[PATCH] uio/uio_pci_generic: Disable bus-mastering on release

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Userspace code using uio_pci_generic may enable bus-mastering by
directly manipulating a PCI device's command register. If a userspace
program enables bus-mastering but exits/crashes uncleanly, bus-
mastering will still be enabled and stale DMA addresses may be
programmed and live in the device.

Disable bus-mastering unconditionally on last close of a UIO PCI fd
to avoid this. If the device did not have bus-mastering enabled,
pci_clear_master() is a no-op.

Signed-off-by: Venkatesh Srinivas <venkateshs@xxxxxxxxxx>
Reviewed-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
Reviewed-by: Catherine Sullivan <csully@xxxxxxxxxx>
---
 drivers/uio/uio_pci_generic.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/uio/uio_pci_generic.c b/drivers/uio/uio_pci_generic.c
index 8773e373ffe5..832af15678ef 100644
--- a/drivers/uio/uio_pci_generic.c
+++ b/drivers/uio/uio_pci_generic.c
@@ -39,6 +39,14 @@ to_uio_pci_generic_dev(struct uio_info *info)
 	return container_of(info, struct uio_pci_generic_dev, info);
 }
 
+static int release(struct uio_info *info, struct inode *inode)
+{
+	struct uio_pci_generic_dev *gdev = to_uio_pci_generic_dev(info);
+	/* Stop the device from initiating further DMAs */
+	pci_clear_master(gdev->pdev);
+	return 0;
+}
+
 /* Interrupt handler. Read/modify/write the command register to disable
  * the interrupt. */
 static irqreturn_t irqhandler(int irq, struct uio_info *info)
@@ -78,6 +86,7 @@ static int probe(struct pci_dev *pdev,
 
 	gdev->info.name = "uio_pci_generic";
 	gdev->info.version = DRIVER_VERSION;
+	gdev->info.release = release;
 	gdev->pdev = pdev;
 	if (pdev->irq) {
 		gdev->info.irq = pdev->irq;
-- 
2.19.1.930.g4563a0d9d0-goog




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