linux-kernel - Re: [PATCH v2] dns_resolver: assure that dns

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Date:	Sun, 08 Jun 2014 01:57:44 +0400
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	Manuel Schölling <manuel.schoelling@....de>
CC:	David Rientjes <rientjes@...gle.com>, davem@...emloft.net,
	jeffrey.t.kirsher@...el.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] dns_resolver: assure that dns_query() result is null-terminated

On 06/08/2014 01:42 AM, David Rientjes wrote:

>> dns_query() credulously assumes that keys are null-terminated and
>> returns a copy of a memory block that is off by one.

> No sign-off?  Please read Documentation/SubmittingPatches.

>> ---
>>   net/dns_resolver/dns_query.c |    4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/net/dns_resolver/dns_query.c b/net/dns_resolver/dns_query.c
>> index e7b6d53..84871a2 100644
>> --- a/net/dns_resolver/dns_query.c
>> +++ b/net/dns_resolver/dns_query.c
>> @@ -145,11 +145,11 @@ int dns_query(const char *type, const char *name, size_t namelen,
>>   	len = upayload->datalen;
>>
>>   	ret = -ENOMEM;
>> -	*_result = kmalloc(len + 1, GFP_KERNEL);
>> +	*_result = kzalloc(len + 1, GFP_KERNEL);
>>   	if (!*_result)
>>   		goto put;
>>
>> -	memcpy(*_result, upayload->data, len + 1);
>> +	memcpy(*_result, upayload->data, len);
>>   	if (_expiry)
>>   		*_expiry = rkey->expiry;

> kzalloc() would be unnecessary overhead (zeroing definitely comes with a
> cost) if you're going to copy to the memory immediately afterwards.  Just
> leave the kmalloc(), do the memcpy() and explicitly zero terminate it
> _result.

    You can also replace kmalloc()/memcpy() with kmemdup().

WBR, Sergei

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