Patch "cdc-acm: prevent infinite loop when parsing CDC headers." has been added to the 4.0-stable tree

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

cdc-acm: prevent infinite loop when parsing CDC headers.

to the 4.0-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:
cdc-acm-prevent-infinite-loop-when-parsing-cdc-headers.patch
and it can be found in the queue-4.0 subdirectory.

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

From: Quentin Casasnovas <[email protected]>
Date: Tue, 14 Apr 2015 11:25:43 +0200
Subject: cdc-acm: prevent infinite loop when parsing CDC headers.

From: Quentin Casasnovas <[email protected]>

commit 0d3bba0287d4e284c3ec7d3397e81eec920d5e7e upstream.

Phil and I found out a problem with commit:

7e860a6e7aa6 ("cdc-acm: add sanity checks")

It added some sanity checks to ignore potential garbage in CDC headers but also introduced a potential infinite loop. This can happen at the first loop iteration (elength = 0 in that case) if the description isn't a DT_CS_INTERFACE or later if 'buffer[0]' is zero.

It should also be noted that the wrong length was being added to 'buffer' in case 'buffer[1]' was not a DT_CS_INTERFACE descriptor, since elength was assigned after that check in the loop.

A specially crafted USB device could be used to trigger this infinite loop.

---
 drivers/usb/class/cdc-acm.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

@@ -1133,11 +1133,16 @@ static int acm_probe(struct usb_interfac
 	}
 
 	while (buflen > 0) {
+		elength = buffer[0];
+		if (!elength) {
+			dev_err(&intf->dev, "skipping garbage byte\n");
+			elength = 1;
+			goto next_desc;
+		}
 		if (buffer[1] != USB_DT_CS_INTERFACE) {
 			dev_err(&intf->dev, "skipping garbage\n");
 			goto next_desc;
 		}
-		elength = buffer[0];
 
 		switch (buffer[2]) {
 		case USB_CDC_UNION_TYPE: /* we've found it */

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

queue-4.0/cdc-acm-prevent-infinite-loop-when-parsing-cdc-headers.patch