Re: [PATCH] CVE-2016-3075: Stack overflow in _nss_dns_getnetbyname_r [BZ #19879]

[Carlos O'Donell <carlos at redhat dot com>]

On 03/29/2016 07:01 AM, Florian Weimer wrote:
> This is a minor security issue in nss_dns, triggered by a very long name
> passed to getnetbyname.
> 
> The defensive copy is not needed because the name may not alias the
> output buffer.

This code dates back to the original 1996 sources that were included in glibc
and I expect that at that point the propagation of `const char *` for name
was not entirely complete and that at some point the internals assumed they
could scribble on name. That is not the case today, we propagate `const char *`
to all callers, and a rather deep review that I just did using ctags shows
that the call tree preserves the constness of name.

This patch looks good to me.

> 2016-03-29  Florian Weimer  <fweimer@redhat.com>
> 
> 	[BZ #19879]
> 	CVE-2016-3075
> 	* resolv/nss_dns/dns-network.c (_nss_dns_getnetbyname_r): Do not
> 	copy name.
> 
> diff --git a/resolv/nss_dns/dns-network.c b/resolv/nss_dns/dns-network.c
> index 2eb2f67..8f301a7 100644
> --- a/resolv/nss_dns/dns-network.c
> +++ b/resolv/nss_dns/dns-network.c
> @@ -118,17 +118,14 @@ _nss_dns_getnetbyname_r (const char *name, struct netent *result,
>    } net_buffer;
>    querybuf *orig_net_buffer;
>    int anslen;
> -  char *qbuf;
>    enum nss_status status;
>  
>    if (__res_maybe_init (&_res, 0) == -1)
>      return NSS_STATUS_UNAVAIL;
>  
> -  qbuf = strdupa (name);
> -
>    net_buffer.buf = orig_net_buffer = (querybuf *) alloca (1024);
>  
> -  anslen = __libc_res_nsearch (&_res, qbuf, C_IN, T_PTR, net_buffer.buf->buf,
> +  anslen = __libc_res_nsearch (&_res, name, C_IN, T_PTR, net_buffer.buf->buf,
>  			       1024, &net_buffer.ptr, NULL, NULL, NULL, NULL);
>    if (anslen < 0)
>      {
	

-- 
Cheers,
Carlos.