[PATCH] usb: gadget: printer: fix races against disable

[Oliver Neukum <oneukum@suse.com>]

printer_read() and printer_write() guard against the race
against disable() by checking the dev->interface flag,
which in turn is guarded by a spinlock.
These functions, however, drop the lock on multiple occasions.
This means that the test has to be redone after reacquiring
the lock and before doing IO.

Add the tests.

This also addresses CVE-2024-25741

Fixes: 7f2ca14d2f9b9 ("usb: gadget: function: printer: Interface is disabled and returns error")
Signed-off-by: Oliver Neukum <oneukum@suse.com>
---
 drivers/usb/gadget/function/f_printer.c | 39 ++++++++++++++++++-------
 1 file changed, 29 insertions(+), 10 deletions(-)

diff --git a/drivers/usb/gadget/function/f_printer.c b/drivers/usb/gadget/function/f_printer.c
index 4c0b7c2970f1..44e20c6c36d3 100644
--- a/drivers/usb/gadget/function/f_printer.c
+++ b/drivers/usb/gadget/function/f_printer.c
@@ -450,11 +450,8 @@ printer_read(struct file *fd, char __user *buf, size_t len, loff_t *ptr)
 	mutex_lock(&dev->lock_printer_io);
 	spin_lock_irqsave(&dev->lock, flags);
 
-	if (dev->interface < 0) {
-		spin_unlock_irqrestore(&dev->lock, flags);
-		mutex_unlock(&dev->lock_printer_io);
-		return -ENODEV;
-	}
+	if (dev->interface < 0)
+		goto out_disabled;
 
 	/* We will use this flag later to check if a printer reset happened
 	 * after we turn interrupts back on.
@@ -462,6 +459,9 @@ printer_read(struct file *fd, char __user *buf, size_t len, loff_t *ptr)
 	dev->reset_printer = 0;
 
 	setup_rx_reqs(dev);
+	/* this dropped the lock - need to retest */
+	if (dev->interface < 0)
+		goto out_disabled;
 
 	bytes_copied = 0;
 	current_rx_req = dev->current_rx_req;
@@ -495,6 +495,8 @@ printer_read(struct file *fd, char __user *buf, size_t len, loff_t *ptr)
 		wait_event_interruptible(dev->rx_wait,
 				(likely(!list_empty(&dev->rx_buffers))));
 		spin_lock_irqsave(&dev->lock, flags);
+		if (dev->interface < 0)
+			goto out_disabled;
 	}
 
 	/* We have data to return then copy it to the caller's buffer.*/
@@ -538,6 +540,9 @@ printer_read(struct file *fd, char __user *buf, size_t len, loff_t *ptr)
 			return -EAGAIN;
 		}
 
+		if (dev->interface < 0)
+			goto out_disabled;
+
 		/* If we not returning all the data left in this RX request
 		 * buffer then adjust the amount of data left in the buffer.
 		 * Othewise if we are done with this RX request buffer then
@@ -567,6 +572,11 @@ printer_read(struct file *fd, char __user *buf, size_t len, loff_t *ptr)
 		return bytes_copied;
 	else
 		return -EAGAIN;
+
+out_disabled:
+	spin_unlock_irqrestore(&dev->lock, flags);
+	mutex_unlock(&dev->lock_printer_io);
+	return -ENODEV;
 }
 
 static ssize_t
@@ -587,11 +597,8 @@ printer_write(struct file *fd, const char __user *buf, size_t len, loff_t *ptr)
 	mutex_lock(&dev->lock_printer_io);
 	spin_lock_irqsave(&dev->lock, flags);
 
-	if (dev->interface < 0) {
-		spin_unlock_irqrestore(&dev->lock, flags);
-		mutex_unlock(&dev->lock_printer_io);
-		return -ENODEV;
-	}
+	if (dev->interface < 0)
+		goto out_disabled;
 
 	/* Check if a printer reset happens while we have interrupts on */
 	dev->reset_printer = 0;
@@ -614,6 +621,8 @@ printer_write(struct file *fd, const char __user *buf, size_t len, loff_t *ptr)
 		wait_event_interruptible(dev->tx_wait,
 				(likely(!list_empty(&dev->tx_reqs))));
 		spin_lock_irqsave(&dev->lock, flags);
+		if (dev->interface < 0)
+			goto out_disabled;
 	}
 
 	while (likely(!list_empty(&dev->tx_reqs)) && len) {
@@ -663,6 +672,9 @@ printer_write(struct file *fd, const char __user *buf, size_t len, loff_t *ptr)
 			return -EAGAIN;
 		}
 
+		if (dev->interface < 0)
+			goto out_disabled;
+
 		list_add(&req->list, &dev->tx_reqs_active);
 
 		/* here, we unlock, and only unlock, to avoid deadlock. */
@@ -675,6 +687,8 @@ printer_write(struct file *fd, const char __user *buf, size_t len, loff_t *ptr)
 			mutex_unlock(&dev->lock_printer_io);
 			return -EAGAIN;
 		}
+		if (dev->interface < 0)
+			goto out_disabled;
 	}
 
 	spin_unlock_irqrestore(&dev->lock, flags);
@@ -686,6 +700,11 @@ printer_write(struct file *fd, const char __user *buf, size_t len, loff_t *ptr)
 		return bytes_copied;
 	else
 		return -EAGAIN;
+
+out_disabled:
+	spin_unlock_irqrestore(&dev->lock, flags);
+	mutex_unlock(&dev->lock_printer_io);
+	return -ENODEV;
 }
 
 static int
-- 
2.45.1