Re: [PATCH] drivers: char: mem: Fix thinko in kmem address checks

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Jan 04, 2017 at 11:37:49AM +0000, Robin Murphy wrote:
> When borrowing the pfn_valid() check from mmap_kmem(), somebody managed

"sombody"?  :)

> to get physical and virtual addresses spectacularly muddled up, such
> that we've ended up with checks for one being the other. Whilst this
> does indeed prevent out-of-bounds accesses crashing, on most systems it
> also prevents the more desirable use-case of working at all ever.
> 
> Check the *virtual* offset correctly for what it is.
> 
> Reported-by: Jason A. Donenfeld <Jason@zx2c4.com>
> CC: stable@vger.kernel.org
> Fixes: 148a1bc84398 ("drivers: char: mem: Check {read,write}_kmem() addresses")
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> ---
>  drivers/char/mem.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/char/mem.c b/drivers/char/mem.c
> index 5bb1985ec484..bdc6a4018604 100644
> --- a/drivers/char/mem.c
> +++ b/drivers/char/mem.c
> @@ -381,7 +381,7 @@ static ssize_t read_kmem(struct file *file, char __user *buf,
>  	char *kbuf; /* k-addr because vread() takes vmlist_lock rwlock */
>  	int err = 0;
>  
> -	if (!pfn_valid(PFN_DOWN(p)))
> +	if (!virt_addr_valid(p))
>  		return -EIO;
>  
>  	read = 0;
> @@ -512,7 +512,7 @@ static ssize_t write_kmem(struct file *file, const char __user *buf,
>  	char *kbuf; /* k-addr because vwrite() takes vmlist_lock rwlock */
>  	int err = 0;
>  
> -	if (!pfn_valid(PFN_DOWN(p)))
> +	if (!virt_addr_valid(p))
>  		return -EIO;
>  
>  	if (p < (unsigned long) high_memory) {

Jason, can you verify this fixes your test case?

thanks,

greg k-h