capability: use /proc/sys/kernel/cap_last_cap

[elogind.git] / src / shared / capability.c

diff --git a/src/shared/capability.c b/src/shared/capability.c
index 5d156ab3cd62e95f44f2347b309ca6ad3daf566e..b1be0438037f7c2efcd35aad3cd72944f18588b8 100644 (file)
--- a/src/shared/capability.c
+++ b/src/shared/capability.c
@@ -54,11 +54,25 @@ int have_effective_cap(int value) {
 unsigned long cap_last_cap(void) {
         static thread_local unsigned long saved;
         static thread_local bool valid = false;
+        _cleanup_free_ char *content = NULL;
         unsigned long p;
+        int r;
 
         if (valid)
                 return saved;
 
+        /* available since linux-3.2 */
+        r = read_one_line_file("/proc/sys/kernel/cap_last_cap", &content);
+        if (r >= 0) {
+                r = safe_atolu(content, &p);
+                if (r >= 0) {
+                        saved = p;
+                        valid = true;
+                        return p;
+                }
+        }
+
+        /* fall back to syscall-probing for pre linux-3.2 */
         p = (unsigned long) CAP_LAST_CAP;
 
         if (prctl(PR_CAPBSET_READ, p) < 0) {
@@ -271,3 +285,21 @@ int drop_privileges(uid_t uid, gid_t gid, uint64_t keep_capabilities) {
 
         return 0;
 }
+
+int drop_capability(cap_value_t cv) {
+        _cleanup_cap_free_ cap_t tmp_cap = NULL;
+
+        tmp_cap = cap_get_proc();
+        if (!tmp_cap)
+                return -errno;
+
+        if ((cap_set_flag(tmp_cap, CAP_INHERITABLE, 1, &cv, CAP_CLEAR) < 0) ||
+            (cap_set_flag(tmp_cap, CAP_PERMITTED, 1, &cv, CAP_CLEAR) < 0) ||
+            (cap_set_flag(tmp_cap, CAP_EFFECTIVE, 1, &cv, CAP_CLEAR) < 0))
+                return -errno;
+
+        if (cap_set_proc(tmp_cap) < 0)
+                return -errno;
+
+        return 0;
+}