FAILED: patch "[PATCH] bus: fsl-mc: fix use-after-free in driver_override_show()" failed to apply to 6.6-stable tree

The patch below does not apply to the 6.6-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-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 148891e95014b5dc5878acefa57f1940c281c431
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026021346-runner-symphony-9463@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

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

From 148891e95014b5dc5878acefa57f1940c281c431 Mon Sep 17 00:00:00 2001
From: Gui-Dong Han <[email protected]>
Date: Wed, 3 Dec 2025 01:44:38 +0800
Subject: [PATCH] bus: fsl-mc: fix use-after-free in driver_override_show()

The driver_override_show() function reads the driver_override string without holding the device_lock. However, driver_override_store() uses driver_set_override(), which modifies and frees the string while holding the device_lock.

This can result in a concurrent use-after-free if the string is freed by the store function while being read by the show function.

Fix this by holding the device_lock around the read operation.

index c08c04047ae2..08b99b0b342f 100644
@@ -231,8 +231,12 @@ static ssize_t driver_override_show(struct device *dev,
 				    struct device_attribute *attr, char *buf)
 {
 	struct fsl_mc_device *mc_dev = to_fsl_mc_device(dev);
+	ssize_t len;
 
-	return sysfs_emit(buf, "%s\n", mc_dev->driver_override);
+	device_lock(dev);
+	len = sysfs_emit(buf, "%s\n", mc_dev->driver_override);
+	device_unlock(dev);
+	return len;
 }
 static DEVICE_ATTR_RW(driver_override);
 

From: Chelsy Ratnawat <[email protected]>

[ Upstream commit a50522c805a6c575c80f41b04706e084d814e116 ]

Use sysfs_emit() instead of snprintf()/sprintf() when writing to sysfs buffers, as recommended by the kernel documentation.

Stable-dep-of: 148891e95014 ("bus: fsl-mc: fix use-after-free in driver_override_show()")

---
 drivers/bus/fsl-mc/fsl-mc-bus.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

index 03642df2df0bb..3db939c619013 100644
@@ -175,8 +175,8 @@ static ssize_t modalias_show(struct device *dev, struct device_attribute *attr,
 {
 	struct fsl_mc_device *mc_dev = to_fsl_mc_device(dev);
 
-	return sprintf(buf, "fsl-mc:v%08Xd%s\n", mc_dev->obj_desc.vendor,
-		       mc_dev->obj_desc.type);
+	return sysfs_emit(buf, "fsl-mc:v%08Xd%s\n", mc_dev->obj_desc.vendor,
+			mc_dev->obj_desc.type);
 }
 static DEVICE_ATTR_RO(modalias);
 

@@ -202,7 +202,7 @@ static ssize_t driver_override_show(struct device *dev,
 {
 	struct fsl_mc_device *mc_dev = to_fsl_mc_device(dev);
 
-	return snprintf(buf, PAGE_SIZE, "%s\n", mc_dev->driver_override);
+	return sysfs_emit(buf, "%s\n", mc_dev->driver_override);
 }
 static DEVICE_ATTR_RW(driver_override);
 

2.51.0

From: Gui-Dong Han <[email protected]>

[ Upstream commit 148891e95014b5dc5878acefa57f1940c281c431 ]

The driver_override_show() function reads the driver_override string without holding the device_lock. However, driver_override_store() uses driver_set_override(), which modifies and frees the string while holding the device_lock.

This can result in a concurrent use-after-free if the string is freed by the store function while being read by the show function.

Fix this by holding the device_lock around the read operation.

---
 drivers/bus/fsl-mc/fsl-mc-bus.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

index 3db939c619013..8b421ef0580a7 100644
@@ -201,8 +201,12 @@ static ssize_t driver_override_show(struct device *dev,
 				    struct device_attribute *attr, char *buf)
 {
 	struct fsl_mc_device *mc_dev = to_fsl_mc_device(dev);
+	ssize_t len;
 
-	return sysfs_emit(buf, "%s\n", mc_dev->driver_override);
+	device_lock(dev);
+	len = sysfs_emit(buf, "%s\n", mc_dev->driver_override);
+	device_unlock(dev);
+	return len;
 }
 static DEVICE_ATTR_RW(driver_override);
 

2.51.0