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>

diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index b6ae24d53db1ee25338c094b40645ff24a6d593b..12d37aedc66f3036785d0cf93de6a8e7cc468696 100644 (file)
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -1133,6 +1133,12 @@ static int acm_probe(struct usb_interface *intf,
        }
 
        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;