usb: chipidea: debug: avoid out of bound read

A string written by the user may not be zero terminated.

sscanf may read memory beyond the buffer if no zero byte
is found.

For testing build with CONFIG_USB_CHIPIDEA=y, CONFIG_USB_CHIPIDEA_DEBUG=y.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Peter Chen <peter.chen@freescale.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/drivers/usb/chipidea/debug.c b/drivers/usb/chipidea/debug.c
index dfb05edcdb96..5b7061a33103 100644
--- a/drivers/usb/chipidea/debug.c
+++ b/drivers/usb/chipidea/debug.c
@@ -88,9 +88,13 @@ static ssize_t ci_port_test_write(struct file *file, const char __user *ubuf,
         char buf[32];
         int ret;
 
-        if (copy_from_user(buf, ubuf, min_t(size_t, sizeof(buf) - 1, count)))
+        count = min_t(size_t, sizeof(buf) - 1, count);
+        if (copy_from_user(buf, ubuf, count))
                 return -EFAULT;
 
+        /* sscanf requires a zero terminated string */
+        buf[count] = '\0';
+
         if (sscanf(buf, "%u", &mode) != 1)
                 return -EINVAL;