Re: [PATCH 07/14] infiniband: utilize new device_add_cdev helper function

Jason Gunthorpe
2017-02-21T19:09:05Z

On Mon, Feb 20, 2017 at 10:00:46PM -0700, Logan Gunthorpe wrote:
> This patch updates core/ucm.c which didn't originally use the
> cdev.kobj.parent with it's parent device. I did not look heavily into
> whether this was a bug or not, but it seems likely to me there would
> be a use before free.

Hum, is probably safe - ib_ucm_remove_one can only happen on module
unload and the cdev holds the module lock while open.

Even so device_add_cdev should be used anyhow.

> I also took a look at core/uverbs_main.c, core/user_mad.c and
> hw/hfi1/device.c which utilize cdev.kobj.parent but because the
> infiniband core seems to use kobjs internally instead of struct devices
> they could not be converted to use the new helper API and still
> directly manipulate the internals of the kobj.

Yes, and hfi1 had the same use-afte-free bug when it was first
submitted as well. IHMO cdev should have a helper entry for this style
of use case as well.

> diff --git a/drivers/infiniband/core/ucm.c b/drivers/infiniband/core/ucm.c
> index e0a995b..38ea316 100644
> +++ b/drivers/infiniband/core/ucm.c
> @@ -1283,18 +1283,20 @@ static void ib_ucm_add_one(struct ib_device *device)
> set_bit(devnum, dev_map);
> }
>
> + device_initialize(&ucm_dev->dev);

Ah, this needs more help. Once device_initialize is called put_device
should be the error-unwind, can you use something more like this?

>From ac7a35ea98066c9a9e3f3e54557c0ccda44b0ffc Mon Sep 17 00:00:00 2001
From: Jason Gunthorpe <jgunthorpe-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>
Date: Tue, 21 Feb 2017 12:07:55 -0700
Subject: [PATCH] infiniband: utilize new device_add_cdev helper

The use after free is not triggerable here because the cdev holds
the module lock and the only device_unregister is only triggered by
module ouload, however make the change for consistency.

To make this work the cdev_del needs to move out of the struct device
release function.

Signed-off-by: Jason Gunthorpe <jgunthorpe-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>
---
drivers/infiniband/core/ucm.c | 25 ++++++++++++++-----------
1 file changed, 14 insertions(+), 11 deletions(-)

diff --git a/drivers/infiniband/core/ucm.c b/drivers/infiniband/core/ucm.c
index 7713ef089c3ccc..acda8d941381f3 100644
--- a/drivers/infiniband/core/ucm.c
+++ b/drivers/infiniband/core/ucm.c
@@ -1202,12 +1202,16 @@ static void ib_ucm_release_dev(struct device *dev)
struct ib_ucm_device *ucm_dev;

ucm_dev = container_of(dev, struct ib_ucm_device, dev);
+ kfree(ucm_dev);
+}
+
+static void ib_ucm_cdev_del(struct ib_ucm_device *ucm_dev)
+{
cdev_del(&ucm_dev->cdev);
if (ucm_dev->devnum < IB_UCM_MAX_DEVICES)
clear_bit(ucm_dev->devnum, dev_map);
else
clear_bit(ucm_dev->devnum - IB_UCM_MAX_DEVICES, overflow_map);
- kfree(ucm_dev);
}

static const struct file_operations ucm_fops = {
@@ -1263,6 +1267,7 @@ static void ib_ucm_add_one(struct ib_device *device)
if (!ucm_dev)
return;

+ device_initialize(&ucm_dev->dev);
ucm_dev->ib_dev = device;

devnum = find_first_zero_bit(dev_map, IB_UCM_MAX_DEVICES);
@@ -1280,18 +1285,19 @@ static void ib_ucm_add_one(struct ib_device *device)
set_bit(devnum, dev_map);
}

+ ucm_dev->dev.devt = base;
+ ucm_dev->dev.release = ib_ucm_release_dev;
+
cdev_init(&ucm_dev->cdev, &ucm_fops);
ucm_dev->cdev.owner = THIS_MODULE;
kobject_set_name(&ucm_dev->cdev.kobj, "ucm%d", ucm_dev->devnum);
- if (cdev_add(&ucm_dev->cdev, base, 1))
+ if (device_add_cdev(&ucm_dev->dev, &ucm_dev->cdev))
goto err;

ucm_dev->dev.class = &cm_class;
ucm_dev->dev.parent = device->dma_device;
- ucm_dev->dev.devt = ucm_dev->cdev.dev;
- ucm_dev->dev.release = ib_ucm_release_dev;
dev_set_name(&ucm_dev->dev, "ucm%d", ucm_dev->devnum);
- if (device_register(&ucm_dev->dev))
+ if (device_add(&ucm_dev->dev))
goto err_cdev;

if (device_create_file(&ucm_dev->dev, &dev_attr_ibdev))
@@ -1303,13 +1309,9 @@ static void ib_ucm_add_one(struct ib_device *device)
err_dev:
device_unregister(&ucm_dev->dev);
err_cdev:
- cdev_del(&ucm_dev->cdev);
- if (ucm_dev->devnum < IB_UCM_MAX_DEVICES)
- clear_bit(devnum, dev_map);
- else
- clear_bit(devnum, overflow_map);
+ ib_ucm_cdev_del(ucm_dev);
err:
- kfree(ucm_dev);
+ put_device(&ucm_dev->dev);
return;
}

@@ -1320,6 +1322,7 @@ static void ib_ucm_remove_one(struct ib_device *device, void *client_data)
if (!ucm_dev)
return;

+ ib_ucm_cdev_del(ucm_dev);
device_unregister(&ucm_dev->dev);
}

--
2.7.4