driver core: generalize driver_override in struct device

Currently, there are 12 busses (including platform and PCI) that
duplicate the driver_override logic for their individual devices.

All of them seem to be prone to the bug described in [1].

While this could be solved for every bus individually using a separate
lock, solving this in the driver-core generically results in less (and
cleaner) changes overall.

Thus, move driver_override to struct device, provide corresponding
accessors for busses and handle locking with a separate lock internally.

In particular, add device_set_driver_override(),
device_has_driver_override(), device_match_driver_override() and
generalize the sysfs store() and show() callbacks via a driver_override
feature flag in struct bus_type.

Until all busses have migrated, keep driver_set_override() in place.

Note that we can't use the device lock for the reasons described in [2].

Link: https://bugzilla.kernel.org/show_bug.cgi?id=220789 [1]
Link: https://lore.kernel.org/driver-core/DGRGTIRHA62X.3RY09D9SOK77P@kernel.org/ [2]
Tested-by: Gui-Dong Han <hanguidong02@gmail.com>
Co-developed-by: Gui-Dong Han <hanguidong02@gmail.com>
Signed-off-by: Gui-Dong Han <hanguidong02@gmail.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://patch.msgid.link/20260303115720.48783-2-dakr@kernel.org
[ Use dev->bus instead of sp->bus for consistency; fix commit message to
  refer to the struct bus_type's driver_override feature flag. - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

1 files changed, 60 insertions, 0 deletions

diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index bea8da5f8a3a..37c7e54e0e4c 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -381,6 +381,66 @@ static void __exit deferred_probe_exit(void)
 }
 __exitcall(deferred_probe_exit);
 
+int __device_set_driver_override(struct device *dev, const char *s, size_t len)
+{
+	const char *new, *old;
+	char *cp;
+
+	if (!s)
+		return -EINVAL;
+
+	/*
+	 * The stored value will be used in sysfs show callback (sysfs_emit()),
+	 * which has a length limit of PAGE_SIZE and adds a trailing newline.
+	 * Thus we can store one character less to avoid truncation during sysfs
+	 * show.
+	 */
+	if (len >= (PAGE_SIZE - 1))
+		return -EINVAL;
+
+	/*
+	 * Compute the real length of the string in case userspace sends us a
+	 * bunch of \0 characters like python likes to do.
+	 */
+	len = strlen(s);
+
+	if (!len) {
+		/* Empty string passed - clear override */
+		spin_lock(&dev->driver_override.lock);
+		old = dev->driver_override.name;
+		dev->driver_override.name = NULL;
+		spin_unlock(&dev->driver_override.lock);
+		kfree(old);
+
+		return 0;
+	}
+
+	cp = strnchr(s, len, '\n');
+	if (cp)
+		len = cp - s;
+
+	new = kstrndup(s, len, GFP_KERNEL);
+	if (!new)
+		return -ENOMEM;
+
+	spin_lock(&dev->driver_override.lock);
+	old = dev->driver_override.name;
+	if (cp != s) {
+		dev->driver_override.name = new;
+		spin_unlock(&dev->driver_override.lock);
+	} else {
+		/* "\n" passed - clear override */
+		dev->driver_override.name = NULL;
+		spin_unlock(&dev->driver_override.lock);
+
+		kfree(new);
+	}
+	kfree(old);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(__device_set_driver_override);
+
 /**
  * device_is_bound() - Check if device is bound to a driver
  * @dev: device to check