Re: [PATCH] SUNRPC: fix copying of multiple pages in gss_read_proxy_verf()

[Martijn de Gouw]

Hi

On 19-10-2020 17:23, J. Bruce Fields wrote:
> On Mon, Oct 19, 2020 at 01:42:27PM +0200, Martijn de Gouw wrote:
>> When the passed token is longer than 4032 bytes, the remaining part
>> of the token must be copied from the rqstp->rq_arg.pages. But the
>> copy must make sure it happens in a consecutive way.
> 
> Thanks.  Apologies, but I don't immediately see where the copy is
> non-consecutive.  What exactly is the bug in the existing code?

In the first memcpy 'length' bytes are copied from argv->iobase, but 
since the header is in front, this never fills the whole first page of 
in_token->pages.

The memcpy in the loop copies the following bytes, but starts writing at 
the next page of in_token->pages. This leaves the last bytes of page 0 
unwritten.

Next to that, the remaining data is in page 0 of rqstp->rq_arg.pages, 
not page 1.

Regards, Martijn

> 
> --b.
> 
>>
>> Signed-off-by: Martijn de Gouw <martijn.de.gouw@xxxxxxxxxxxxxxxxxxxxxxxxx>
>> ---
>>   net/sunrpc/auth_gss/svcauth_gss.c | 27 +++++++++++++++++----------
>>   1 file changed, 17 insertions(+), 10 deletions(-)
>>
>> diff --git a/net/sunrpc/auth_gss/svcauth_gss.c b/net/sunrpc/auth_gss/svcauth_gss.c
>> index 258b04372f85..bd4678db9d76 100644
>> --- a/net/sunrpc/auth_gss/svcauth_gss.c
>> +++ b/net/sunrpc/auth_gss/svcauth_gss.c
>> @@ -1147,9 +1147,9 @@ static int gss_read_proxy_verf(struct svc_rqst *rqstp,
>>   			       struct gssp_in_token *in_token)
>>   {
>>   	struct kvec *argv = &rqstp->rq_arg.head[0];
>> -	unsigned int page_base, length;
>> -	int pages, i, res;
>> -	size_t inlen;
>> +	unsigned int length, pgto_offs, pgfrom_offs;
>> +	int pages, i, res, pgto, pgfrom;
>> +	size_t inlen, to_offs, from_offs;
>>   
>>   	res = gss_read_common_verf(gc, argv, authp, in_handle);
>>   	if (res)
>> @@ -1177,17 +1177,24 @@ static int gss_read_proxy_verf(struct svc_rqst *rqstp,
>>   	memcpy(page_address(in_token->pages[0]), argv->iov_base, length);
>>   	inlen -= length;
>>   
>> -	i = 1;
>> -	page_base = rqstp->rq_arg.page_base;
>> +	to_offs = length;
>> +	from_offs = rqstp->rq_arg.page_base;
>>   	while (inlen) {
>> -		length = min_t(unsigned int, inlen, PAGE_SIZE);
>> -		memcpy(page_address(in_token->pages[i]),
>> -		       page_address(rqstp->rq_arg.pages[i]) + page_base,
>> +		pgto = to_offs >> PAGE_SHIFT;
>> +		pgfrom = from_offs >> PAGE_SHIFT;
>> +		pgto_offs = to_offs & ~PAGE_MASK;
>> +		pgfrom_offs = from_offs & ~PAGE_MASK;
>> +
>> +		length = min_t(unsigned int, inlen,
>> +			 min_t(unsigned int, PAGE_SIZE - pgto_offs,
>> +			       PAGE_SIZE - pgfrom_offs));
>> +		memcpy(page_address(in_token->pages[pgto]) + pgto_offs,
>> +		       page_address(rqstp->rq_arg.pages[pgfrom]) + pgfrom_offs,
>>   		       length);
>>   
>> +		to_offs += length;
>> +		from_offs += length;
>>   		inlen -= length;
>> -		page_base = 0;
>> -		i++;
>>   	}
>>   	return 0;
>>   }
>> -- 
>> 2.20.1

-- 
Martijn de Gouw
Designer
Prodrive Technologies
Mobile: +31 63 17 76 161
Phone:  +31 40 26 76 200