Date: Mon, 30 Oct 2017 19:47:04 -0700 From: Kees Cook <keescook@...omium.org> To: "Tobin C. Harding" <me@...in.cc> Cc: kernel test robot <xiaolong.ye@...el.com>, kernel-hardening@...ts.openwall.com, "Jason A. Donenfeld" <Jason@...c4.com>, "Theodore Ts'o" <tytso@....edu>, Linus Torvalds <torvalds@...ux-foundation.org>, Paolo Bonzini <pbonzini@...hat.com>, Tycho Andersen <tycho@...ker.com>, "Roberts, William C" <william.c.roberts@...el.com>, Tejun Heo <tj@...nel.org>, Jordan Glover <Golden_Miller83@...tonmail.ch>, Greg KH <gregkh@...uxfoundation.org>, Petr Mladek <pmladek@...e.com>, Joe Perches <joe@...ches.com>, Ian Campbell <ijc@...lion.org.uk>, Sergey Senozhatsky <sergey.senozhatsky@...il.com>, Catalin Marinas <catalin.marinas@....com>, Will Deacon <wilal.deacon@....com>, Steven Rostedt <rostedt@...dmis.org>, Chris Fries <cfries@...gle.com>, Dave Weinstein <olorin@...gle.com>, Daniel Micay <danielmicay@...il.com>, Djalal Harouni <tixxdz@...il.com>, LKML <linux-kernel@...r.kernel.org>, LKP <lkp@...org> Subject: Re: [lkp-robot] [printk] 7f7c60e066: BUG:KASAN:slab-out-of-bounds On Mon, Oct 30, 2017 at 7:39 PM, Tobin C. Harding <me@...in.cc> wrote: > 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@...el.com> wrote: > > thanks for looking at this, I was at a loss as to what (if any) action I > needed to take. I have finally learned after several instances that if 0day produces a report, it's real. :) Even the crazy stuff I haven't been able to reproduce on my own has come back to bite me later, so now I'm very attentive to 0day report. ;) >> > 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. Yeah, looks like it. >> 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. Yeah, looks like it. > I don't know what I should be doing about > > [ 39.757461] BUG: KASAN: slab-out-of-bounds in __test+0xee/0x13f Yeah, I have no idea where this error came from. It does seem triggered by the printf self-test code, though, so if a KASAN bulid doesn't show it, maybe a full SLAB DEBUG build will? -Kees -- Kees Cook Pixel Security
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