[PATCH] cxl: Check if afu is not null in cxl_slbia

[Michael Neuling]

On Fri, 2015-07-10 at 09:04 +1000, Daniel Axtens wrote:
> The pointer to an AFU in the adapter's list of AFUs can be null
> if we're in the process of removing AFUs. The afu_list_lock
> doesn't guard against this.
> 
> Say we have 2 slices, and we're in the process of removing cxl.
>  - We remove the AFUs in order (see cxl_remove). In cxl_remove_afu
>    for AFU 0, we take the lock, set adapter->afu[0] = NULL, and
>    release the lock.
>  - Then we get an slbia. In cxl_slbia we take the lock, and set
>    afu = adapter->afu[0], which is NULL.
>  - Therefore our attempt to check afu->enabled will blow up.
> 
> Therefore, check if afu is a null pointer before dereferencing it.
> 
> cc: STABLE

FYI This needs to be (see Documentation/stable_kernel_rules.txt):
Cc: stable at vger.kernel.org

Other than that, looks good.  Thanks.

Acked-by: Michael Neuling <mikey at neuling.org>

> Signed-off-by: Daniel Axtens <dja at axtens.net>
> ---
>  drivers/misc/cxl/main.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/misc/cxl/main.c b/drivers/misc/cxl/main.c
> index 11a2044d6b0f..5bcd676bfd59 100644
> --- a/drivers/misc/cxl/main.c
> +++ b/drivers/misc/cxl/main.c
> @@ -86,7 +86,7 @@ static inline void cxl_slbia_core(struct mm_struct *mm)
>  		spin_lock(&adapter->afu_list_lock);
>  		for (slice = 0; slice < adapter->slices; slice++) {
>  			afu = adapter->afu[slice];
> -			if (!afu->enabled)
> +			if (!afu || !afu->enabled)
>  				continue;
>  			rcu_read_lock();
>  			idr_for_each_entry(&afu->contexts_idr, ctx, id)