linux-kernel - Re: [PATCH] RDMA/hns: Use 64-bit arithmetic instead of 32-bit

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Date:   Mon, 22 Oct 2018 20:22:06 +0200
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     Lijun Ou <oulijun@...wei.com>,
        "Wei Hu(Xavier)" <xavier.huwei@...wei.com>,
        Doug Ledford <dledford@...hat.com>, linux-rdma@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] RDMA/hns: Use 64-bit arithmetic instead of 32-bit



On 10/22/18 8:15 PM, Jason Gunthorpe wrote:
> On Thu, Oct 18, 2018 at 10:02:58AM +0200, Gustavo A. R. Silva wrote:
>> Cast *max_num_sg* to u64 in order to give the compiler complete
>> information about the proper arithmetic to use.
>>
>> Notice that such variable is used in a context that expects an
>> expression of type u64 (64 bits, unsigned) and the following
>> expression is currently being evaluated using 32-bit
>> arithmetic:
>>
>> length = max_num_sg * page_size;
>>
>> Addresses-Coverity-ID: 1474517 ("Unintentional integer overflow")
>> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
>>  drivers/infiniband/hw/hns/hns_roce_mr.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/infiniband/hw/hns/hns_roce_mr.c b/drivers/infiniband/hw/hns/hns_roce_mr.c
>> index 521ad2a..d479d5e 100644
>> +++ b/drivers/infiniband/hw/hns/hns_roce_mr.c
>> @@ -1219,7 +1219,7 @@ struct ib_mr *hns_roce_alloc_mr(struct ib_pd *pd, enum ib_mr_type mr_type,
>>  	int ret;
>>  
>>  	page_size = 1 << (hr_dev->caps.pbl_buf_pg_sz + PAGE_SHIFT);
>> -	length = max_num_sg * page_size;
>> +	length = (u64)max_num_sg * page_size;
> 
> This should be done with check_mul_overflow() which will also force
> the input types to the correct thing.
> 

Yep, you're right. That's part of the new API for checking overflows.

I'll use that macro.

> alloc_mr is callable from userspace so the potential overflow here
> should not be ignored.
> 

Thanks for the feedback.
--
Gustavo