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

[Pablo Neira Ayuso <pablo@netfilter.org>]

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;
> >>--
> >>1.7.10.4de
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