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

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Phil and I found out a problem with commit:

  7e860a6e7a ("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: 7e860a6e7a ("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>
This commit is contained in:
Quentin Casasnovas 2015-04-14 11:25:43 +02:00 committed by Greg Kroah-Hartman
parent bb304b71f8
commit 0d3bba0287
1 changed files with 6 additions and 1 deletions
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7
drivers/usb/class/cdc-acm.c
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@ -1142,11 +1142,16 @@ 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;
}
elength = buffer[0];
switch (buffer[2]) {
case USB_CDC_UNION_TYPE: /* we've found it */