Patchwork USB: core: Fix unterminated string returned by usb_string()

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Submitter Alan Stern
Date April 15, 2019, 3:51 p.m.
Message ID <>
Download mbox | patch
Permalink /patch/773333/
State New
Headers show


Alan Stern - April 15, 2019, 3:51 p.m.
Some drivers (such as the vub300 MMC driver) expect usb_string() to
return a properly NUL-terminated string, even when an error occurs.
(In fact, vub300's probe routine doesn't bother to check the return
code from usb_string().)  When the driver goes on to use an
unterminated string, it leads to kernel errors such as
stack-out-of-bounds, as found by the syzkaller USB fuzzer.

An out-of-range string index argument is not at all unlikely, given
that some devices don't provide string descriptors and therefore list
0 as the value for their string indexes.  This patch makes
usb_string() return a properly terminated empty string along with the
-EINVAL error code when an out-of-range index is encountered.

And since a USB string index is a single-byte value, indexes >= 256
are just as invalid as values of 0 or below.

Signed-off-by: Alan Stern <>
CC: <>



 drivers/usb/core/message.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)


Index: usb-devel/drivers/usb/core/message.c
--- usb-devel.orig/drivers/usb/core/message.c
+++ usb-devel/drivers/usb/core/message.c
@@ -820,9 +820,11 @@  int usb_string(struct usb_device *dev, i
 	if (dev->state == USB_STATE_SUSPENDED)
 		return -EHOSTUNREACH;
-	if (size <= 0 || !buf || !index)
+	if (size <= 0 || !buf)
 		return -EINVAL;
 	buf[0] = 0;
+	if (index <= 0 || index >= 256)
+		return -EINVAL;
 	tbuf = kmalloc(256, GFP_NOIO);
 	if (!tbuf)
 		return -ENOMEM;