Re: [PATCH] net: dsa: fix negative loop bound error on for loop

[Mukesh Ojha]

On 3/31/2019 8:03 PM, Andrew Lunn wrote:
> On Sun, Mar 31, 2019 at 03:25:47PM +0530, Mukesh Ojha wrote:
> > On 3/31/2019 3:12 AM, Colin King wrote:
> > > From: Colin Ian King <colin.king@xxxxxxxxxxxxx>
> > >
> > > Currently the for-loop using an unsigned int for the loop counter
> > > which is problematic when comparing it to the signed int count
> > > This is an issue because if the signed int is negative then
> > > the negative loop bound is implicitly cast to an unsigned int on
> > > the comparison to loop counter i and will yield a very large value,
> > > eventually causing an error when memmove/memcpy'ing outside the
> > > allocated region pointed to by ndata.
> > >
> > > Fix this by simply making the loop counter i a signed int;
> > >
> > > Fixes: f2f2356685bc ("net: dsa: move master ethtool code")
> > > Signed-off-by: Colin Ian King <colin.king@xxxxxxxxxxxxx>
> > > ---
> > >   net/dsa/master.c | 3 +--
> > >   1 file changed, 1 insertion(+), 2 deletions(-)
> > >
> > > diff --git a/net/dsa/master.c b/net/dsa/master.c
> > > index c58f33931be1..1b659647a303 100644
> > > --- a/net/dsa/master.c
> > > +++ b/net/dsa/master.c
> > > @@ -87,8 +87,7 @@ static void dsa_master_get_strings(struct net_device *dev, uint32_t stringset,
> > >   	struct dsa_switch *ds = cpu_dp->ds;
> > >   	int port = cpu_dp->index;
> > >   	int len = ETH_GSTRING_LEN;
> > > -	int mcount = 0, count;
> > > -	unsigned int i;
> > > +	int mcount = 0, count, i;
> > This looks fine but why the return value checking for the negative will not
> > be good here ?
> >  Âcount = ds->ops->get_sset_count(ds, port, stringset);
> Hi Mukesh
>
> Is there a return value check for negative?


Just checked looks like dsa_master_get_sset_count can never return -ve 
value .

Colin,

do we really get this situation in any scenario ?


Thanks.

Mukesh

Mukesh

>     Andrew