From: Daniel Axtens <dja@axtens.net>
To: Dmitry Vyukov <dvyukov@google.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>,
Andrew Morton <akpm@linux-foundation.org>,
kasan-dev <kasan-dev@googlegroups.com>,
Christophe Leroy <christophe.leroy@c-s.fr>,
Andrey Ryabinin <aryabinin@virtuozzo.com>,
Alexander Potapenko <glider@google.com>
Subject: Re: [PATCH v3 3/3] kasan: initialise array in kasan_memcmp test
Date: Sat, 25 Apr 2020 00:37:04 +1000 [thread overview]
Message-ID: <877dy5t0fj.fsf@dja-thinkpad.axtens.net> (raw)
In-Reply-To: <CACT4Y+b7omyQ0bBBApOs5O_m0MDZWjoBi3QV6MxG4h_14gUa2g@mail.gmail.com>
Dmitry Vyukov <dvyukov@google.com> writes:
> On Thu, Apr 23, 2020 at 5:45 PM Daniel Axtens <dja@axtens.net> wrote:
>>
>> memcmp may bail out before accessing all the memory if the buffers
>> contain differing bytes. kasan_memcmp calls memcmp with a stack array.
>> Stack variables are not necessarily initialised (in the absence of a
>> compiler plugin, at least). Sometimes this causes the memcpy to bail
>> early thus fail to trigger kasan.
>>
>> Make sure the array initialised to zero in the code.
>>
>> No other test is dependent on the contents of an array on the stack.
>>
>> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
>> Cc: Alexander Potapenko <glider@google.com>
>> Cc: Dmitry Vyukov <dvyukov@google.com>
>> Signed-off-by: Daniel Axtens <dja@axtens.net>
>> Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
>> ---
>> lib/test_kasan.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/lib/test_kasan.c b/lib/test_kasan.c
>> index 939f395a5392..7700097842c8 100644
>> --- a/lib/test_kasan.c
>> +++ b/lib/test_kasan.c
>> @@ -638,7 +638,7 @@ static noinline void __init kasan_memcmp(void)
>> {
>> char *ptr;
>> size_t size = 24;
>> - int arr[9];
>> + int arr[9] = {};
>>
>> pr_info("out-of-bounds in memcmp\n");
>> ptr = kmalloc(size, GFP_KERNEL | __GFP_ZERO);
>
> My version of this function contains the following below:
>
> memset(arr, 0, sizeof(arr));
>
> What am I missing?
Ah! It turns out I accidentally removed the memset in patch 1. No idea
why I did that. I'll fix up patch 1 to not remove the memset and drop
this patch.
Daniel
next prev parent reply other threads:[~2020-04-24 14:37 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-23 15:45 [PATCH v3 0/3] Fix some incompatibilites between KASAN and FORTIFY_SOURCE Daniel Axtens
2020-04-23 15:45 ` [PATCH v3 1/3] kasan: stop tests being eliminated as dead code with FORTIFY_SOURCE Daniel Axtens
2020-04-23 15:45 ` [PATCH v3 2/3] string.h: fix incompatibility between FORTIFY_SOURCE and KASAN Daniel Axtens
2020-04-23 15:45 ` [PATCH v3 3/3] kasan: initialise array in kasan_memcmp test Daniel Axtens
2020-04-23 17:25 ` Dmitry Vyukov
2020-04-24 14:37 ` Daniel Axtens [this message]
2020-04-24 6:54 ` [PATCH v3 0/3] Fix some incompatibilites between KASAN and FORTIFY_SOURCE David Gow
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