capabilities: Add support for Linux capabilities(7)

This adds capabilities for start-stop-daemon by adding --capabilities
option. As a result, the user can specify the inheritable, ambient and
bounding set by define capabilities in the service script.

This fixes #314.

.github/workflows/ci-alpine-linux.yml

@@ -15,7 +15,9 @@ jobs:
             meson \
             pkgconf \
             linux-pam \
-            linux-pam-dev
+            linux-pam-dev \
+            libcap \
+            libcap-dev
       - name: checkout
         uses: actions/checkout@v2
       - run: meson setup builddir/

.github/workflows/ci-ubuntu.yml

@@ -9,7 +9,7 @@ jobs:
     steps:
     - uses: actions/checkout@v2
     - run: sudo apt-get update -q
-    - run: sudo apt-get install -q -y build-essential libpam-dev meson
+    - run: sudo apt-get install -q -y build-essential libpam-dev meson libcap-dev
     - run: meson setup builddir/
       env:
         CC: gcc
@@ -23,7 +23,7 @@ jobs:
     steps:
     - uses: actions/checkout@v2
     - run: sudo apt-get update -q
-    - run: sudo apt-get install -q -y build-essential clang libpam-dev meson
+    - run: sudo apt-get install -q -y build-essential clang libpam-dev meson libcap-dev
     - run: meson setup builddir/
       env:
         CC: clang

README.md

@@ -34,6 +34,7 @@ DESTDIR=/tmp/openrc-image
 MKBASHCOMP=no
 MKNET=no
 MKPAM=pam
+MKCAP=yes
 MKPREFIX=yes
 MKPKGCONFIG=no
 MKSELINUX=yes

man/start-stop-daemon.8

@@ -161,6 +161,9 @@ Cmd must be an absolute pathname, but relative to the path optionally given with
 .Fl r , -chroot .
 This process must be prepared to accept input on stdin and be able to
 log it or send it to another location.
+.It Fl -capabilities Ar cap-list
+Start the daemon with the listed inheritable, ambient and bounding capabilities.
+The format is the same as in cap_iab(3).
 .It Fl w , -wait Ar milliseconds
 Wait
 .Ar milliseconds

man/supervise-daemon.8

@@ -158,6 +158,9 @@ The logfile can also be a named pipe.
 The same thing as
 .Fl 1 , -stdout
 but with the standard error output.
+.It Fl -capabilities Ar cap-list
+Start the daemon with the listed inheritable, ambient and bounding capabilities.
+The format is the same as in cap_iab(3).
 .El
 .Sh ENVIRONMENT
 .Va SSD_IONICELEVEL

meson.build

@@ -57,6 +57,13 @@ if not pam_dep.found() and get_option('pam')
   error('Pam was requested but could not be located')
   endif
 
+cap_dep = dependency('libcap', version: '>=2.33', required : get_option('capabilities'))
+if cap_dep.found()
+  cc_cap_flags = '-DHAVE_CAP'
+else
+  cc_cap_flags = []
+endif
+
 option_pkg_prefix = get_option('pkg_prefix')
 if option_pkg_prefix == ''
   if os == 'Dragonfly' or os == 'FreeBSD'

meson_options.txt

@@ -14,6 +14,8 @@ option('os', type : 'combo',
   description : 'Operating System (autodetected if not specified)')
 option('pam', type : 'boolean',
   description : 'enable PAM support')
+option('capabilities', type : 'feature', value: 'auto',
+  description : 'enable capabilities support')
 option('pkg_prefix', type : 'string',
   description : 'default location where packages are installed')
 option('pkgconfig', type : 'boolean',

mk/os-Linux.mk

@@ -27,6 +27,12 @@ endif
 
 endif
 
+ifeq (${MKCAP},yes)
+CPPFLAGS+= -DHAVE_CAP
+LIBCAP?= -lcap
+LDADD += $(LIBCAP)
+endif
+
 ifeq (${MKAUDIT},yes)
 LIBAUDIT?=	-laudit
 CPPFLAGS+=	-DHAVE_AUDIT

service-script-guide.md

@@ -187,6 +187,21 @@ with
 
   * command_user="user:group"
 
+If your daemon should run with specific inheritable, ambient and
+bounding capabilities, then you can tell start-stop-daemon to launch
+it with
+
+  * capabilities="cap-list"
+
+The format is the same as in cap_iab(3). (Only on Linux)
+
+For example, to start the daemon with ambient and inheritable
+`cap_chown`, but without `cap_setpcap` in the bounding set, use
+the following value:
+```sh
+capabilities="^cap_chown,!cap_setpcap"
+```
+
 Finally, if your daemon always forks into the background but fails to
 create a PID file, then your only option is to use
 

sh/start-stop-daemon.sh

@@ -53,6 +53,7 @@ ssd_start()
 		${error_log+--stderr} $error_log \
 		${output_logger_arg} \
 		${error_logger_arg} \
+		${capabilities+--capabilities} "$capabilities" \
 		${procname:+--name} $procname \
 		${pidfile:+--pidfile} $pidfile \
 		${command_user+--user} $command_user \

sh/supervise-daemon.sh

@@ -36,6 +36,7 @@ supervise_start()
 		${respawn_period:+--respawn-period} $respawn_period \
 		${healthcheck_delay:+--healthcheck-delay} $healthcheck_delay \
 		${healthcheck_timer:+--healthcheck-timer} $healthcheck_timer \
+		${capabilities+--capabilities} "$capabilities" \
 		${command_user+--user} $command_user \
 		${umask+--umask} $umask \
 		${supervise_daemon_args:-${start_stop_daemon_args}} \

src/rc/meson.build

@@ -93,9 +93,9 @@ executable('runscript',
 executable('start-stop-daemon',
   ['start-stop-daemon.c', 'rc-pipes.c', rc_misc_c, rc_schedules_c,
 	rc_selinux_c, usage_c, version_h],
-  c_args : [cc_audit_flags, cc_branding_flags, cc_pam_flags, cc_selinux_flags],
+  c_args : [cc_audit_flags, cc_branding_flags, cc_pam_flags, cc_cap_flags, cc_selinux_flags],
   link_with: [libeinfo, librc],
-  dependencies: [audit_dep, dl_dep, pam_dep, pam_misc_dep, util_dep, selinux_dep, crypt_dep],
+  dependencies: [audit_dep, dl_dep, pam_dep, cap_dep, pam_misc_dep, util_dep, selinux_dep, crypt_dep],
   include_directories: [incdir, einfo_incdir, rc_incdir],
   install: true,
   install_dir: sbindir)
@@ -103,9 +103,9 @@ executable('start-stop-daemon',
 executable('supervise-daemon',
   ['supervise-daemon.c', rc_misc_c, rc_plugin_c, rc_schedules_c,
     usage_c, version_h],
-  c_args : [cc_branding_flags, cc_pam_flags, cc_selinux_flags],
+  c_args : [cc_branding_flags, cc_pam_flags, cc_cap_flags, cc_selinux_flags],
   link_with: [libeinfo, librc],
-  dependencies: [dl_dep, pam_dep, util_dep, selinux_dep],
+  dependencies: [dl_dep, pam_dep, cap_dep, util_dep, selinux_dep],
   include_directories: [incdir, einfo_incdir, rc_incdir],
   install: true,
   install_dir: sbindir)

src/rc/start-stop-daemon.c

@@ -55,6 +55,10 @@
 static struct pam_conv conv = { NULL, NULL};
 #endif
 
+#ifdef HAVE_CAP
+#include <sys/capability.h>
+#endif
+
 #include "einfo.h"
 #include "queue.h"
 #include "rc.h"
@@ -69,6 +73,7 @@ const char *extraopts = NULL;
 const char getoptstring[] = "I:KN:PR:Sa:bc:d:e:g:ik:mn:op:s:tu:r:w:x:1:2:3:4:" \
 	getoptstring_COMMON;
 const struct option longopts[] = {
+	{ "capabilities", 1, NULL, 0x100},
 	{ "ionice",       1, NULL, 'I'},
 	{ "stop",         0, NULL, 'K'},
 	{ "nicelevel",    1, NULL, 'N'},
@@ -101,6 +106,7 @@ const struct option longopts[] = {
 	longopts_COMMON
 };
 const char * const longopts_help[] = {
+	"Set the inheritable, ambient and bounding capabilities",
 	"Set an ionice class:data when starting",
 	"Stop daemon",
 	"Set a nicelevel when starting",
@@ -307,6 +313,9 @@ int main(int argc, char **argv)
 	mode_t numask = 022;
 	char **margv;
 	unsigned int start_wait = 0;
+#ifdef HAVE_CAP
+	cap_iab_t cap_iab = NULL;
+#endif
 
 	applet = basename_c(argv[0]);
 	atexit(cleanup);
@@ -353,6 +362,16 @@ int main(int argc, char **argv)
 	while ((opt = getopt_long(argc, argv, getoptstring, longopts,
 		    (int *) 0)) != -1)
 		switch (opt) {
+		case 0x100:
+#ifdef HAVE_CAP
+			cap_iab = cap_iab_from_text(optarg);
+			if (cap_iab == NULL)
+				eerrorx("Could not parse iab: %s", strerror(errno));
+#else
+			eerrorx("Capabilities support not enabled");
+#endif
+			break;
+
 		case 'I': /* --ionice */
 			if (sscanf(optarg, "%d:%d", &ionicec, &ioniced) == 0)
 				eerrorx("%s: invalid ionice `%s'",
@@ -850,13 +869,29 @@ int main(int argc, char **argv)
 		if (changeuser && initgroups(changeuser, gid))
 			eerrorx("%s: initgroups (%s, %d)",
 			    applet, changeuser, gid);
+#ifdef HAVE_CAP
+		if (uid && cap_setuid(uid))
+#else
 		if (uid && setuid(uid))
+#endif
 			eerrorx ("%s: unable to set userid to %d",
 			    applet, uid);
 
 		/* Close any fd's to the passwd database */
 		endpwent();
 
+#ifdef HAVE_CAP
+		if (cap_iab != NULL) {
+			i = cap_iab_set_proc(cap_iab);
+
+			if (cap_free(cap_iab) != 0)
+				eerrorx("Could not releasable memory: %s", strerror(errno));
+
+			if (i != 0)
+				eerrorx("Could not set iab: %s", strerror(errno));
+		}
+#endif
+
 #ifdef TIOCNOTTY
 		ioctl(tty_fd, TIOCNOTTY, 0);
 		close(tty_fd);

src/rc/supervise-daemon.c

@@ -57,6 +57,10 @@
 static struct pam_conv conv = { NULL, NULL};
 #endif
 
+#ifdef HAVE_CAP
+#include <sys/capability.h>
+#endif
+
 #include "einfo.h"
 #include "queue.h"
 #include "rc.h"
@@ -73,6 +77,7 @@ const char getoptstring[] = "A:a:D:d:e:g:H:I:Kk:m:N:p:R:r:s:Su:1:2:3" \
 const struct option longopts[] = {
 	{ "healthcheck-timer",        1, NULL, 'a'},
 	{ "healthcheck-delay",        1, NULL, 'A'},
+	{ "capabilities", 1, NULL, 0x100},
 	{ "respawn-delay",        1, NULL, 'D'},
 	{ "chdir",        1, NULL, 'd'},
 	{ "env",          1, NULL, 'e'},
@@ -98,6 +103,7 @@ const struct option longopts[] = {
 const char * const longopts_help[] = {
 	"set an initial health check delay",
 	"set a health check timer",
+	"Set the inheritable, ambient and bounding capabilities",
 	"Set a respawn delay",
 	"Change the PWD",
 	"Set an environment string",
@@ -152,6 +158,9 @@ static int fifo_fd = 0;
 static char *pidfile = NULL;
 static char *svcname = NULL;
 static bool verbose = false;
+#ifdef HAVE_CAP
+static cap_iab_t cap_iab = NULL;
+#endif
 
 extern char **environ;
 
@@ -398,12 +407,28 @@ static void child_process(char *exec, char **argv)
 		eerrorx("%s: unable to set groupid to %d", applet, gid);
 	if (changeuser && initgroups(changeuser, gid))
 		eerrorx("%s: initgroups (%s, %d)", applet, changeuser, gid);
+#ifdef HAVE_CAP
+	if (uid && cap_setuid(uid))
+#else
 	if (uid && setuid(uid))
+#endif
 		eerrorx ("%s: unable to set userid to %d", applet, uid);
 
 	/* Close any fd's to the passwd database */
 	endpwent();
 
+#ifdef HAVE_CAP
+	if (cap_iab != NULL) {
+		i = cap_iab_set_proc(cap_iab);
+
+		if (cap_free(cap_iab) != 0)
+			eerrorx("Could not releasable memory: %s", strerror(errno));
+
+		if (i != 0)
+			eerrorx("Could not set iab: %s", strerror(errno));
+	}
+#endif
+
 	/* remove the controlling tty */
 #ifdef TIOCNOTTY
 	ioctl(tty_fd, TIOCNOTTY, 0);
@@ -797,6 +822,16 @@ int main(int argc, char **argv)
 				eerrorx("%s: invalid health check delay %s", applet, optarg);
 			break;
 
+		case 0x100:
+#ifdef HAVE_CAP
+			cap_iab = cap_iab_from_text(optarg);
+			if (cap_iab == NULL)
+				eerrorx("Could not parse iab: %s", strerror(errno));
+#else
+			eerrorx("Capabilities support not enabled");
+#endif
+			break;
+
 		case 'D':  /* --respawn-delay time */
 			n = sscanf(optarg, "%d", &respawn_delay);
 			if (n	!= 1 || respawn_delay < 1)