[lxc-devel] [PATCH] hwaddr templating (with fixes from comments)

[Serge Hallyn]

Quoting lxc at zitta.fr (lxc at zitta.fr):
> This change introduce mac address templating.
> 
> By setting lxc.network.hwaddr to something like fe:xx:xx:xx:xx:xx
> each "x" will be replaced by a random value.
> If less significant bit of first byte is "templated", it will be
> set to 0.
> 
> This change introduce also a common randinit() function that could be
> used to initialize random generator.
> 
> Signed-off-by: gza <lxc at zitta.fr>

Sorry, two more changes needed.  If you prefer I can do them
in-line.

1. strdup value needs to be checked in case it's NULL.

2. rand() is not thread-safe.  Better to use rand_r().  I'm not
sure that it's all *that* important as I don't think anything
will misbehave as a result, but it's worth switching.

> ---
>  doc/lxc.conf.sgml.in |  4 +++-
>  src/lxc/confile.c    | 41 ++++++++++++++++++++++++++++++++++++++---
>  src/lxc/utils.c      | 18 ++++++++++++++++++
>  src/lxc/utils.h      |  2 ++
>  4 files changed, 61 insertions(+), 4 deletions(-)
> 
> diff --git a/doc/lxc.conf.sgml.in b/doc/lxc.conf.sgml.in
> index e6d9689..4bbeeeb 100644
> --- a/doc/lxc.conf.sgml.in
> +++ b/doc/lxc.conf.sgml.in
> @@ -326,7 +326,9 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor,
> Boston, MA 02110-1301 USA
>            the interface mac address is dynamically allocated by
>            default to the virtual interface, but in some cases,
>            this is needed to resolve a mac address conflict or to
> -          always have the same link-local ipv6 address
> +          always have the same link-local ipv6 address.
> +          Any "x" in address will be replaced by random value,
> +          this allows setting hwaddr templates.
>          </para>
>        </listitem>
>      </varlistentry>
> diff --git a/src/lxc/confile.c b/src/lxc/confile.c
> index 0982b3e..c83c5bf 100644
> --- a/src/lxc/confile.c
> +++ b/src/lxc/confile.c
> @@ -508,6 +508,28 @@ static int macvlan_mode(int *valuep, const char *value)
>      return -1;
>  }
>  
> +static int rand_complete_hwaddr(char *hwaddr)
> +{
> +    const char hex[] = "0123456789abcdef";
> +    char *curs = hwaddr;
> +
> +    randinit();
> +
> +    while (*curs != '\0')
> +    {
> +        if ( *curs == 'x' || *curs == 'X' ) {
> +            if (curs - hwaddr == 1) {
> +                //ensure address is unicast
> +                *curs = hex[(rand() & 0x0E)];
> +            } else {
> +                *curs = hex[rand() & 0x0F];
> +            }
> +        }
> +        curs++;
> +    }
> +    return 0;
> +}
> +
>  static int config_network_flags(const char *key, const char *value,
>                  struct lxc_conf *lxc_conf)
>  {
> @@ -575,11 +597,24 @@ static int config_network_hwaddr(const char *key,
> const char *value,
>  {
>      struct lxc_netdev *netdev;
>  
> -    netdev = network_netdev(key, value, &lxc_conf->network);
> -    if (!netdev)
> +    char *newval = strdup(value);
> +
> +    rand_complete_hwaddr(newval);
> +
> +    netdev = network_netdev(key, newval, &lxc_conf->network);
> +    if (!netdev) {
> +        free(newval);
>          return -1;
> +    };
>  
> -    return config_string_item(&netdev->hwaddr, value);
> +    if (!newval || strlen(newval) == 0) {
> +        free(newval);
> +        netdev->hwaddr = NULL;
> +        return 0;
> +    }
> +
> +    netdev->hwaddr = newval;
> +    return 0;
>  }
>  
>  static int config_network_vlan_id(const char *key, const char *value,
> diff --git a/src/lxc/utils.c b/src/lxc/utils.c
> index 1f9ceea..0451a1d 100644
> --- a/src/lxc/utils.c
> +++ b/src/lxc/utils.c
> @@ -1108,3 +1108,21 @@ void **lxc_append_null_to_array(void **array,
> size_t count)
>      }
>      return array;
>  }
> +
> +void randinit(void)
> +{
> +    /*
> +    srand pre-seed function based on /dev/urandom
> +    */
> +    FILE *f;
> +    f = fopen("/dev/urandom", "r");
> +    if (f) {
> +        unsigned int seed;
> +        int ret = fread(&seed, sizeof(seed), 1, f);
> +        if (ret != 1)
> +            seed = time(NULL);
> +        fclose(f);
> +        srand(seed);
> +    } else
> +        srand(time(NULL));
> +}
> diff --git a/src/lxc/utils.h b/src/lxc/utils.h
> index 847a613..9018889 100644
> --- a/src/lxc/utils.h
> +++ b/src/lxc/utils.h
> @@ -265,5 +265,7 @@ extern void lxc_free_array(void **array, lxc_free_fn
> element_free_fn);
>  extern size_t lxc_array_len(void **array);
>  
>  extern void **lxc_append_null_to_array(void **array, size_t count);
> +//initialize rand with urandom
> +extern void randinit(void);
>  
>  #endif
> -- 
> 1.8.3.2
> 
> 
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