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SubjectRe: [PATCH] cdc-acm: prevent infinite loop when parsing CDC headers.
Adding Greg on CC as suggested by Oliver.

On Mon, Apr 13, 2015 at 05:24:04PM +0200, Quentin Casasnovas wrote:
> Phil and I found out a problem with commit:
>
> 7e860a6e ("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: 7e860a6e ("cdc-acm: add sanity checks")
> Signed-off-by: Phil Turnbull <phil.turnbull@oracle.com>
> Signed-off-by: Quentin Casasnovas <quentin.casasnovas@oracle.com>
> CC: Oliver Neukum <oneukum@suse.de>
> CC: Adam Lee <adam8157@gmail.com>
> ---
> drivers/usb/class/cdc-acm.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
> index 6836177..1ac4587 100644
> --- a/drivers/usb/class/cdc-acm.c
> +++ b/drivers/usb/class/cdc-acm.c
> @@ -1133,11 +1133,12 @@ static int acm_probe(struct usb_interface *intf,
> }
>
> while (buflen > 0) {
> + if ((elength = buffer[0]) == 0)
> + break;
> 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 */
> --
> 2.0.5
>


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