netdev - Re: [iproute PATCH v2 4/5] tc/tc_filter: Make sure filter name is not empty

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Date:   Fri, 18 Aug 2017 13:16:13 +0200
From:   Phil Sutter <phil@....cc>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     Stephen Hemminger <stephen@...workplumber.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [iproute PATCH v2 4/5] tc/tc_filter: Make sure filter name is
 not empty

On Fri, Aug 18, 2017 at 09:30:35AM +0000, David Laight wrote:
> From: Phil Sutter
> > Sent: 17 August 2017 18:10
> > The later check for 'k[0] != 0' requires a non-empty filter name,
> > otherwise NULL pointer dereference in 'q' might happen.
> > 
> > Signed-off-by: Phil Sutter <phil@....cc>
> > ---
> >  tc/tc_filter.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/tc/tc_filter.c b/tc/tc_filter.c
> > index b13fb9185d4fd..a799edb35886d 100644
> > --- a/tc/tc_filter.c
> > +++ b/tc/tc_filter.c
> > @@ -412,6 +412,9 @@ static int tc_filter_get(int cmd, unsigned int flags, int argc, char **argv)
> >  			usage();
> >  			return 0;
> >  		} else {
> > +			if (!strlen(*argv))
> > +				invarg("invalid filter name", *argv);
> 
> That is nearly as bad as:
> 	p[strlen(p)] = 0;

Hey, it's not impossible! I could call tc like so:

| # tc filter get protocol ip prio 1 ""

What's funny about it is that the first call to matches() in
tc_filter_get() will catch the empty last parameter:

| # tc filter get prio 1 protocol ip ""
| Command line is not complete. Try option "help"
| # ./tc/tc filter get prio 1 protocol ip "" ""
| Error: duplicate "priority": "" is the second value.

Cheers, Phil