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

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Message-ID: <20190331143314.GA20636@lunn.ch>
Date:   Sun, 31 Mar 2019 16:33:14 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Mukesh Ojha <mojha@...eaurora.org>
Cc:     Colin King <colin.king@...onical.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S . Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: dsa: fix negative loop bound error on for loop

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@...onical.com>
> >
> >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@...onical.com>
> >---
> >  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 ?
>  count = ds->ops->get_sset_count(ds, port, stringset);

Hi Mukesh

Is there a return value check for negative?

   Andrew