ACK: [PATCH 1/1][T/B] infiniband: fix a possible use-after-free bug

[Stefan Bader]

On 20.11.18 02:18, Tyler Hicks wrote:
> From: Cong Wang <xiyou.wangcong at gmail.com>
> 
> ucma_process_join() will free the new allocated "mc" struct,
> if there is any error after that, especially the copy_to_user().
> 
> But in parallel, ucma_leave_multicast() could find this "mc"
> through idr_find() before ucma_process_join() frees it, since it
> is already published.
> 
> So "mc" could be used in ucma_leave_multicast() after it is been
> allocated and freed in ucma_process_join(), since we don't refcnt
> it.
> 
> Fix this by separating "publish" from ID allocation, so that we
> can get an ID first and publish it later after copy_to_user().
> 
> Fixes: c8f6a362bf3e ("RDMA/cma: Add multicast communication support")
> Reported-by: Noam Rathaus <noamr at beyondsecurity.com>
> Signed-off-by: Cong Wang <xiyou.wangcong at gmail.com>
> Signed-off-by: Jason Gunthorpe <jgg at mellanox.com>
> 
> CVE-2018-14734
> 
> (cherry picked from commit cb2595c1393b4a5211534e6f0a0fbad369e21ad8)
> Signed-off-by: Tyler Hicks <tyhicks at canonical.com>
Acked-by: Stefan Bader <stefan.bader at canonical.com>
> ---
>  drivers/infiniband/core/ucma.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/infiniband/core/ucma.c b/drivers/infiniband/core/ucma.c
> index e47baf0950e3..a22b992cde38 100644
> --- a/drivers/infiniband/core/ucma.c
> +++ b/drivers/infiniband/core/ucma.c
> @@ -218,7 +218,7 @@ static struct ucma_multicast* ucma_alloc_multicast(struct ucma_context *ctx)
>  		return NULL;
>  
>  	mutex_lock(&mut);
> -	mc->id = idr_alloc(&multicast_idr, mc, 0, 0, GFP_KERNEL);
> +	mc->id = idr_alloc(&multicast_idr, NULL, 0, 0, GFP_KERNEL);
>  	mutex_unlock(&mut);
>  	if (mc->id < 0)
>  		goto error;
> @@ -1404,6 +1404,10 @@ static ssize_t ucma_process_join(struct ucma_file *file,
>  		goto err3;
>  	}
>  
> +	mutex_lock(&mut);
> +	idr_replace(&multicast_idr, mc, mc->id);
> +	mutex_unlock(&mut);
> +
>  	mutex_unlock(&file->mut);
>  	ucma_put_ctx(ctx);
>  	return 0;
> 


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