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From: Dmitry Vyukov <dvyukov@google.com>
To: Walter Wu <walter-zh.wu@mediatek.com>
Cc: wsd_upstream <wsd_upstream@mediatek.com>,
	linux-mediatek@lists.infradead.org,
	LKML <linux-kernel@vger.kernel.org>,
	kasan-dev <kasan-dev@googlegroups.com>,
	Linux-MM <linux-mm@kvack.org>,
	Alexander Potapenko <glider@google.com>,
	Matthias Brugger <matthias.bgg@gmail.com>,
	Andrey Ryabinin <aryabinin@virtuozzo.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH] kasan: fix the missing underflow in memmove and memcpy with CONFIG_KASAN_GENERIC=y
Date: Fri, 27 Sep 2019 21:41:51 +0200	[thread overview]
Message-ID: <CACT4Y+YuAxhKtL7ho7jpVAPkjG-JcGyczMXmw8qae2iaZjTh_w@mail.gmail.com> (raw)
In-Reply-To: <1569594142.9045.24.camel@mtksdccf07>

On Fri, Sep 27, 2019 at 4:22 PM Walter Wu <walter-zh.wu@mediatek.com> wrote:
>
> On Fri, 2019-09-27 at 15:07 +0200, Dmitry Vyukov wrote:
> > On Fri, Sep 27, 2019 at 5:43 AM Walter Wu <walter-zh.wu@mediatek.com> wrote:
> > >
> > > memmove() and memcpy() have missing underflow issues.
> > > When -7 <= size < 0, then KASAN will miss to catch the underflow issue.
> > > It looks like shadow start address and shadow end address is the same,
> > > so it does not actually check anything.
> > >
> > > The following test is indeed not caught by KASAN:
> > >
> > >         char *p = kmalloc(64, GFP_KERNEL);
> > >         memset((char *)p, 0, 64);
> > >         memmove((char *)p, (char *)p + 4, -2);
> > >         kfree((char*)p);
> > >
> > > It should be checked here:
> > >
> > > void *memmove(void *dest, const void *src, size_t len)
> > > {
> > >         check_memory_region((unsigned long)src, len, false, _RET_IP_);
> > >         check_memory_region((unsigned long)dest, len, true, _RET_IP_);
> > >
> > >         return __memmove(dest, src, len);
> > > }
> > >
> > > We fix the shadow end address which is calculated, then generic KASAN
> > > get the right shadow end address and detect this underflow issue.
> > >
> > > [1] https://bugzilla.kernel.org/show_bug.cgi?id=199341
> > >
> > > Signed-off-by: Walter Wu <walter-zh.wu@mediatek.com>
> > > Reported-by: Dmitry Vyukov <dvyukov@google.com>
> > > ---
> > >  lib/test_kasan.c   | 36 ++++++++++++++++++++++++++++++++++++
> > >  mm/kasan/generic.c |  8 ++++++--
> > >  2 files changed, 42 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/lib/test_kasan.c b/lib/test_kasan.c
> > > index b63b367a94e8..8bd014852556 100644
> > > --- a/lib/test_kasan.c
> > > +++ b/lib/test_kasan.c
> > > @@ -280,6 +280,40 @@ static noinline void __init kmalloc_oob_in_memset(void)
> > >         kfree(ptr);
> > >  }
> > >
> > > +static noinline void __init kmalloc_oob_in_memmove_underflow(void)
> > > +{
> > > +       char *ptr;
> > > +       size_t size = 64;
> > > +
> > > +       pr_info("underflow out-of-bounds in memmove\n");
> > > +       ptr = kmalloc(size, GFP_KERNEL);
> > > +       if (!ptr) {
> > > +               pr_err("Allocation failed\n");
> > > +               return;
> > > +       }
> > > +
> > > +       memset((char *)ptr, 0, 64);
> > > +       memmove((char *)ptr, (char *)ptr + 4, -2);
> > > +       kfree(ptr);
> > > +}
> > > +
> > > +static noinline void __init kmalloc_oob_in_memmove_overflow(void)
> > > +{
> > > +       char *ptr;
> > > +       size_t size = 64;
> > > +
> > > +       pr_info("overflow out-of-bounds in memmove\n");
> > > +       ptr = kmalloc(size, GFP_KERNEL);
> > > +       if (!ptr) {
> > > +               pr_err("Allocation failed\n");
> > > +               return;
> > > +       }
> > > +
> > > +       memset((char *)ptr, 0, 64);
> > > +       memmove((char *)ptr + size, (char *)ptr, 2);
> > > +       kfree(ptr);
> > > +}
> > > +
> > >  static noinline void __init kmalloc_uaf(void)
> > >  {
> > >         char *ptr;
> > > @@ -734,6 +768,8 @@ static int __init kmalloc_tests_init(void)
> > >         kmalloc_oob_memset_4();
> > >         kmalloc_oob_memset_8();
> > >         kmalloc_oob_memset_16();
> > > +       kmalloc_oob_in_memmove_underflow();
> > > +       kmalloc_oob_in_memmove_overflow();
> > >         kmalloc_uaf();
> > >         kmalloc_uaf_memset();
> > >         kmalloc_uaf2();
> > > diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
> > > index 616f9dd82d12..34ca23d59e67 100644
> > > --- a/mm/kasan/generic.c
> > > +++ b/mm/kasan/generic.c
> > > @@ -131,9 +131,13 @@ static __always_inline bool memory_is_poisoned_n(unsigned long addr,
> > >                                                 size_t size)
> > >  {
> > >         unsigned long ret;
> > > +       void *shadow_start = kasan_mem_to_shadow((void *)addr);
> > > +       void *shadow_end = kasan_mem_to_shadow((void *)addr + size - 1) + 1;
> > >
> > > -       ret = memory_is_nonzero(kasan_mem_to_shadow((void *)addr),
> > > -                       kasan_mem_to_shadow((void *)addr + size - 1) + 1);
> > > +       if ((long)size < 0)
> > > +               shadow_end = kasan_mem_to_shadow((void *)addr + size);
> >
> > Hi Walter,
> >
> > Thanks for working on this.
> >
> > If size<0, does it make sense to continue at all? We will still check
> > 1PB of shadow memory? What happens when we pass such huge range to
> > memory_is_nonzero?
> > Perhaps it's better to produce an error and bail out immediately if size<0?
>
> I agree with what you said. when size<0, it is indeed an unreasonable
> behavior, it should be blocked from continuing to do.
>
>
> > Also, what's the failure mode of the tests? Didn't they badly corrupt
> > memory? We tried to keep tests such that they produce the KASAN
> > reports, but don't badly corrupt memory b/c/ we need to run all of
> > them.
>
> Maybe we should first produce KASAN reports and then go to execute
> memmove() or do nothing? It looks like it’s doing the following.or?
>
> void *memmove(void *dest, const void *src, size_t len)
>  {
> +       if (long(len) <= 0)

/\/\/\/\/\/\

This check needs to be inside of check_memory_region, otherwise we
will have similar problems in all other places that use
check_memory_region.
But check_memory_region already returns a bool, so we could check that
bool and return early.


> +               kasan_report_invalid_size(src, dest, len, _RET_IP_);
> +
>         check_memory_region((unsigned long)src, len, false, _RET_IP_);
>         check_memory_region((unsigned long)dest, len, true, _RET_IP_);
>
>
>

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  reply	other threads:[~2019-09-27 19:42 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-27  3:43 Walter Wu
2019-09-27 13:07 ` Dmitry Vyukov
2019-09-27 14:22   ` Walter Wu
2019-09-27 19:41     ` Dmitry Vyukov [this message]
2019-09-30  4:36       ` Walter Wu
2019-09-30  8:57         ` Marc Gonzalez
2019-10-01  2:36           ` Walter Wu
2019-10-01  3:01             ` Dmitry Vyukov
2019-10-01  3:18               ` Walter Wu
2019-10-02 12:15         ` Walter Wu
2019-10-02 13:57           ` Dmitry Vyukov
2019-10-03  2:17             ` Walter Wu
2019-10-03  6:26               ` Dmitry Vyukov
2019-10-03  9:38                 ` Walter Wu
2019-10-03 13:51                   ` Walter Wu
2019-10-03 14:53                     ` Dmitry Vyukov
2019-10-04  4:42                       ` Walter Wu
2019-10-04  8:02                         ` Walter Wu
2019-10-04  9:18                           ` Dmitry Vyukov
2019-10-04  9:44                             ` Walter Wu
2019-10-04  9:54                               ` Dmitry Vyukov
2019-10-04 12:05                                 ` Walter Wu
2019-10-04 13:52                                   ` Dmitry Vyukov
2019-10-07  3:22                                     ` Walter Wu
2019-10-07  7:29                                       ` Dmitry Vyukov
2019-10-07  8:18                                         ` Walter Wu
2019-10-07  8:24                                           ` Dmitry Vyukov
2019-10-07  8:51                                             ` Walter Wu
2019-10-07  8:54                                               ` Dmitry Vyukov
2019-10-07  9:03                                                 ` Walter Wu
2019-10-07  9:10                                                   ` Dmitry Vyukov
2019-10-07  9:28                                                     ` Walter Wu
2019-10-07  9:50                                                       ` Walter Wu
2019-10-07 10:51                                                         ` Dmitry Vyukov
2019-10-07 12:03                                                           ` Walter Wu
2019-10-07 12:19                                                             ` Dmitry Vyukov
2019-10-07 12:32                                                               ` Walter Wu
2019-10-07 13:33                                                                 ` Dmitry Vyukov
2019-10-08  6:15                                                                   ` Walter Wu
2019-10-08  9:47                                                                     ` Qian Cai
2019-10-08 11:02                                                                       ` Walter Wu
2019-10-08 11:42                                                                         ` Qian Cai
2019-10-08 12:07                                                                           ` Walter Wu
2019-10-08 12:11                                                                           ` Dmitry Vyukov
2019-10-14  2:19                                                                             ` Walter Wu

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