linux-kernel - Re: [PATCH v4 1/2] kasan: detect negative size in memory operation function

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Date:   Thu, 21 Nov 2019 21:09:13 +0800
From:   Walter Wu <walter-zh.wu@...iatek.com>
To:     Andrey Ryabinin <aryabinin@...tuozzo.com>
CC:     Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        <kasan-dev@...glegroups.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        wsd_upstream <wsd_upstream@...iatek.com>,
        <linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH v4 1/2] kasan: detect negative size in memory operation
 function

On Thu, 2019-11-21 at 16:03 +0300, Andrey Ryabinin wrote:
> 
> On 11/21/19 4:02 PM, Walter Wu wrote:
> > On Thu, 2019-11-21 at 15:26 +0300, Andrey Ryabinin wrote:
> >>
> >> On 11/12/19 9:53 AM, Walter Wu wrote:
> >>
> >>> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> >>> index 6814d6d6a023..4bfce0af881f 100644
> >>> --- a/mm/kasan/common.c
> >>> +++ b/mm/kasan/common.c
> >>> @@ -102,7 +102,8 @@ EXPORT_SYMBOL(__kasan_check_write);
> >>>  #undef memset
> >>>  void *memset(void *addr, int c, size_t len)
> >>>  {
> >>> -	check_memory_region((unsigned long)addr, len, true, _RET_IP_);
> >>> +	if (!check_memory_region((unsigned long)addr, len, true, _RET_IP_))
> >>> +		return NULL;
> >>>  
> >>>  	return __memset(addr, c, len);
> >>>  }
> >>> @@ -110,8 +111,9 @@ void *memset(void *addr, int c, size_t len)
> >>>  #undef memmove
> >>>  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_);
> >>> +	if (!check_memory_region((unsigned long)src, len, false, _RET_IP_) ||
> >>> +	    !check_memory_region((unsigned long)dest, len, true, _RET_IP_))
> >>> +		return NULL;
> >>>  
> >>>  	return __memmove(dest, src, len);
> >>>  }
> >>> @@ -119,8 +121,9 @@ void *memmove(void *dest, const void *src, size_t len)
> >>>  #undef memcpy
> >>>  void *memcpy(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_);
> >>> +	if (!check_memory_region((unsigned long)src, len, false, _RET_IP_) ||
> >>> +	    !check_memory_region((unsigned long)dest, len, true, _RET_IP_))
> >>> +		return NULL;
> >>>  
> >>
> >> I realized that we are going a wrong direction here. Entirely skipping mem*() operation on any
> >> poisoned shadow value might only make things worse. Some bugs just don't have any serious consequences,
> >> but skipping the mem*() ops entirely might introduce such consequences, which wouldn't happen otherwise.
> >>
> >> So let's keep this code as this, no need to check the result of check_memory_region().
> >>
> >>
> > Ok, we just need to determine whether size is negative number. If yes
> > then KASAN produce report and continue to execute mem*(). right?
> > 
> 
> Yes.

Thanks for your suggestion.
I will send a new v5 patch tomorrow.

Walter