Patch "xhci: Don't add a virt_dev to the devs array before it's fully allocated" has been added to the 4.14-stable tree

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

xhci: Don't add a virt_dev to the devs array before it's fully allocated

to the 4.14-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:
xhci-don-t-add-a-virt_dev-to-the-devs-array-before-it-s-fully-allocated.patch
and it can be found in the queue-4.14 subdirectory.

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

From: Mathias Nyman <[email protected]>
Date: Fri, 8 Dec 2017 18:10:05 +0200
Subject: xhci: Don't add a virt_dev to the devs array before it's fully allocated

From: Mathias Nyman <[email protected]>

commit 5d9b70f7d52eb14bb37861c663bae44de9521c35 upstream.

Avoid null pointer dereference if some function is walking through the devs array accessing members of a new virt_dev that is mid allocation.

Add the virt_dev to xhci->devs[i] _after_ the virt_device and all its members are properly allocated.

issue found by KASAN: null-ptr-deref in xhci_find_slot_id_by_port

"Quick analysis suggests that xhci_alloc_virt_device() is not mutex protected. If so, there is a time frame where xhci->devs[slot_id] is set but not fully initialized. Specifically, xhci->devs[i]->udev can be NULL."

---
 drivers/usb/host/xhci-mem.c |   15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

@@ -983,10 +983,9 @@ int xhci_alloc_virt_device(struct xhci_h
 		return 0;
 	}
 
-	xhci->devs[slot_id] = kzalloc(sizeof(*xhci->devs[slot_id]), flags);
-	if (!xhci->devs[slot_id])
+	dev = kzalloc(sizeof(*dev), flags);
+	if (!dev)
 		return 0;
-	dev = xhci->devs[slot_id];
 
 	/* Allocate the (output) device context that will be used in the HC. */
 	dev->out_ctx = xhci_alloc_container_ctx(xhci, XHCI_CTX_TYPE_DEVICE, flags);

@@ -1027,9 +1026,17 @@ int xhci_alloc_virt_device(struct xhci_h
 
 	trace_xhci_alloc_virt_device(dev);
 
+	xhci->devs[slot_id] = dev;
+
 	return 1;
 fail:
-	xhci_free_virt_device(xhci, slot_id);
+
+	if (dev->in_ctx)
+		xhci_free_container_ctx(xhci, dev->in_ctx);
+	if (dev->out_ctx)
+		xhci_free_container_ctx(xhci, dev->out_ctx);
+	kfree(dev);
+
 	return 0;
 }
 

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

queue-4.14/usb-xhci-fix-tds-for-mtk-xhci1.1.patch queue-4.14/xhci-don-t-add-a-virt_dev-to-the-devs-array-before-it-s-fully-allocated.patch