FAILED: patch "[PATCH] USB: misc: yurex: fix race between read and write" failed to apply to 4.19-stable tree

The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-4.19.y
git checkout FETCH_HEAD
git cherry-pick -x 93907620b308609c72ba4b95b09a6aa2658bb553
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2024100159-vista-remold-8a09@gregkh' --subject-prefix 'PATCH 4.19.y' HEAD^..

Possible dependencies:

93907620b308 ("USB: misc: yurex: fix race between read and write") 86b20af11e84 ("usb: yurex: Replace snprintf() with the safer scnprintf() variant")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 93907620b308609c72ba4b95b09a6aa2658bb553 Mon Sep 17 00:00:00 2001
From: Oliver Neukum <[email protected]>
Date: Thu, 12 Sep 2024 15:21:22 +0200
Subject: [PATCH] USB: misc: yurex: fix race between read and write

The write code path touches the bbu member in a non atomic manner without taking the spinlock. Fix it.

The bug is as old as the driver.

index 4745a320eae4..4a9859e03f6b 100644
@@ -404,7 +404,6 @@ static ssize_t yurex_read(struct file *file, char __user *buffer, size_t count,
 	struct usb_yurex *dev;
 	int len = 0;
 	char in_buffer[MAX_S64_STRLEN];
-	unsigned long flags;
 
 	dev = file->private_data;
 

@@ -419,9 +418,9 @@ static ssize_t yurex_read(struct file *file, char __user *buffer, size_t count,
 		return -EIO;
 	}
 
-	spin_lock_irqsave(&dev->lock, flags);
+	spin_lock_irq(&dev->lock);
 	scnprintf(in_buffer, MAX_S64_STRLEN, "%lld\n", dev->bbu);
-	spin_unlock_irqrestore(&dev->lock, flags);
+	spin_unlock_irq(&dev->lock);
 	mutex_unlock(&dev->io_mutex);
 
 	return simple_read_from_buffer(buffer, count, ppos, in_buffer, len);

@@ -511,8 +510,11 @@ static ssize_t yurex_write(struct file *file, const char __user *user_buffer,
 			__func__, retval);
 		goto error;
 	}
-	if (set && timeout)
+	if (set && timeout) {
+		spin_lock_irq(&dev->lock);
 		dev->bbu = c2;
+		spin_unlock_irq(&dev->lock);
+	}
 	return timeout ? count : -EIO;
 
 error: