[Ocfs2-devel] [PATCH] ocfs2: Fix memory overflow in cow_by_page.

[Tao Ma]

Joel Becker wrote:
> On Thu, Jan 21, 2010 at 02:59:26PM +0800, Tao Ma wrote:
>> In ocfs2_duplicate_clusters_by_page, we calculate map_end
>> by shifting page_index. But actually in case we meet with
>> a large offset(say in a i686 box, poff_t is only 32 bits
>> and page_index=2056240), we will overflow. So change it
>> by adding PAGE_CACHE_SIZE to offset.
>>
>> Signed-off-by: Tao Ma <tao.ma at oracle.com>
>> ---
>>  fs/ocfs2/refcounttree.c |    2 +-
>>  1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/fs/ocfs2/refcounttree.c b/fs/ocfs2/refcounttree.c
>> index 74db2be..6db863d 100644
>> --- a/fs/ocfs2/refcounttree.c
>> +++ b/fs/ocfs2/refcounttree.c
>> @@ -2945,7 +2945,7 @@ static int ocfs2_duplicate_clusters_by_page(handle_t *handle,
>>  
>>  	while (offset < end) {
>>  		page_index = offset >> PAGE_CACHE_SHIFT;
>> -		map_end = (page_index + 1) << PAGE_CACHE_SHIFT;
>> +		map_end = offset + PAGE_CACHE_SIZE;
> 
> 	First, we can't be computing by offset, because map_end is
> supposed to be page bounded, right?  Also, what if we have an offset
> that is the last page possible?  Won't that wrap as well, setting
> map_end to 0?
> 	Why aren't we computing map_end like we compute end, as a loff_t
> value?
> 
>   		page_index = offset >> PAGE_CACHE_SHIFT;
> - 		map_end = (page_index + 1) << PAGE_CACHE_SHIFT;
> + 		map_end = ((loff_t)page_index + 1) << PAGE_CACHE_SHIFT;
> 
>   		if (map_end > end)
>   			map_end = end;
> 
> The map_end>end check will catch anything too big.
oh, you are right.
I only considered the problem of overflow, but forget the original 
usage. Sorry.

Regards,
Tao