linux-kernel - [PATCH 1/1] uio: Fix uio

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Date:   Wed,  7 Jun 2017 15:06:44 -0500
From:   Mike Christie <mchristi@...hat.com>
To:     manish.rangankar@...ium.com, target-devel@...r.kernel.org,
        nab@...ux-iscsi.org, kys@...rosoft.com, haiyangz@...rosoft.com,
        sthemmin@...rosoft.com, gregkh@...uxfoundation.org, mst@...hat.com,
        linux-kernel@...r.kernel.org
Cc:     Mike Christie <mchristi@...hat.com>
Subject: [PATCH 1/1] uio: Fix uio_device memory leak

It looks like there might be 2 issues with the uio_device allocation, or it
looks like we are leaking the device for possibly a specific type of device
case that I could not find but one of you may know about.

Issues:
1. We use devm_kzalloc to allocate the uio_device, but the release
function, devm_kmalloc_release, is just a noop, so the memory is never freed.

2. We are actually assigning the resource allocated by devm_kzalloc to
the parent device and not the device that goes with the uio_device.
If devm_kmalloc_release did free the memory, it would not actually be
freed until the parent is which in a lot of cases is not until module
removal, so there could have been thousands of uio_registe/unregister_device
sequences.

It seems like this is either a bug, or was done deliberately to support
some type of device that needs that memory to not be freed. I
checked upstream uio users, but did not see any type of device like this
though.

If this is a bug, this patch, made over Linus's tree, fixes the problems by 
just allocating the uio_device with the uio_info struct since they need to be
allocated/freed/accessed at the same times.

Signed-off-by: Mike Christie <mchristi@...hat.com>
---
 drivers/target/target_core_user.c |  6 +++---
 drivers/uio/uio.c                 | 17 +++++------------
 include/linux/uio_driver.h        |  2 +-
 3 files changed, 9 insertions(+), 16 deletions(-)

diff --git a/drivers/target/target_core_user.c b/drivers/target/target_core_user.c
index beb5f09..00fde52 100644
--- a/drivers/target/target_core_user.c
+++ b/drivers/target/target_core_user.c
@@ -1299,7 +1299,7 @@ static int tcmu_configure_device(struct se_device *dev)
 	kref_get(&udev->kref);
 
 	ret = tcmu_netlink_event(TCMU_CMD_ADDED_DEVICE, udev->uio_info.name,
-				 udev->uio_info.uio_dev->minor);
+				 udev->uio_info.uio_dev.minor);
 	if (ret)
 		goto err_netlink;
 
@@ -1332,7 +1332,7 @@ static int tcmu_check_and_free_pending_cmd(struct tcmu_cmd *cmd)
 
 static bool tcmu_dev_configured(struct tcmu_dev *udev)
 {
-	return udev->uio_info.uio_dev ? true : false;
+	return !!(udev->se_dev.dev_flags & DF_CONFIGURED);
 }
 
 static void tcmu_blocks_release(struct tcmu_dev *udev)
@@ -1381,7 +1381,7 @@ static void tcmu_free_device(struct se_device *dev)
 
 	if (tcmu_dev_configured(udev)) {
 		tcmu_netlink_event(TCMU_CMD_REMOVED_DEVICE, udev->uio_info.name,
-				   udev->uio_info.uio_dev->minor);
+				   udev->uio_info.uio_dev.minor);
 
 		uio_unregister_device(&udev->uio_info);
 	}
diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
index ff04b7f..7593db6 100644
--- a/drivers/uio/uio.c
+++ b/drivers/uio/uio.c
@@ -399,7 +399,7 @@ static void uio_free_minor(struct uio_device *idev)
  */
 void uio_event_notify(struct uio_info *info)
 {
-	struct uio_device *idev = info->uio_dev;
+	struct uio_device *idev = &info->uio_dev;
 
 	atomic_inc(&idev->event);
 	wake_up_interruptible(&idev->wait);
@@ -812,13 +812,8 @@ int __uio_register_device(struct module *owner,
 	if (!parent || !info || !info->name || !info->version)
 		return -EINVAL;
 
-	info->uio_dev = NULL;
-
-	idev = devm_kzalloc(parent, sizeof(*idev), GFP_KERNEL);
-	if (!idev) {
-		return -ENOMEM;
-	}
-
+	idev = &info->uio_dev;
+	memset(idev, 0, sizeof(*idev));
 	idev->owner = owner;
 	idev->info = info;
 	init_waitqueue_head(&idev->wait);
@@ -841,8 +836,6 @@ int __uio_register_device(struct module *owner,
 	if (ret)
 		goto err_uio_dev_add_attributes;
 
-	info->uio_dev = idev;
-
 	if (info->irq && (info->irq != UIO_IRQ_CUSTOM)) {
 		/*
 		 * Note that we deliberately don't use devm_request_irq
@@ -879,10 +872,10 @@ void uio_unregister_device(struct uio_info *info)
 {
 	struct uio_device *idev;
 
-	if (!info || !info->uio_dev)
+	if (!info)
 		return;
 
-	idev = info->uio_dev;
+	idev = &info->uio_dev;
 
 	uio_free_minor(idev);
 
diff --git a/include/linux/uio_driver.h b/include/linux/uio_driver.h
index 3c85c81..4b1b1c8 100644
--- a/include/linux/uio_driver.h
+++ b/include/linux/uio_driver.h
@@ -95,7 +95,7 @@ struct uio_device {
  * @irqcontrol:		disable/enable irqs when 0/1 is written to /dev/uioX
  */
 struct uio_info {
-	struct uio_device	*uio_dev;
+	struct uio_device	uio_dev;
 	const char		*name;
 	const char		*version;
 	struct uio_mem		mem[MAX_UIO_MAPS];
-- 
2.7.2