Re: [PATCH V2] Fix unsafe memory access by memcmp

[Dan Carpenter]

On Sun, Apr 03, 2022 at 10:52:07PM -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@xxxxxxxxxxxxxxxxxxxxx>
> ---
> 
> 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.
> 
>  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..4b4eec2bde96 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)
> +		return 0;

return -EFAULT;  We can't assume that that user wants to copy 9 bytes
especially when they're passing a 4 character + NUL string.

This is a custom ioctl.  Called from ioctl_private_iw_point().

I think if you try to dereference a user pointer like this then it will
cause a crash, right?  So that means no one has ever tested or used this
code and we hopefully we can just delete it?

regards,
dan carpenter