Re: [libnftnl PATCH] mxml: test if the root node name is initialized before to compare it.

["Álvaro Neira Ayuso" <alvaroneay@gmail.com>]

El 04/03/15 a las 20:20, Pablo Neira Ayuso escribió:
> On Wed, Mar 04, 2015 at 08:03:18PM +0100, Pablo Neira Ayuso wrote:
>> On Tue, Mar 03, 2015 at 02:45:34PM +0100, Álvaro Neira Ayuso wrote:
>>> El 03/03/15 a las 00:35, Pablo Neira Ayuso escribió:
>>>> On Mon, Mar 02, 2015 at 08:58:38PM +0100, Alvaro Neira Ayuso wrote:
>>>>> If the root node name is not correctly initialized, we have a crash.
>>>>
>>>> Under what circunstances may tree->value.opaque be NULL?
>>>
>>> The function mxmlLoadFile doesn't work correctly. With my patch to
>>> import ruleset in json and xml. I have seen that if we use a ruleset
>>> in json and use the command nft import xml.
>>
>> OK, so this bug can be triggered by malformed input.
>>
>>> The function mxmlLoadFile returns a tree without any information
>>> inside.  Therefore, when we try to verify that the name of the first
>>> node is the same of the parameter, we have a crash.
>>>
>>> We have two ways to solve it. Test if the node is NULL and:
>>>   1- show an error that the node is not found.
>>>   2- show an error that the input is not correctly.
>>>
>>> I have thought that the best is the first. But I can change it.
>>
>> I think we have to make robust checks on the input, if what we get is
>> not "sane" then it's not worth going further.
>>
>> So I'd suggest you modify this lines a bit below:
>>
>>          if (tree->value.opaque == NULL) {
>>                  err->error = NFT_PARSE_EBADINPUT;
>>                  goto err;
>>          }
>>
>> to look like:
>>
>>          if (tree == NULL || tree->value.opaque == NULL) {
>>                  err->error = NFT_PARSE_EBADINPUT;
>>                  goto err;
>>          }
>>
>>>>> ---
>>>>>   src/mxml.c |    3 ++-
>>>>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/src/mxml.c b/src/mxml.c
>>>>> index 0001ba0..b68f86f 100644
>>>>> --- a/src/mxml.c
>>>>> +++ b/src/mxml.c
>>>>> @@ -43,7 +43,8 @@ mxml_node_t *nft_mxml_build_tree(const void *data, const char *treename,
>>>>>   		goto err;
>>>>>   	}
>>>>>
>>>>> -	if (strcmp(tree->value.opaque, treename) == 0)
>>>>> +	if (tree->value.opaque != NULL &&
>>>>> +	    strcmp(tree->value.opaque, treename) == 0)
>>>>>   		return tree;
>>>>>
>>>>>   	err->error = NFT_PARSE_EMISSINGNODE;
>
> Actually your patch looks correct because you're returning "missing
> node" which is triggering the crash, right?

Yes, the first node of the tree is missing and we have a crash.

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