From: Quentin Casasnovas Date: Tue, 14 Apr 2015 09:25:43 +0000 (+0200) Subject: cdc-acm: prevent infinite loop when parsing CDC headers. X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=0d3bba0287d4e284c3ec7d3397e81eec920d5e7e;p=GitHub%2FLineageOS%2FG12%2Fandroid_kernel_amlogic_linux-4.9.git cdc-acm: prevent infinite loop when parsing CDC headers. 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 Signed-off-by: Quentin Casasnovas CC: Sergei Shtylyov CC: Oliver Neukum CC: Adam Lee CC: Signed-off-by: Greg Kroah-Hartman --- diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c index 3e15add665e2..5c8f58114677 100644 --- a/drivers/usb/class/cdc-acm.c +++ b/drivers/usb/class/cdc-acm.c @@ -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 */