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

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Date:   Mon, 1 Apr 2019 11:11:08 +0530
From:   Mukesh Ojha <mojha@...eaurora.org>
To:     Andrew Lunn <andrew@...n.ch>
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 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@...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?


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