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

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Message-ID: <3723042a-88db-fa87-02ec-4ff231bbaff2@codeaurora.org>
Date:   Sun, 31 Mar 2019 15:25:47 +0530
From:   Mukesh Ojha <mojha@...eaurora.org>
To:     Colin King <colin.king@...onical.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S . Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Cc:     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 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);


Cheers,
Mukesh


>   	uint8_t pfx[4];
>   	uint8_t *ndata;
>