Milter-greylist

Dietmar Rieder <adrieder@...> wrote:

>             libumem.so.1`malloc+0x23
>                   libresolv.so.2`__res_vinit+0x118
>                   libresolv.so.2`res_ninit+0x1a
>                   dnsrbl_check_source+0x14a

A quick look at NetBSD's res_ninit() sources (it's from BIND, and I
beleive most system have the same), indeed shows a malloc():
    statp->_u._ext.ext = malloc(sizeof(*statp->_u._ext.ext));

This means that any successful call to res_ninit() must have a
corresponding res_ndestroy() call.

In dnsrbl_check_source, once res_ninit() is called, there is no way out
of the function without executing res_ndestroy(). But the trick is that
res_ninit() and res_ndestroy() may be macros in milter-greylist, so that
we can cope with older BIND resolvers without having #ifdef's everywhere
in our code.

In some situation,  milter-greylist can define res_ndestroy() as
res_nclose(), and this is a problem, because at least in NetBSD's
resolver, res_ndestroy() does free statp->_u._ext.ext  whereas
res_nclose() does not.

Hence, here is the offending code in dnsrbl.c

#if (defined(res_ninit) || (__RES >= 19991006) )
#define HAVE_RESN       1
#ifndef res_ndestroy
#define res_ndestroy(res)       res_nclose(res)   /* <--- XXXhereXXX */
#endif
#else   
#define res_ninit(res) \
        ((_res.options & RES_INIT) == 0 && res_init())
#define res_nquery(res, req, class, type, ans, anslen)  \
        res_query(req, class, type, ans, anslen)
#define res_ndestroy(res)
#endif  

The ifdef on res_ninit and res_ndestroy is an error, it will never be
evaluated as true. Please try this instead, and tell us if you get the
warning at compile time.

#if (__RES >= 19991006) )
#define HAVE_RESN       1
#else   
#warn "no res_ninit!"
#define res_ninit(res) \
        ((_res.options & RES_INIT) == 0 && res_init())
#define res_nquery(res, req, class, type, ans, anslen)  \
        res_query(req, class, type, ans, anslen)
#define res_ndestroy(res)
#endif  

Handling the BIND versions where res_nclose() exists but not
res_ndestroy() must be done by an autoconf test.

-- 
Emmanuel Dreyfus
http://hcpnet.free.fr/pubz
manu@...