Patch "thunderbolt: Allow clearing the key" has been added to the 4.13-stable tree

This is a note to let you know that I've just added the patch titled

thunderbolt: Allow clearing the key

to the 4.13-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
thunderbolt-allow-clearing-the-key.patch
and it can be found in the queue-4.13 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: "Bernat, Yehezkel" <[email protected]>
Date: Tue, 15 Aug 2017 08:19:20 +0300
Subject: thunderbolt: Allow clearing the key

From: Bernat, Yehezkel <[email protected]>

commit e545f0d8a54a9594fe604d67d80ca6fddf72ca59 upstream.

If secure authentication of a devices fails, either because the device already has another key uploaded, or there is some other error sending challenge to the device, and the user only wants to approve the device just once (without a new key being uploaded to the device) the current implementation does not allow this because the key cannot be cleared once set even if we allow it to be changed.

Make this scenario possible and allow clearing the key by writing empty string to the key sysfs file.

---
 Documentation/ABI/testing/sysfs-bus-thunderbolt |    2 ++
 drivers/thunderbolt/switch.c                    |   15 +++++++++++----
 2 files changed, 13 insertions(+), 4 deletions(-)

@@ -45,6 +45,8 @@ Contact:	[email protected]
 Description:	When a devices supports Thunderbolt secure connect it will
 		have this attribute. Writing 32 byte hex string changes
 		authorization to use the secure connection method instead.
+		Writing an empty string clears the key and regular connection
+		method can be used again.
 
 What:		/sys/bus/thunderbolt/devices/.../device
 Date:		Sep 2017

@@ -807,8 +807,11 @@ static ssize_t key_store(struct device *
 	struct tb_switch *sw = tb_to_switch(dev);
 	u8 key[TB_SWITCH_KEY_SIZE];
 	ssize_t ret = count;
+	bool clear = false;
 
-	if (hex2bin(key, buf, sizeof(key)))
+	if (!strcmp(buf, "\n"))
+		clear = true;
+	else if (hex2bin(key, buf, sizeof(key)))
 		return -EINVAL;
 
 	if (mutex_lock_interruptible(&switch_lock))

@@ -818,9 +821,13 @@ static ssize_t key_store(struct device *
 		ret = -EBUSY;
 	} else {
 		kfree(sw->key);
-		sw->key = kmemdup(key, sizeof(key), GFP_KERNEL);
-		if (!sw->key)
-			ret = -ENOMEM;
+		if (clear) {
+			sw->key = NULL;
+		} else {
+			sw->key = kmemdup(key, sizeof(key), GFP_KERNEL);
+			if (!sw->key)
+				ret = -ENOMEM;
+		}
 	}
 
 	mutex_unlock(&switch_lock);

Patches currently in stable-queue which might be from [email protected] are

queue-4.13/thunderbolt-make-key-root-only-accessible.patch queue-4.13/thunderbolt-remove-superfluous-check.patch queue-4.13/thunderbolt-allow-clearing-the-key.patch