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Subject: Re: [PATCH v2] mm/hmm/test: use after free in
 dmirror_allocate_chunk()
To:     Dan Carpenter <dan.carpenter@oracle.com>,
        =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= <jglisse@redhat.com>
CC:     Wei Yongjun <weiyongjun1@huawei.com>,
        Jason Gunthorpe <jgg@ziepe.ca>, <linux-mm@kvack.org>,
        <linux-kernel@vger.kernel.org>, <kernel-janitors@vger.kernel.org>
References: <20200924134651.GA1586456@mwanda>
From:   Ralph Campbell <rcampbell@nvidia.com>
Message-ID: <eb06e0c8-327e-6677-c393-139dffdf0dbe@nvidia.com>
Date:   Thu, 24 Sep 2020 12:25:11 -0700
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On 9/24/20 6:46 AM, Dan Carpenter wrote:
> The error handling code does this:
> 
> err_free:
> 	kfree(devmem);
>          ^^^^^^^^^^^^^
> err_release:
> 	release_mem_region(devmem->pagemap.range.start, range_len(&devmem->pagemap.range));
>                             ^^^^^^^^
> The problem is that when we use "devmem->pagemap.range.start" the
> "devmem" pointer is either NULL or freed.
> 
> Neither the allocation nor the call to request_free_mem_region() has to
> be done under the lock so I moved those to the start of the function.
> 
> Fixes: b2ef9f5a5cb3 ("mm/hmm/test: add selftest driver for HMM")
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>

Looks good.
Reviewed-by: Ralph Campbell <rcampbell@nvidia.com>