From patchwork Wed Jan 4 17:19:00 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Corey Bryant X-Patchwork-Id: 134303 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from lists.gnu.org (lists.gnu.org [140.186.70.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id 910601007D6 for ; Thu, 5 Jan 2012 04:19:42 +1100 (EST) Received: from localhost ([::1]:51646 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RiUV1-0007gx-MA for incoming@patchwork.ozlabs.org; Wed, 04 Jan 2012 12:19:39 -0500 Received: from eggs.gnu.org ([140.186.70.92]:55880) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RiUUo-0007KP-1r for qemu-devel@nongnu.org; Wed, 04 Jan 2012 12:19:32 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1RiUUm-0007EO-Fh for qemu-devel@nongnu.org; Wed, 04 Jan 2012 12:19:26 -0500 Received: from e39.co.us.ibm.com ([32.97.110.160]:40504) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RiUUm-0007EK-7j for qemu-devel@nongnu.org; Wed, 04 Jan 2012 12:19:24 -0500 Received: from /spool/local by e39.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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X-Received-From: 32.97.110.160 Cc: aliguori@us.ibm.com, rmarwah@linux.vnet.ibm.com Subject: [Qemu-devel] [PATCH v7 3/4] Add cap reduction support to enable use as SUID X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org The ideal way to use qemu-bridge-helper is to give it an fscap of using: setcap cap_net_admin=ep qemu-bridge-helper Unfortunately, most distros still do not have a mechanism to package files with fscaps applied. This means they'll have to SUID the qemu-bridge-helper binary. To improve security, use libcap to reduce our capability set to just cap_net_admin, then reduce privileges down to the calling user. This is hopefully close to equivalent to fscap support from a security perspective. Signed-off-by: Anthony Liguori Signed-off-by: Richa Marwaha Signed-off-by: Corey Bryant --- configure | 34 ++++++++++++++++++++++++++++++++++ qemu-bridge-helper.c | 36 ++++++++++++++++++++++++++++++++++++ 2 files changed, 70 insertions(+), 0 deletions(-) diff --git a/configure b/configure index 71774f4..3357fa6 100755 --- a/configure +++ b/configure @@ -133,6 +133,7 @@ vnc_thread="no" xen="" xen_ctrl_version="" linux_aio="" +cap="" attr="" libattr="" xfs="" @@ -668,6 +669,10 @@ for opt do ;; --enable-tcg-interpreter) tcg_interpreter="yes" ;; + --disable-cap) cap="no" + ;; + --enable-cap) cap="yes" + ;; --disable-spice) spice="no" ;; --enable-spice) spice="yes" @@ -1051,6 +1056,8 @@ echo " --disable-vde disable support for vde network" echo " --enable-vde enable support for vde network" echo " --disable-linux-aio disable Linux AIO support" echo " --enable-linux-aio enable Linux AIO support" +echo " --disable-cap disable libcap-ng support" +echo " --enable-cap enable libcap-ng support" echo " --disable-attr disables attr and xattr support" echo " --enable-attr enable attr and xattr support" echo " --disable-blobs disable installing provided firmware blobs" @@ -1735,6 +1742,29 @@ EOF fi ########################################## +# libcap-ng library probe +if test "$cap" != "no" ; then + cap_libs="-lcap-ng" + cat > $TMPC << EOF +#include +int main(void) +{ + capng_capability_to_name(CAPNG_EFFECTIVE); + return 0; +} +EOF + if compile_prog "" "$cap_libs" ; then + cap=yes + libs_tools="$cap_libs $libs_tools" + else + if test "$cap" = "yes" ; then + feature_not_found "cap" + fi + cap=no + fi +fi + +########################################## # Sound support libraries probe audio_drv_probe() @@ -2868,6 +2898,7 @@ echo "fdatasync $fdatasync" echo "madvise $madvise" echo "posix_madvise $posix_madvise" echo "uuid support $uuid" +echo "libcap-ng support $cap" echo "vhost-net support $vhost_net" echo "Trace backend $trace_backend" echo "Trace output file $trace_file-" @@ -2986,6 +3017,9 @@ fi if test "$vde" = "yes" ; then echo "CONFIG_VDE=y" >> $config_host_mak fi +if test "$cap" = "yes" ; then + echo "CONFIG_LIBCAP=y" >> $config_host_mak +fi for card in $audio_card_list; do def=CONFIG_`echo $card | tr '[:lower:]' '[:upper:]'` echo "$def=y" >> $config_host_mak diff --git a/qemu-bridge-helper.c b/qemu-bridge-helper.c index 01eeb38..aec5008 100644 --- a/qemu-bridge-helper.c +++ b/qemu-bridge-helper.c @@ -39,6 +39,10 @@ #include "net/tap-linux.h" +#ifdef CONFIG_LIBCAP +#include +#endif + #define DEFAULT_ACL_FILE CONFIG_QEMU_CONFDIR "/bridge.conf" enum { @@ -193,6 +197,27 @@ static int send_fd(int c, int fd) return sendmsg(c, &msg, 0); } +#ifdef CONFIG_LIBCAP +static int drop_privileges(void) +{ + /* clear all capabilities */ + capng_clear(CAPNG_SELECT_BOTH); + + if (capng_update(CAPNG_ADD, CAPNG_EFFECTIVE | CAPNG_PERMITTED, + CAP_NET_ADMIN) < 0) { + return -1; + } + + /* change to calling user's real uid and gid, retaining supplemental + * groups and CAP_NET_ADMIN */ + if (capng_change_id(getuid(), getgid(), CAPNG_CLEAR_BOUNDING)) { + return -1; + } + + return 0; +} +#endif + int main(int argc, char **argv) { struct ifreq ifr; @@ -207,6 +232,17 @@ int main(int argc, char **argv) int access_allowed, access_denied; int ret = EXIT_SUCCESS; +#ifdef CONFIG_LIBCAP + /* if we're run from an suid binary, immediately drop privileges preserving + * cap_net_admin */ + if (geteuid() == 0 && getuid() != geteuid()) { + if (drop_privileges() == -1) { + fprintf(stderr, "failed to drop privileges\n"); + return 1; + } + } +#endif + /* parse arguments */ for (index = 1; index < argc; index++) { if (strcmp(argv[index], "--use-vnet") == 0) {