Commit da797a4c authored Apr 14, 2015 by Quentin Casasnovas Committed by Sasha Levin May 17, 2015

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



[ Upstream commit 0d3bba0287d4e284c3ec7d3397e81eec920d5e7e ]

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.

Fixes: 7e860a6e7aa6 ("cdc-acm: add sanity checks")
Signed-off-by: Phil Turnbull <phil.turnbull@oracle.com>
Signed-off-by: Quentin Casasnovas <quentin.casasnovas@oracle.com>
CC: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
CC: Oliver Neukum <oneukum@suse.de>
CC: Adam Lee <adam8157@gmail.com>
CC: <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>

parent 57f086bc

drivers/usb/class/cdc-acm.c

+6 −0

Original line number	Original line	Diff line number	Diff line
	@@ -1133,6 +1133,12 @@ static int acm_probe(struct usb_interface *intf,
	}		}

	while (buflen > 0) {		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) {		if (buffer[1] != USB_DT_CS_INTERFACE) {
	dev_err(&intf->dev, "skipping garbage\n");		dev_err(&intf->dev, "skipping garbage\n");
	goto next_desc;		goto next_desc;