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.

3 files changed, 58 insertions, 1 deletions

diff --git a/src/core/main.c b/src/core/main.c
index 9248c388a4..4c3ee7d5a2 100644
--- a/src/core/main.c
+++ b/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);
diff --git a/src/shared/capability.c b/src/shared/capability.c
index 08b7a209da..9b743e86d0 100644
--- a/src/shared/capability.c
+++ b/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;
+}
diff --git a/src/shared/capability.h b/src/shared/capability.h
index 0cc5dd08aa..6cb31bb510 100644
--- a/src/shared/capability.h
+++ b/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