linux-kernel - Re: [PATCH V3] staging: r8188eu: Fix unsafe memory access by memcmp.

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Date:   Wed, 6 Apr 2022 16:14:26 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Charlie Sands <sandsch@...thvilleschools.net>
Cc:     gregkh@...uxfoundation.org, Larry.Finger@...inger.net,
        phil@...lpotter.co.uk, linux-staging@...ts.linux.dev,
        linux-kernel@...r.kernel.org, paskripkin@...il.com,
        straube.linux@...il.com, fmdefrancesco@...il.com
Subject: Re: [PATCH V3] staging: r8188eu: Fix unsafe memory access by memcmp.

On Wed, Apr 06, 2022 at 07:25:42AM -0400, Charlie Sands wrote:
> This patch fixes sparse warnings about the memcmp function unsafely accessing 
> userspace memory without first copying it to kernel space.
> 
> Signed-off-by: Charlie Sands <sandsch@...thvilleschools.net>
> ---
> 
> V2: Fixed checkpatch.pl warning and changed variable name as suggested by Greg
> K. H. and improved error checking on the "copy_from_user" function as suggested
> by Pavel Skripkin.
> 
> V3: return -EFAULT from the function when there is a memory error while moving
> it from user space to kernel space and fix incorrect subject from V2
> 
>  drivers/staging/r8188eu/os_dep/ioctl_linux.c | 21 ++++++++++++--------
>  1 file changed, 13 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/staging/r8188eu/os_dep/ioctl_linux.c b/drivers/staging/r8188eu/os_dep/ioctl_linux.c
> index 7df213856d66..9f2182b8e451 100644
> --- a/drivers/staging/r8188eu/os_dep/ioctl_linux.c
> +++ b/drivers/staging/r8188eu/os_dep/ioctl_linux.c
> @@ -3233,23 +3233,28 @@ static int rtw_p2p_get(struct net_device *dev,
>  			       struct iw_request_info *info,
>  			       union iwreq_data *wrqu, char *extra)
>  {
> -	if (!memcmp(wrqu->data.pointer, "status", 6)) {
> +	char wrqu_data[9];
> +
> +	if (copy_from_user(wrqu_data, wrqu->data.pointer, 9) != 0)

How do you know that the user buffer is passing 9 characters long?

You're fixing a real bug, sure, but you've inventing a new API and it's
a rubbish API.  Just delete rtw_p2p_get() and the associated code.  It
has never worked so no one will miss it.

regards,
dan carpenter