linux-kernel - Re: [PATCH v2] tipc: Avoid copying bytes beyond the supplied data

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Message-ID: <00ce1b1e52ac4b729d982c86127334aa@svr-chch-ex1.atlnz.lc>
Date:   Wed, 22 May 2019 20:46:13 +0000
From:   Chris Packham <Chris.Packham@...iedtelesis.co.nz>
To:     Ying Xue <ying.xue@...driver.com>,
        "jon.maloy@...csson.com" <jon.maloy@...csson.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "niveditas98@...il.com" <niveditas98@...il.com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "tipc-discussion@...ts.sourceforge.net" 
        <tipc-discussion@...ts.sourceforge.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] tipc: Avoid copying bytes beyond the supplied data

Hi Ying,

On 22/05/19 7:58 PM, Ying Xue wrote:
> On 5/20/19 11:45 AM, Chris Packham wrote:
>> TLV_SET is called with a data pointer and a len parameter that tells us
>> how many bytes are pointed to by data. When invoking memcpy() we need
>> to careful to only copy len bytes.
>>
>> Previously we would copy TLV_LENGTH(len) bytes which would copy an extra
>> 4 bytes past the end of the data pointer which newer GCC versions
>> complain about.
>>
>>   In file included from test.c:17:
>>   In function 'TLV_SET',
>>       inlined from 'test' at test.c:186:5:
>>   /usr/include/linux/tipc_config.h:317:3:
>>   warning: 'memcpy' forming offset [33, 36] is out of the bounds [0, 32]
>>   of object 'bearer_name' with type 'char[32]' [-Warray-bounds]
>>       memcpy(TLV_DATA(tlv_ptr), data, tlv_len);
>>       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>   test.c: In function 'test':
>>   test.c::161:10: note:
>>   'bearer_name' declared here
>>       char bearer_name[TIPC_MAX_BEARER_NAME];
>>            ^~~~~~~~~~~
>>
>> We still want to ensure any padding bytes at the end are initialised, do
>> this with a explicit memset() rather than copy bytes past the end of
>> data. Apply the same logic to TCM_SET.
>>
>> Signed-off-by: Chris Packham <chris.packham@...iedtelesis.co.nz>
> 
> Acked-by: Ying Xue <ying.xue@...driver.com>
> 
> 
> But please make the same changes in usr/include/linux/tipc_config.h
> 

I don't understand this comment. There is no usr/include in the kernel 
source.

On most distros that is generated from include/uapi in the kernel source 
and packaged as part of libc or a kernel-headers package. So once this 
patch is accepted and makes it into the distros 
/usr/include/linux/tipc_config.h will have this fix.

Adding Cc: stable might help get it there sooner. But I wanted to get it 
reviewed/accepted first.

>> ---
>>
>> Changes in v2:
>> - Ensure padding bytes are initialised in both TLV_SET and TCM_SET
>>
>>   include/uapi/linux/tipc_config.h | 10 +++++++---
>>   1 file changed, 7 insertions(+), 3 deletions(-)
>>
>> diff --git a/include/uapi/linux/tipc_config.h b/include/uapi/linux/tipc_config.h
>> index 4b2c93b1934c..4955e1a9f1bc 100644
>> --- a/include/uapi/linux/tipc_config.h
>> +++ b/include/uapi/linux/tipc_config.h
>> @@ -307,8 +307,10 @@ static inline int TLV_SET(void *tlv, __u16 type, void *data, __u16 len)
>>   	tlv_ptr = (struct tlv_desc *)tlv;
>>   	tlv_ptr->tlv_type = htons(type);
>>   	tlv_ptr->tlv_len  = htons(tlv_len);
>> -	if (len && data)
>> -		memcpy(TLV_DATA(tlv_ptr), data, tlv_len);
>> +	if (len && data) {
>> +		memcpy(TLV_DATA(tlv_ptr), data, len);
>> +		memset(TLV_DATA(tlv_ptr) + len, 0, TLV_SPACE(len) - tlv_len);
>> +	}
>>   	return TLV_SPACE(len);
>>   }
>>   
>> @@ -405,8 +407,10 @@ static inline int TCM_SET(void *msg, __u16 cmd, __u16 flags,
>>   	tcm_hdr->tcm_len   = htonl(msg_len);
>>   	tcm_hdr->tcm_type  = htons(cmd);
>>   	tcm_hdr->tcm_flags = htons(flags);
>> -	if (data_len && data)
>> +	if (data_len && data) {
>>   		memcpy(TCM_DATA(msg), data, data_len);
>> +		memset(TCM_DATA(msg) + data_len, 0, TCM_SPACE(data_len) - msg_len);
>> +	}
>>   	return TCM_SPACE(data_len);
>>   }
>>   
>>
>