is stable material.