Re: [PATCH] block: fix get_max_segment_size() overflow on 32bit arch

[Jens Axboe <axboe@kernel.dk>]

On 1/7/20 7:06 PM, Damien Le Moal wrote:
> On 2020/01/08 10:25, Ming Lei wrote:
>> Commit 429120f3df2d starts to take account of segment's start dma address
>> when computing max segment size, and data type of 'unsigned long'
>> is used to do that. However, the segment mask may be 0xffffffff, so
>> the figured out segment size may be overflowed because DMA address can
>> be 64bit on 32bit arch.
>>
>> Fixes the issue by using 'unsigned long long' to compute max segment
>> size.
>>
>> Fixes: 429120f3df2d ("block: fix splitting segments on boundary masks")
>> Reported-by: Guenter Roeck <linux@roeck-us.net>
>> Tested-by: Guenter Roeck <linux@roeck-us.net>
>> Signed-off-by: Ming Lei <ming.lei@redhat.com>
>> ---
>>  block/blk-merge.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/block/blk-merge.c b/block/blk-merge.c
>> index 347782a24a35..b0fcc72594cb 100644
>> --- a/block/blk-merge.c
>> +++ b/block/blk-merge.c
>> @@ -159,12 +159,12 @@ static inline unsigned get_max_io_size(struct request_queue *q,
>>  
>>  static inline unsigned get_max_segment_size(const struct request_queue *q,
>>  					    struct page *start_page,
>> -					    unsigned long offset)
>> +					    unsigned long long offset)
>>  {
>>  	unsigned long mask = queue_segment_boundary(q);
>>  
>>  	offset = mask & (page_to_phys(start_page) + offset);
> 
> Shouldn't mask be an unsigned long long too for this to give the
> expected correct result ?

Don't think so, and the seg boundary is a ulong to begin with as well.

-- 
Jens Axboe