From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:39508) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RHGhm-0003zH-NE for qemu-devel@nongnu.org; Fri, 21 Oct 2011 11:08:21 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1RHGhg-00069y-7s for qemu-devel@nongnu.org; Fri, 21 Oct 2011 11:08:18 -0400 Received: from e36.co.us.ibm.com ([32.97.110.154]:52931) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RHGhf-00069m-OX for qemu-devel@nongnu.org; Fri, 21 Oct 2011 11:08:12 -0400 Received: from /spool/local by e36.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 21 Oct 2011 09:07:55 -0600 Received: from d03av03.boulder.ibm.com (d03av03.boulder.ibm.com [9.17.195.169]) by d03relay05.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id p9LF7YrK085592 for ; Fri, 21 Oct 2011 09:07:36 -0600 Received: from d03av03.boulder.ibm.com (loopback [127.0.0.1]) by d03av03.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id p9LF7TRc013954 for ; Fri, 21 Oct 2011 09:07:31 -0600 From: Corey Bryant Date: Fri, 21 Oct 2011 11:07:22 -0400 Message-Id: <1319209643-3866-4-git-send-email-coreyb@linux.vnet.ibm.com> In-Reply-To: <1319209643-3866-1-git-send-email-coreyb@linux.vnet.ibm.com> References: <1319209643-3866-1-git-send-email-coreyb@linux.vnet.ibm.com> Subject: [Qemu-devel] [PATCH v2 3/4] Add cap reduction support to enable use as SUID List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: aliguori@us.ibm.com, rmarwah@linux.vnet.ibm.com 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 | 39 +++++++++++++++++++++++++++++++++++++++ 2 files changed, 73 insertions(+), 0 deletions(-) diff --git a/configure b/configure index 6c8b659..fed66b0 100755 --- a/configure +++ b/configure @@ -128,6 +128,7 @@ vnc_thread="no" xen="" xen_ctrl_version="" linux_aio="" +cap="" attr="" xfs="" @@ -653,6 +654,10 @@ for opt do ;; --enable-kvm) kvm="yes" ;; + --disable-cap) cap="no" + ;; + --enable-cap) cap="yes" + ;; --disable-spice) spice="no" ;; --enable-spice) spice="yes" @@ -1032,6 +1037,8 @@ 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" @@ -1638,6 +1645,29 @@ 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() @@ -2735,6 +2765,7 @@ 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 $trace_file-" @@ -2846,6 +2877,9 @@ fi if test "$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 db257d5..b1562eb 100644 --- a/qemu-bridge-helper.c +++ b/qemu-bridge-helper.c @@ -33,6 +33,10 @@ #include "net/tap-linux.h" +#ifdef CONFIG_LIBCAP +#include +#endif + #define MAX_ACLS (128) #define DEFAULT_ACL_FILE CONFIG_QEMU_CONFDIR "/bridge.conf" @@ -185,6 +189,27 @@ 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; @@ -198,6 +223,20 @@ int main(int argc, char **argv) int acl_count = 0; int i, access_allowed, access_denied; + /* if we're run from an suid binary, immediately drop privileges preserving + * cap_net_admin -- exit immediately if libcap not configured */ + if (geteuid() == 0 && getuid() != geteuid()) { +#ifdef CONFIG_LIBCAP + if (drop_privileges() == -1) { + fprintf(stderr, "failed to drop privileges\n"); + return 1; + } +#else + fprintf(stderr, "failed to drop privileges\n"); + return 1; +#endif + } + /* parse arguments */ if (argc < 3 || argc > 4) { fprintf(stderr, "Usage: %s [--use-vnet] BRIDGE FD\n", argv[0]); -- 1.7.3.4