Re: [dpdk-dev] [PATCH v2] lib/cfgfile: replace strcat with strlcat

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 3/26/2019 10:04 AM, Chaitanya Babu, TalluriX wrote:
> Hi 
> 
>> -----Original Message-----
>> From: Yigit, Ferruh
>> Sent: Friday, March 8, 2019 11:01 PM
>> To: Richardson, Bruce <bruce.richardson@intel.com>; Chaitanya Babu, TalluriX
>> <tallurix.chaitanya.babu@intel.com>
>> Cc: dev@dpdk.org; Pattan, Reshma <reshma.pattan@intel.com>;
>> Parthasarathy, JananeeX M <jananeex.m.parthasarathy@intel.com>;
>> Dumitrescu, Cristian <cristian.dumitrescu@intel.com>; stable@dpdk.org
>> Subject: Re: [PATCH v2] lib/cfgfile: replace strcat with strlcat
>>
>> On 3/8/2019 2:02 PM, Bruce Richardson wrote:
>>> On Fri, Mar 08, 2019 at 12:45:50PM +0000, Chaitanya Babu Talluri wrote:
>>>> Replace strcat with strlcat to avoid buffer overflow.
>>>>
>>>> Fixes: a6a47ac9c2 ("cfgfile: rework load function")
>>>> Cc: stable@dpdk.org
>>>>
>>>> Signed-off-by: Chaitanya Babu Talluri
>>>> <tallurix.chaitanya.babu@intel.com>
>>>> ---
>>>> v2: Instead of strcat, used strlcat.
>>>> ---
>>>>  lib/librte_cfgfile/rte_cfgfile.c | 4 +++-
>>>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/lib/librte_cfgfile/rte_cfgfile.c
>>>> b/lib/librte_cfgfile/rte_cfgfile.c
>>>> index 7d8c941ea..3296bb6f8 100644
>>>> --- a/lib/librte_cfgfile/rte_cfgfile.c
>>>> +++ b/lib/librte_cfgfile/rte_cfgfile.c
>>>> @@ -8,6 +8,7 @@
>>>>  #include <ctype.h>
>>>>  #include <errno.h>
>>>>  #include <rte_common.h>
>>>> +#include <rte_string_fns.h>
>>>>
>>>>  #include "rte_cfgfile.h"
>>>>
>>>> @@ -224,10 +225,11 @@ rte_cfgfile_load_with_params(const char
>> *filename, int flags,
>>>>  			_strip(split[1], strlen(split[1]));
>>>>  			char *end = memchr(split[1], '\\', strlen(split[1]));
>>>>
>>>> +			size_t split_len = strlen(split[1]) + 1;
>>>>  			while (end != NULL) {
>>>>  				if (*(end+1) == params->comment_character)
>> {
>>>>  					*end = '\0';
>>>> -					strcat(split[1], end+1);
>>>> +					strlcat(split[1], end+1, split_len);
>>>
>>> I don't think this will do what you want. Remember that strlcat takes
>>> the total length of the buffer, which means that if split_len is set
>>> to the current length (as you do before the while statement), then
>>> passing that as the length parameter will cause strlcat to do nothing,
>>> since it sees the buffer as already full.
>>
>> The logic doesn't lengthen the 'split[1]' content, indeed it reduces the initial
>> size although it uses string concatenation, that is why it should be OK to use
>> 'split_len' here.
>>
>> What code does is, it finds specific char in 'split' buffer and removes it by
>> shifting remaining chars one byte to the left. So it shouldn't pass the initial size
>> of the buffer.
>>
>> There is a overlapping strings concern, which 'strcat' & 'strlcat' don't support,
>> but I guess it is OK here since we are sure that strings are separated by a
>> NULL, so where a char read and written should be different although overall
>> dst and src buffers overlap.
> 
> Yes, although the same string is manipulated the split string (*end = '\0') is separated with NULL.
> Strlcat works fine here and expected concatenation  is happening.
> If there are no further comments request for ACK please.

Acked-by: Ferruh Yigit <ferruh.yigit@intel.com>