Re: stm class: Prevent user-controllable allocations

[Dan Carpenter]

On Tue, May 07, 2019 at 02:41:13PM +0200, Pavel Machek wrote:
> 
> It seems to me that we still allow overflow if count == ~0. We'll then
> allocate 0 bytes but copy ~0 bytes. That does not sound healthy.
> 
> Fixes: f08b18266c7116e2ec6885dd53a928f580060a71
> 
> Signed-off-by: Pavel Machek <pavel@xxxxxxx>
> 
> diff --git a/drivers/hwtracing/stm/core.c b/drivers/hwtracing/stm/core.c
> index c7ba8ac..8846fca 100644
> --- a/drivers/hwtracing/stm/core.c
> +++ b/drivers/hwtracing/stm/core.c
> @@ -631,7 +631,7 @@ static ssize_t stm_char_write(struct file *file, const char __user *buf,
>  	char *kbuf;
>  	int err;
>  
> -	if (count + 1 > PAGE_SIZE)
> +	if (count > PAGE_SIZE - 1)
>  		count = PAGE_SIZE - 1;

The "count" variable should all be checked in vfs_write().  count + off
is checked in rw_verify_area() and count is capped at MAX_RW_COUNT.

#define MAX_RW_COUNT (INT_MAX & PAGE_MASK)

regards,
dan carpenter