capabilities: when dropping capabilities system-wide also drop them from usermode helpers

This hooks things up with /proc/sys/kernel/usermodehelper/bset and
/proc/sys/kernel/usermodehelper/inheritable.

TODO

@@ -6,9 +6,9 @@ Fedora 18:
 * chrony/ntp target?
 
 Bugfixes:
-* fix building of --disable-logind, hournald and coredunp pull-in parts of sd_login
+* log_warning() in journald gets looped back into journal via kmsg?
 
-* fix emergency mode breakage after the Type=idle change
+* fix building of --disable-logind, hournald and coredunp pull-in parts of sd_login
 
 * remove MS_SHARED from src/core/execute.c and src/test/test-ns.c. They are always combined
   with MS_REMOUNT, which currently does nothing in the kernel, but might which fail in the
@@ -31,7 +31,9 @@ Bugfixes:
 * properly handle .mount unit state tracking when two mount points are stacked one on top of another on the exact same mount point.
 
 Features:
-* logind: listen to power/suspend/lid-button events
+* parse kernel cmdline option for capability bset
+
+* logind: listen to power-button events
   - run poweroff if no session is active
   - console session should beep when we refuse to poweroff
   - graphical sessions will show a dialog, like they do already today
@@ -39,8 +41,6 @@ Features:
 
 * journalctl /dev/sda, journalctl /usr/bin/httpd, journalctl --device=b12:8 (--device=n12, --device=+usb:1-1)
 
-* also reset /proc/sys/kernel/usermodehelper/bset /proc/sys/kernel/usermodehelper/inheritable in system.conf's CapabilityBoundingSet=
-
 * make use of /sys/power/wake_lock in inhibitors
 
 * introduce "systemctl help" which invokes man for the man pages listed in Documentation=
@@ -49,7 +49,7 @@ Features:
 
 * make sure show-logs checks for utf8 validity, not ascii validity
 
-* add CapbilityBoundingSet to system.conf to set system-wide caps bounds, and same for TimerSlackNS
+* add TimerSlackNS to system.conf to set system-wide caps bounds
 
 * when breaking cycles drop sysv services first, then services from /run, then from /etc, then from /usr
 

src/core/main.c

@@ -1493,6 +1493,11 @@ int main(int argc, char *argv[]) {
                         log_error("Failed to drop capability bounding set: %s", strerror(-r));
                         goto finish;
                 }
+                r = capability_bounding_set_drop_usermode(arg_capability_bounding_set_drop);
+                if (r < 0) {
+                        log_error("Failed to drop capability bounding set of usermode helpers: %s", strerror(-r));
+                        goto finish;
+                }
         }
 
         r = manager_new(arg_running_as, &m);

src/shared/capability.c

@@ -171,3 +171,54 @@ finish:
 
         return r;
 }
+
+static int drop_from_file(const char *fn, uint64_t drop) {
+        int r, k;
+        uint32_t hi, lo;
+        uint64_t current, after;
+        char *p;
+
+        r = read_one_line_file(fn, &p);
+        if (r < 0)
+                return r;
+
+        assert_cc(sizeof(hi) == sizeof(unsigned));
+        assert_cc(sizeof(lo) == sizeof(unsigned));
+
+        k = sscanf(p, "%u %u", &lo, &hi);
+        free(p);
+
+        if (k != 2)
+                return -EIO;
+
+        current = (uint64_t) lo | ((uint64_t) hi << 32ULL);
+        after = current & ~drop;
+
+        if (current == after)
+                return 0;
+
+        lo = (unsigned) (after & 0xFFFFFFFFULL);
+        hi = (unsigned) ((after >> 32ULL) & 0xFFFFFFFFULL);
+
+        if (asprintf(&p, "%u %u", lo, hi) < 0)
+                return -ENOMEM;
+
+        r = write_one_line_file(fn, p);
+        free(p);
+
+        return r;
+}
+
+int capability_bounding_set_drop_usermode(uint64_t drop) {
+        int r;
+
+        r = drop_from_file("/proc/sys/kernel/usermodehelper/inheritable", drop);
+        if (r < 0)
+                return r;
+
+        r = drop_from_file("/proc/sys/kernel/usermodehelper/bset", drop);
+        if (r < 0)
+                return r;
+
+        return r;
+}

src/shared/capability.h

@@ -27,6 +27,7 @@
 
 unsigned long cap_last_cap(void);
 int have_effective_cap(int value);
-int capability_bounding_set_drop(uint64_t caps, bool right_now);
+int capability_bounding_set_drop(uint64_t drop, bool right_now);
+int capability_bounding_set_drop_usermode(uint64_t drop);
 
 #endif