[lxc-devel] [PATCH] hash lxcname for use in monitor unix socket sun_path[108]

[Serge Hallyn]

Quoting Dwight Engen (dwight.engen at oracle.com):
> - Also convert to unix abstract socket
> - A simple FNV hash is used instead of SHA-1 since we may not HAVE_GNUTLS
> 
> Signed-off-by: Dwight Engen <dwight.engen at oracle.com>

Acked-by: Serge E. Hallyn <serge.hallyn at ubuntu.com>

Thanks Dwight!  Works great.

> ---
>  src/lxc/monitor.c | 60 ++++++++++++++++++++++++++++++++++++-------------------
>  1 file changed, 40 insertions(+), 20 deletions(-)
> 
> diff --git a/src/lxc/monitor.c b/src/lxc/monitor.c
> index bdcc581..64e9987 100644
> --- a/src/lxc/monitor.c
> +++ b/src/lxc/monitor.c
> @@ -28,6 +28,8 @@
>  #include <string.h>
>  #include <stdlib.h>
>  #include <fcntl.h>
> +#include <inttypes.h>
> +#include <stdint.h>
>  #include <sys/types.h>
>  #include <sys/stat.h>
>  #include <sys/param.h>
> @@ -123,38 +125,56 @@ int lxc_monitor_close(int fd)
>  	return close(fd);
>  }
>  
> +/* Note we don't use SHA-1 here as we don't want to depend on HAVE_GNUTLS.
> + * FNV has good anti collision properties and we're not worried
> + * about pre-image resistance or one-way-ness, we're just trying to make
> + * the name unique in the 108 bytes of space we have.
> + */
> +#define FNV1A_64_INIT ((uint64_t)0xcbf29ce484222325ULL)
> +static uint64_t fnv_64a_buf(void *buf, size_t len, uint64_t hval)
> +{
> +	unsigned char *bp;
> +
> +	for(bp = buf; bp < (unsigned char *)buf + len; bp++)
> +	{
> +		/* xor the bottom with the current octet */
> +		hval ^= (uint64_t)*bp;
> +
> +		/* gcc optimised:
> +		 * multiply by the 64 bit FNV magic prime mod 2^64
> +		 */
> +		hval += (hval << 1) + (hval << 4) + (hval << 5) +
> +			(hval << 7) + (hval << 8) + (hval << 40);
> +	}
> +
> +	return hval;
> +}
> +
>  int lxc_monitor_sock_name(const char *lxcpath, struct sockaddr_un *addr) {
>  	size_t len;
>  	int ret;
> -	char *sockname = &addr->sun_path[0]; // 1 for abstract
> -	const char *rundir;
> +	char *sockname = &addr->sun_path[1];
> +	char path[PATH_MAX+18];
> +	uint64_t hash;
>  
> -	/* addr.sun_path is only 108 bytes.
> -	 * should we take a hash of lxcpath? a subset of it? ftok()? we need
> -	 * to make sure it is unique.
> +	/* addr.sun_path is only 108 bytes, so we hash the full name and
> +	 * then append as much of the name as we can fit.
>  	 */
>  	memset(addr, 0, sizeof(*addr));
>  	addr->sun_family = AF_UNIX;
>  	len = sizeof(addr->sun_path) - 1;
> -	rundir = get_rundir();
> -	ret = snprintf(sockname, len, "%s/lxc/%s", rundir, lxcpath);
> -	if (ret < 0 || ret >= len) {
> -		ERROR("rundir/lxcpath (%s/%s) too long for monitor unix socket", rundir, lxcpath);
> +	ret = snprintf(path, sizeof(path), "lxc/%s/monitor-sock", lxcpath);
> +	if (ret < 0 || ret >= sizeof(path)) {
> +		ERROR("lxcpath %s too long for monitor unix socket", lxcpath);
>  		return -1;
>  	}
> -	process_lock();
> -	ret = mkdir_p(sockname, 0755);
> -	process_unlock();
> -	if (ret < 0) {
> -		ERROR("unable to create monitor sock %s", sockname);
> -		return ret;
> -	}
>  
> -	ret = snprintf(sockname, len, "%s/lxc/%s/monitor-sock", rundir, lxcpath);
> -	if (ret < 0 || ret >= len) {
> -		ERROR("rundir/lxcpath (%s/%s) too long for monitor unix socket", rundir, lxcpath);
> +	hash = fnv_64a_buf(path, ret, FNV1A_64_INIT);
> +	ret = snprintf(sockname, len, "lxc/%016" PRIx64 "/%s", hash, lxcpath);
> +	if (ret < 0)
>  		return -1;
> -	}
> +	sockname[sizeof(addr->sun_path)-2] = '\0';
> +	INFO("using monitor sock name %s", sockname);
>  	return 0;
>  }
>  
> -- 
> 1.8.1.4
>