Re: Register leak in libpcap 0.9.7

["Bruce Keats" <brucekeats () gmail com>]

That was fast!  Thanks Guy.

I will give it a try.

Bruce

On Fri, Jun 13, 2008 at 4:17 PM, Guy Harris <guy () alum mit edu> wrote:

> Bruce Keats wrote:
>
> > I have a program that is listening on a radio tap interface that is using
> > libpcap.  It occasionally changes the BPF something like "ether host
> > xx:xx:xx:xx:xx:xx".
>
> ...which presumably means it calls pcap_compile() more than once.
>
>  Is there a fix for this issue?
> >
>
> Yes:
>
>  revision 1.291
> > date: 2007-10-26 00:44:56 +0000;  author: guy;  state: Exp;  lines: +13 -1
> > Re-initialize the table of used registers, and the current register,
> > before compiling an expression; pcap_compile() can be called more than
> > once, and some registers can now be allocated and not freed in the
> > process of code generation (for example, the register allocated to hold
> > the length of a radiotap header, which can't be freed until we're
> > finished generating all the code).
>
> but it's not in any current releases of libpcap.  I've attached a patch
> that should apply to 0.9.7's gencode.c.
>
> Index: gencode.c
> ===================================================================
> RCS file: /tcpdump/master/libpcap/gencode.c,v
> retrieving revision 1.290
> retrieving revision 1.291
> diff -c -r1.290 -r1.291
> *** gencode.c   5 Oct 2007 01:40:14 -0000       1.290
> --- gencode.c   26 Oct 2007 00:44:56 -0000      1.291
> ***************
> *** 134,139 ****
> --- 134,140 ----
>
>  static void init_linktype(pcap_t *);
>
> + static void init_regs(void);
>  static int alloc_reg(void);
>  static void free_reg(int);
>
> ***************
> *** 369,374 ****
> --- 370,376 ----
>        n_errors = 0;
>        root = NULL;
>        bpf_pcap = p;
> +       init_regs();
>        if (setjmp(top_ctx)) {
>                lex_cleanup();
>                freechunks();
> ***************
> *** 6045,6050 ****
> --- 6047,6062 ----
>  static int curreg;
>
>  /*
> +  * Initialize the table of used registers and the current register.
> +  */
> + static void
> + init_regs()
> + {
> +       curreg = 0;
> +       memset(regused, 0, sizeof regused);
> + }
> +
> + /*
>   * Return the next free register.
>   */
>  static int
>
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