shared/capability: go frugal on space for caps

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

diff --git a/src/shared/capability.c b/src/shared/capability.c
index b1be0438037f7c2efcd35aad3cd72944f18588b8..3f2f27e23fe4234c2660da30e5d99f76549aff14 100644 (file)
--- a/src/shared/capability.c
+++ b/src/shared/capability.c
@@ -230,8 +230,8 @@ int capability_bounding_set_drop_usermode(uint64_t drop) {
 }
 
 int drop_privileges(uid_t uid, gid_t gid, uint64_t keep_capabilities) {
-
         _cleanup_cap_free_ cap_t d = NULL;
+        unsigned i, j = 0;
         int r;
 
         /* Unfortunately we cannot leave privilege dropping to PID 1
@@ -247,6 +247,7 @@ int drop_privileges(uid_t uid, gid_t gid, uint64_t keep_capabilities) {
         if (setgroups(0, NULL) < 0)
                 return log_error_errno(errno, "Failed to drop auxiliary groups list: %m");
 
+        /* Ensure we keep the permitted caps across the setresuid() */
         if (prctl(PR_SET_KEEPCAPS, 1) < 0)
                 return log_error_errno(errno, "Failed to enable keep capabilities flag: %m");
 
@@ -257,31 +258,33 @@ int drop_privileges(uid_t uid, gid_t gid, uint64_t keep_capabilities) {
         if (prctl(PR_SET_KEEPCAPS, 0) < 0)
                 return log_error_errno(errno, "Failed to disable keep capabilities flag: %m");
 
+        /* Drop all caps from the bounding set, except the ones we want */
         r = capability_bounding_set_drop(~keep_capabilities, true);
         if (r < 0)
                 return log_error_errno(r, "Failed to drop capabilities: %m");
 
+        /* Now upgrade the permitted caps we still kept to effective caps */
         d = cap_init();
         if (!d)
                 return log_oom();
 
         if (keep_capabilities) {
-                cap_value_t bits[sizeof(keep_capabilities)*8];
-                unsigned i, j = 0;
+                cap_value_t bits[log2u64(keep_capabilities)];
 
-                for (i = 0; i < sizeof(keep_capabilities)*8; i++)
+                for (i = 0; i < ELEMENTSOF(bits); i++)
                         if (keep_capabilities & (1ULL << i))
                                 bits[j++] = i;
+                assert((keep_capabilities & (~1ULL << i)) == 0);
 
                 if (cap_set_flag(d, CAP_EFFECTIVE, j, bits, CAP_SET) < 0 ||
                     cap_set_flag(d, CAP_PERMITTED, j, bits, CAP_SET) < 0) {
                         log_error_errno(errno, "Failed to enable capabilities bits: %m");
                         return -errno;
                 }
-        }
 
-        if (cap_set_proc(d) < 0)
-                return log_error_errno(errno, "Failed to increase capabilities: %m");
+                if (cap_set_proc(d) < 0)
+                        return log_error_errno(errno, "Failed to increase capabilities: %m");
+        }
 
         return 0;
 }