From: Dmitry Vyukov <dvyukov@google.com>
To: Walter Wu <walter-zh.wu@mediatek.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>,
Alexander Potapenko <glider@google.com>,
Matthias Brugger <matthias.bgg@gmail.com>,
LKML <linux-kernel@vger.kernel.org>,
kasan-dev <kasan-dev@googlegroups.com>,
Linux-MM <linux-mm@kvack.org>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
linux-mediatek@lists.infradead.org,
wsd_upstream <wsd_upstream@mediatek.com>
Subject: Re: [PATCH] kasan: fix the missing underflow in memmove and memcpy with CONFIG_KASAN_GENERIC=y
Date: Fri, 27 Sep 2019 15:07:25 +0200 [thread overview]
Message-ID: <CACT4Y+Zxz+R=qQxSMoipXoLjRqyApD3O0eYpK0nyrfGHE4NNPw@mail.gmail.com> (raw)
In-Reply-To: <20190927034338.15813-1-walter-zh.wu@mediatek.com>
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?
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.
> + ret = memory_is_nonzero(shadow_start, shadow_end);
>
> if (unlikely(ret)) {
> unsigned long last_byte = addr + size - 1;
> --
> 2.18.0
>
> --
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> To unsubscribe from this group and stop receiving emails from it, send an email to kasan-dev+unsubscribe@googlegroups.com.
> To view this discussion on the web visit https://groups.google.com/d/msgid/kasan-dev/20190927034338.15813-1-walter-zh.wu%40mediatek.com.
next prev parent reply other threads:[~2019-09-27 13:07 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-27 3:43 [PATCH] kasan: fix the missing underflow in memmove and memcpy with CONFIG_KASAN_GENERIC=y Walter Wu
2019-09-27 13:07 ` Dmitry Vyukov [this message]
2019-09-27 14:22 ` Walter Wu
2019-09-27 19:41 ` Dmitry Vyukov
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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