ACK: [Precise] arm: oabi compat: add missing access checks

[Tim Gardner]

On 08/26/2016 03:22 AM, Luis Henriques wrote:
> From: Dave Weinstein <olorin at google.com>
> 
> Add access checks to sys_oabi_epoll_wait() and sys_oabi_semtimedop().
> This fixes CVE-2016-3857, a local privilege escalation under
> CONFIG_OABI_COMPAT.
> 
> Cc: stable at vger.kernel.org
> Reported-by: Chiachih Wu <wuchiachih at gmail.com>
> Reviewed-by: Kees Cook <keescook at chromium.org>
> Reviewed-by: Nicolas Pitre <nico at linaro.org>
> Signed-off-by: Dave Weinstein <olorin at google.com>
> Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
> 
> CVE-2016-3857
> Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
> ---
>  arch/arm/kernel/sys_oabi-compat.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/kernel/sys_oabi-compat.c b/arch/arm/kernel/sys_oabi-compat.c
> index af0aaebf4de6..32884a6006cf 100644
> --- a/arch/arm/kernel/sys_oabi-compat.c
> +++ b/arch/arm/kernel/sys_oabi-compat.c
> @@ -275,8 +275,12 @@ asmlinkage long sys_oabi_epoll_wait(int epfd,
>  	mm_segment_t fs;
>  	long ret, err, i;
>  
> -	if (maxevents <= 0 || maxevents > (INT_MAX/sizeof(struct epoll_event)))
> +	if (maxevents <= 0 ||
> +			maxevents > (INT_MAX/sizeof(*kbuf)) ||
> +			maxevents > (INT_MAX/sizeof(*events)))
>  		return -EINVAL;
> +	if (!access_ok(VERIFY_WRITE, events, sizeof(*events) * maxevents))
> +		return -EFAULT;
>  	kbuf = kmalloc(sizeof(*kbuf) * maxevents, GFP_KERNEL);
>  	if (!kbuf)
>  		return -ENOMEM;
> @@ -313,6 +317,8 @@ asmlinkage long sys_oabi_semtimedop(int semid,
>  
>  	if (nsops < 1 || nsops > SEMOPM)
>  		return -EINVAL;
> +	if (!access_ok(VERIFY_READ, tsops, sizeof(*tsops) * nsops))
> +		return -EFAULT;
>  	sops = kmalloc(sizeof(*sops) * nsops, GFP_KERNEL);
>  	if (!sops)
>  		return -ENOMEM;
> 

This is a clean cherry-pick of 7de249964f5578e67b99699c5f0b405738d820a2
('arm: oabi compat: add missing access checks') though that is not noted
in the commit log.

-- 
Tim Gardner tim.gardner at canonical.com