linux-kernel - Re: [PATCH] IB/rxe: check for allocation failure on elem

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Message-ID: <a43bfb4f-e7c3-f6be-8946-952fb2d4af14@canonical.com>
Date:   Mon, 9 Oct 2017 14:18:46 +0100
From:   Colin Ian King <colin.king@...onical.com>
To:     Doug Ledford <dledford@...hat.com>,
        Leon Romanovsky <leon@...nel.org>
Cc:     Moni Shoua <monis@...lanox.com>, Sean Hefty <sean.hefty@...el.com>,
        Hal Rosenstock <hal.rosenstock@...il.com>,
        linux-rdma@...r.kernel.org, kernel-janitors@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] IB/rxe: check for allocation failure on elem

On 09/10/17 14:16, Doug Ledford wrote:
> On Tue, 2017-09-12 at 17:48 +0300, Leon Romanovsky wrote:
>> On Sat, Sep 09, 2017 at 03:56:07PM +0300, Leon Romanovsky wrote:
>>> On Fri, Sep 08, 2017 at 03:37:45PM +0100, Colin King wrote:
>>>> From: Colin Ian King <colin.king@...onical.com>
>>>>
>>>> The allocation for elem may fail (especially because we're using
>>>> GFP_ATOMIC) so best to check for a null return.  This fixes a
>>>> potential
>>>> null pointer dereference when assigning elem->pool.
>>>>
>>>> Detected by CoverityScan CID#1357507 ("Dereference null return
>>>> value")
>>>>
>>>> Fixes: 8700e3e7c485 ("Soft RoCE driver")
>>>> Signed-off-by: Colin Ian King <colin.king@...onical.com>
>>>> ---
>>>>  drivers/infiniband/sw/rxe/rxe_pool.c | 2 ++
>>>>  1 file changed, 2 insertions(+)
>>>>
>>>> diff --git a/drivers/infiniband/sw/rxe/rxe_pool.c
>>>> b/drivers/infiniband/sw/rxe/rxe_pool.c
>>>> index c1b5f38f31a5..3b4916680018 100644
>>>> --- a/drivers/infiniband/sw/rxe/rxe_pool.c
>>>> +++ b/drivers/infiniband/sw/rxe/rxe_pool.c
>>>> @@ -404,6 +404,8 @@ void *rxe_alloc(struct rxe_pool *pool)
>>>>  	elem = kmem_cache_zalloc(pool_cache(pool),
>>>>  				 (pool->flags & RXE_POOL_ATOMIC)
>>>> ?
>>>>  				 GFP_ATOMIC : GFP_KERNEL);
>>>> +	if (!elem)
>>>> +		return NULL;
>>>>
>>>
>>> It is not enough to simply return NULL, you also should release
>>> "pool" too.
>>
>> Colin,
>> do you plan to fix the comment and resend it?
> 
> Since Colin is non-responsive in this thread, I went ahead and took his
> patch, but then applied a fixup of my own:

Sorry, I somehow missed that email. Thanks for following this up.

> 
> commit a79c0f939da23740c12f43019720055aade89367 (HEAD -> k.o/for-next)
> Author: Doug Ledford <dledford@...hat.com>
> Date:   Mon Oct 9 09:11:32 2017 -0400
> 
>     IB/rxe: put the pool on allocation failure
>     
>     If the allocation of elem fails, it is not sufficient to simply check
>     for NULL and return.  We need to also put our reference on the pool or
>     else we will leave the pool with a permanent ref count and we will never
>     be able to free it.
>     
>     Fixes: 4831ca9e4a8e (IB/rxe: check for allocation failure on elem)
>     Suggested-by: Leon Romanovsky <leon@...nel.org>
>     Signed-off-by: Doug Ledford <dledford@...hat.com>
> 
> diff --git a/drivers/infiniband/sw/rxe/rxe_pool.c b/drivers/infiniband/sw/rxe/rxe_pool.c
> index 3b4916680018..b4a8acc7bb7d 100644
> --- a/drivers/infiniband/sw/rxe/rxe_pool.c
> +++ b/drivers/infiniband/sw/rxe/rxe_pool.c
> @@ -394,23 +394,25 @@ void *rxe_alloc(struct rxe_pool *pool)
>  
>         kref_get(&pool->rxe->ref_cnt);
>  
> -       if (atomic_inc_return(&pool->num_elem) > pool->max_elem) {
> -               atomic_dec(&pool->num_elem);
> -               rxe_dev_put(pool->rxe);
> -               rxe_pool_put(pool);
> -               return NULL;
> -       }
> +       if (atomic_inc_return(&pool->num_elem) > pool->max_elem)
> +               goto out_put_pool;
>  
>         elem = kmem_cache_zalloc(pool_cache(pool),
>                                  (pool->flags & RXE_POOL_ATOMIC) ?
>                                  GFP_ATOMIC : GFP_KERNEL);
>         if (!elem)
> -               return NULL;
> +               goto out_put_pool;
>  
>         elem->pool = pool;
>         kref_init(&elem->ref_cnt);
>  
>         return elem;
> +
> +out_put_pool:
> +       atomic_dec(&pool->num_elem);
> +       rxe_dev_put(pool->rxe);
> +       rxe_pool_put(pool);
> +       return NULL;
>  }
>  
>  void rxe_elem_release(struct kref *kref)
> 
>