netdev - Re: [PATCH] Net: rxrpc: signed and unsigned issue, need type cast for n

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Date:	Tue, 23 Apr 2013 09:24:48 +0800
From:	Chen Gang <gang.chen@...anux.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
CC:	David Miller <davem@...emloft.net>,
	"dhowells@...hat.com" <dhowells@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] Net: rxrpc: signed and unsigned issue, need type cast
 for n_elem.

On 2013年04月23日 03:34, Ben Hutchings wrote:
> On Mon, 2013-04-22 at 18:24 +0800, Chen Gang wrote:
>> n_elem is unsigned int which never < 0.
>>   but it seems, we realy need check it whether < 0.
>>   so need a type cast for it.
>>
>>   find it by EXTRA_CFLAGS=-W
>>
>>
>> Signed-off-by: Chen Gang <gang.chen@...anux.com>
>> ---
>>  net/rxrpc/ar-key.c |    2 +-
>>  1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/net/rxrpc/ar-key.c b/net/rxrpc/ar-key.c
>> index 7633a75..ba0b722 100644
>> --- a/net/rxrpc/ar-key.c
>> +++ b/net/rxrpc/ar-key.c
>> @@ -346,7 +346,7 @@ static int rxrpc_krb5_decode_tagged_array(struct krb5_tagged_data **_td,
>>  
>>  	n_elem = ntohl(*xdr++);
>>  	toklen -= 4;
>> -	if (n_elem < 0 || n_elem > max_n_elem)
>> +	if ((int)n_elem < 0 || n_elem > max_n_elem)
> 
> (int)n_elem < 0 is equivalent to n_elem >= 0x80000000, and if that is
> true then n_elem > max_n_elem (because max_n_elem <= 0xff).
> 

  ok, thanks, my subject and the comments are incorrect.

  but I still prefer to improve the original code like below.
    (also need change the subject and the comments)

----------------------diff begin------------------------------------------------

diff --git a/net/rxrpc/ar-key.c b/net/rxrpc/ar-key.c
index 7633a75..cde682f 100644
--- a/net/rxrpc/ar-key.c
+++ b/net/rxrpc/ar-key.c
@@ -346,7 +346,7 @@ static int rxrpc_krb5_decode_tagged_array(struct krb5_tagged_data **_td,
 
 	n_elem = ntohl(*xdr++);
 	toklen -= 4;
-	if (n_elem < 0 || n_elem > max_n_elem)
+	if (n_elem > max_n_elem)
 		return -EINVAL;
 	*_n_elem = n_elem;
 	if (n_elem > 0) {

----------------------diff end--------------------------------------------------

> Ben.
> 
>>  		return -EINVAL;
>>  	*_n_elem = n_elem;
>>  	if (n_elem > 0) {
> 


-- 
Chen Gang

Asianux Corporation
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