FAILED: patch "[PATCH] cdx: Fix possible UAF error in driver_override_show()" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-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-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 91d44c1afc61a2fec37a9c7a3485368309391e0b
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2025031035-unmoving-oak-e2a9@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

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

From 91d44c1afc61a2fec37a9c7a3485368309391e0b Mon Sep 17 00:00:00 2001
From: Qiu-ji Chen <[email protected]>
Date: Sat, 18 Jan 2025 15:08:33 +0800
Subject: [PATCH] cdx: Fix possible UAF error in driver_override_show()

Fixed a possible UAF problem in driver_override_show() in drivers/cdx/cdx.c

This function driver_override_show() is part of DEVICE_ATTR_RW, which includes both driver_override_show() and driver_override_store(). These functions can be executed concurrently in sysfs.

The driver_override_store() function uses driver_set_override() to update the driver_override value, and driver_set_override() internally locks the device (device_lock(dev)). If driver_override_show() reads cdx_dev->driver_override without locking, it could potentially access a freed pointer if driver_override_store() frees the string concurrently. This could lead to printing a kernel address, which is a security risk since DEVICE_ATTR can be read by all users.

Additionally, a similar pattern is used in drivers/amba/bus.c, as well as many other bus drivers, where device_lock() is taken in the show function, and it has been working without issues.

This potential bug was detected by our experimental static analysis tool, which analyzes locking APIs and paired functions to identify data races and atomicity violations.

index c573ed2ee71a..7811aa734053 100644
@@ -473,8 +473,12 @@ static ssize_t driver_override_show(struct device *dev,
 				    struct device_attribute *attr, char *buf)
 {
 	struct cdx_device *cdx_dev = to_cdx_device(dev);
+	ssize_t len;
 
-	return sysfs_emit(buf, "%s\n", cdx_dev->driver_override);
+	device_lock(dev);
+	len = sysfs_emit(buf, "%s\n", cdx_dev->driver_override);
+	device_unlock(dev);
+	return len;
 }
 static DEVICE_ATTR_RW(driver_override);