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From:   Wolfram Sang <wsa+renesas@sang-engineering.com>
To:     linux-renesas-soc@vger.kernel.org
Cc:     Wolfram Sang <wsa+renesas@sang-engineering.com>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Jason Wang <jasowang@redhat.com>,
        Xuan Zhuo <xuanzhuo@linux.alibaba.com>,
        weiping zhang <zhangweiping@didichuxing.com>,
        Cornelia Huck <cohuck@redhat.com>,
        virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH] virtio-mmio: don't break lifecycle of vm_dev
Date:   Thu, 29 Jun 2023 14:05:26 +0200
Message-Id: <20230629120526.7184-1-wsa+renesas@sang-engineering.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

vm_dev has a separate lifecycle because it has a 'struct device'
embedded. Thus, having a release callback for it is correct.

Allocating the vm_dev struct with devres totally breaks this protection,
though. Instead of waiting for the vm_dev release callback, the memory
is freed when the platform_device is removed. Resulting in a
use-after-free when finally the callback is to be called.

To easily see the problem, compile the kernel with
CONFIG_DEBUG_KOBJECT_RELEASE and unbind with sysfs.

The fix is easy, don't use devres in this case.

Found during my research about object lifetime problems.

Fixes: 7eb781b1bbb7 ("virtio_mmio: add cleanup for virtio_mmio_probe")
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
---
 drivers/virtio/virtio_mmio.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
index a46a4a29e929..97760f611295 100644
--- a/drivers/virtio/virtio_mmio.c
+++ b/drivers/virtio/virtio_mmio.c
@@ -607,9 +607,8 @@ static void virtio_mmio_release_dev(struct device *_d)
 	struct virtio_device *vdev =
 			container_of(_d, struct virtio_device, dev);
 	struct virtio_mmio_device *vm_dev = to_virtio_mmio_device(vdev);
-	struct platform_device *pdev = vm_dev->pdev;
 
-	devm_kfree(&pdev->dev, vm_dev);
+	kfree(vm_dev);
 }
 
 /* Platform device */
@@ -620,7 +619,7 @@ static int virtio_mmio_probe(struct platform_device *pdev)
 	unsigned long magic;
 	int rc;
 
-	vm_dev = devm_kzalloc(&pdev->dev, sizeof(*vm_dev), GFP_KERNEL);
+	vm_dev = kzalloc(sizeof(*vm_dev), GFP_KERNEL);
 	if (!vm_dev)
 		return -ENOMEM;
 
-- 
2.35.1