linux-kernel - Re: [PATCH][next] netdevsim: Fix unsigned being compared to less than zero

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Message-ID: <20210604111741.GK1955@kadam>
Date:   Fri, 4 Jun 2021 14:17:41 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Colin King <colin.king@...onical.com>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Dmytro Linkin <dlinkin@...dia.com>,
        Yuval Avnery <yuvalav@...dia.com>,
        Jiri Pirko <jiri@...dia.com>, netdev@...r.kernel.org,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] netdevsim: Fix unsigned being compared to less
 than zero

On Thu, Jun 03, 2021 at 10:56:57PM +0100, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
> 
> The comparison of len < 0 is always false because len is a size_t. Fix
> this by making len a ssize_t instead.
> 
> Addresses-Coverity: ("Unsigned compared against 0")
> Fixes: d395381909a3 ("netdevsim: Add max_vfs to bus_dev")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> ---
>  drivers/net/netdevsim/bus.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/netdevsim/bus.c b/drivers/net/netdevsim/bus.c
> index b56003dfe3cc..ccec29970d5b 100644
> --- a/drivers/net/netdevsim/bus.c
> +++ b/drivers/net/netdevsim/bus.c
> @@ -111,7 +111,7 @@ ssize_t nsim_bus_dev_max_vfs_read(struct file *file,
>  {
>  	struct nsim_bus_dev *nsim_bus_dev = file->private_data;
>  	char buf[11];
> -	size_t len;
> +	ssize_t len;
>  
>  	len = snprintf(buf, sizeof(buf), "%u\n", nsim_bus_dev->max_vfs);
>  	if (len < 0)

The snprintf() in the kernel can't return negatives, but if there isn't
enough space then it returns >= sizeof(buf) so this would lead to an
information leak.  So the right thing to do is change it to scnprintf()
and delete the check if (len < 0) check.

regards,
dan carpenter