Re: [PATCH] device-dax: fix cdev leak

From	Dan Williams <dan.j.williams@intel.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] device-dax: fix cdev leak
Date	2017-02-23 21:30 +0100
Message-ID	<te8bv-6hU-1@gated-at.bofh.it> (permalink)
References	<te7fs-5FA-7@gated-at.bofh.it> <te8bv-6hU-3@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Thu, Feb 23, 2017 at 12:20 PM, Jason Gunthorpe
<jgunthorpe@obsidianresearch.com> wrote:
> On Thu, Feb 23, 2017 at 11:22:03AM -0800, Dan Williams wrote:
>> If device_add() fails, cleanup the cdev. Otherwise, we leak a kobj_map()
>> with a stale device number.
>>
>> Fixes: ba09c01d2fa8 ("dax: convert to the cdev api")
>> Cc: <stable@vger.kernel.org>
>> Cc: Logan Gunthorpe <logang@deltatee.com>
>> Reported-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
>> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
>>  drivers/dax/dax.c |    1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/dax/dax.c b/drivers/dax/dax.c
>> index ed758b74ddf0..0f8008dd0b0c 100644
>> +++ b/drivers/dax/dax.c
>> @@ -724,6 +724,7 @@ struct dax_dev *devm_create_dax_dev(struct dax_region *dax_region,
>>       dev_set_name(dev, "dax%d.%d", dax_region->id, dax_dev->id);
>>       rc = device_add(dev);
>>       if (rc) {
>> +             cdev_del(&dax_dev->cdev);
>
> This probably should call into unregister_dax_dev and just skip the
> device_unregister part.
>
> Once cdev_add returns it is possible for a mmap to have been created,
> so cleanup after that point has to go through all the other
> unregister_dax_dev steps.

Ah true. I was thinking the device node is not auto-created if the
device_add() fails, but there's theoretically nothing stopping
userspace from trying to hit this race with its own self-created
device-node.

Thread

[PATCH] device-dax: fix cdev leak Dan Williams <dan.j.williams@intel.com> - 2017-02-23 20:30 +0100
  Re: [PATCH] device-dax: fix cdev leak Dan Williams <dan.j.williams@intel.com> - 2017-02-23 21:30 +0100
  Re: [PATCH] device-dax: fix cdev leak Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2017-02-23 21:30 +0100

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