On Wed, Aug 07, 2019 at 12:28:06PM -0700, syzbot wrote:
> usercopy: Kernel memory exposure attempt detected from wrapped address
> (offset 0, size 0)!
> ------------[ cut here ]------------
> kernel BUG at mm/usercopy.c:98!
This report is confusing because the arguments to usercopy_abort() are wrong.
/* Reject if object wraps past end of memory. */
if (ptr + n < ptr)
usercopy_abort("wrapped address", NULL, to_user, 0, ptr + n);
ptr + n is not 'size', it's what wrapped. I don't know what 'offset'
should be set to, but 'size' should be 'n'. Presumably we don't want to
report 'ptr' because it'll leak a kernel address ... reporting 'n' will
leak a range for a kernel address, but I think that's OK? Admittedly an
attacker can pass in various values for 'n', but it'll be quite noisy
and leave a trace in the kernel logs for forensics to find afterwards.
> Call Trace:
> check_bogus_address mm/usercopy.c:151 [inline]
> __check_object_size mm/usercopy.c:260 [inline]
> __check_object_size.cold+0xb2/0xba mm/usercopy.c:250
> check_object_size include/linux/thread_info.h:119 [inline]
> check_copy_size include/linux/thread_info.h:150 [inline]
> copy_to_user include/linux/uaccess.h:151 [inline]
> hidraw_ioctl+0x38c/0xae0 drivers/hid/hidraw.c:392
The root problem would appear to be:
else if (copy_to_user(user_arg + offsetof(
struct hidraw_report_descriptor,
value[0]),
dev->hid->rdesc,
min(dev->hid->rsize, len)))
That 'min' should surely be a 'max'?
Jiri, this looks like it was your code back in 2007.
