[kernel-hardening] Re: [lkp-robot] [printk] 7f7c60e066: BUG:KASAN:slab-out-of-bounds

["Tobin C. Harding" <me@tobin.cc>]

On Mon, Oct 30, 2017 at 05:14:59PM -0700, Kees Cook wrote:
> On Wed, Oct 25, 2017 at 9:22 AM, kernel test robot
> <xiaolong.ye@intel.com> wrote:

thanks for looking at this, I was at a loss as to what (if any) action I
needed to take.

> > FYI, we noticed the following commit (built with gcc-4.9):
> >
> > commit: 7f7c60e0663645e757e520245606fde9c6e326bb ("printk: hash addresses printed with %p")
> > url: https://github.com/0day-ci/linux/commits/Tobin-C-Harding/printk-hash-addresses-printed-with-p/20171024-231922
> 
> It's not clear to me which of the various versions this test ran
> against, but it seems like the printf self-tests got very confused by
> the results:
> 
> > [   40.275423] test_printf: kvasprintf(..., "%p %p", ...) returned '3cf9adbe eff717bf', expected '0000000001234567 fffffffffedcba98'
> > [   40.296739] test_printf: vsnprintf(buf, 256, "|%-*p|%*p|", ...) returned 19, expected 39
> > [   40.322776] test_printf: vsnprintf(buf, 16, "|%-*p|%*p|", ...) returned 19, expected 39
> > [   40.334834] test_printf: vsnprintf(buf, 0, "|%-*p|%*p|", ...) returned 19, expected 39
> 
> I assume v10 will fix the width issues, but probably not the value tests...

Oh, so I need to update lib/test_printf.c to cover hashed %p.

> And it claims a use-after-free, too:
> 
> > [   39.757461] The buggy address belongs to the object at 22cb34bb
> > [   39.757461]  which belongs to the cache kmalloc-32 of size 32
> > [   39.757461] The buggy address is located 0 bytes inside of
> > [   39.757461]  32-byte region [22cb34bb, 24ac3a60)
> 
> Which becomes rather unreadable, since the address got hashed. :P

So I think we need to patch mm/kasan/report to use %pK instead of %p.

I don't know what I should be doing about

[   39.757461] BUG: KASAN: slab-out-of-bounds in __test+0xee/0x13f

Awesome, thanks,
Tobin.