| From | lizf@kernel ... | Subject | [PATCH 3.4 168/172] cdc-acm: prevent infinite loop when parsing CDC headers. | Date | Tue, 16 Jun 2015 16:37:02 +0800 |
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From: Quentin Casasnovas <quentin.casasnovas@oracle.com>
3.4.108-rc1 review patch. If anyone has any objections, please let me know.
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commit 0d3bba0287d4e284c3ec7d3397e81eec920d5e7e upstream.
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> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Zefan Li <lizefan@huawei.com> --- drivers/usb/class/cdc-acm.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c index 57877a9..25bc1d6 100644 --- a/drivers/usb/class/cdc-acm.c +++ b/drivers/usb/class/cdc-acm.c @@ -1044,11 +1044,16 @@ 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 */ -- 1.9.1
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