On Thu, Aug 08, 2019 at 02:46:54PM +0200, Greg KH wrote:
> On Thu, Aug 08, 2019 at 05:38:06AM -0700, syzbot wrote:
> > Hello,
> >
> > syzbot found the following crash on:
> >
> > HEAD commit: e96407b4 usb-fuzzer: main usb gadget fuzzer driver
> > git tree: https://github.com/google/kasan.git usb-fuzzer
> > console output: https://syzkaller.appspot.com/x/log.txt?x=13aeaece600000
> > kernel config: https://syzkaller.appspot.com/x/.config?x=cfa2c18fb6a8068e
> > dashboard link: https://syzkaller.appspot.com/bug?extid=45b2f40f0778cfa7634e
> > compiler: gcc (GCC) 9.0.0 20181231 (experimental)
> >
> > Unfortunately, I don't have any reproducer for this crash yet.
> >
> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > Reported-by: syzbot+45b2f40f0778cfa76...@syzkaller.appspotmail.com
> >
> > ldusb 6-1:0.124: Read buffer overflow, -131383996186150 bytes dropped
>
> That's a funny number :)
>
> Nice overflow found, I see you are now starting to fuzz the char device
> nodes of usb drivers...
>
> Michael, care to fix this up?
This looks like the length in the read-from-device buffer is unchecked:
/* actual_buffer contains actual_length + interrupt_in_buffer */
actual_buffer = (size_t *)(dev->ring_buffer + dev->ring_tail *
(sizeof(size_t)+dev->interrupt_in_endpoint_size));
bytes_to_read = min(count, *actual_buffer);
if (bytes_to_read < *actual_buffer)
dev_warn(&dev->intf->dev, "Read buffer overflow, %zd bytes
dropped\n",
*actual_buffer-bytes_to_read);
/* copy one interrupt_in_buffer from ring_buffer into userspace */
if (copy_to_user(buffer, actual_buffer+1, bytes_to_read)) {
retval = -EFAULT;
goto unlock_exit;
}
I assume what's stored at actual_buffer is bogus and needs validation
somewhere before it's actually used. (If not here, maybe where ever the
write into the buffer originally happens?)
--
Kees Cook
