4 files changed, 50 insertions, 23 deletions
diff --git a/src/basic/capability-util.c b/src/basic/capability-util.c
index f8db6e0212..c3de20a0e8 100644
--- a/src/basic/capability-util.c
+++ b/src/basic/capability-util.c
@@ -296,8 +296,9 @@ int drop_privileges(uid_t uid, gid_t gid, uint64_t keep_capabilities) {
         if (setresgid(gid, gid, gid) < 0)
                 return log_error_errno(errno, "Failed to change group ID: %m");
 
-        if (maybe_setgroups(0, NULL) < 0)
-                return log_error_errno(errno, "Failed to drop auxiliary groups list: %m");
+        r = maybe_setgroups(0, NULL);
+        if (r < 0)
+                return log_error_errno(r, "Failed to drop auxiliary groups list: %m");
 
         /* Ensure we keep the permitted caps across the setresuid() */
         if (prctl(PR_SET_KEEPCAPS, 1) < 0)
diff --git a/src/basic/socket-util.c b/src/basic/socket-util.c
index 5c829e0e7e..1662c04705 100644
--- a/src/basic/socket-util.c
+++ b/src/basic/socket-util.c
@@ -1060,3 +1060,20 @@ struct cmsghdr* cmsg_find(struct msghdr *mh, int level, int type, socklen_t leng
 
         return NULL;
 }
+
+int socket_ioctl_fd(void) {
+        int fd;
+
+        /* Create a socket to invoke the various network interface ioctl()s on. Traditionally only AF_INET was good for
+         * that. Since kernel 4.6 AF_NETLINK works for this too. We first try to use AF_INET hence, but if that's not
+         * available (for example, because it is made unavailable via SECCOMP or such), we'll fall back to the more
+         * generic AF_NETLINK. */
+
+        fd = socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC, 0);
+        if (fd < 0)
+                fd = socket(AF_NETLINK, SOCK_RAW|SOCK_CLOEXEC, NETLINK_GENERIC);
+        if (fd < 0)
+                return -errno;
+
+        return fd;
+}
diff --git a/src/basic/socket-util.h b/src/basic/socket-util.h
index 2536b085f9..2ef572badb 100644
--- a/src/basic/socket-util.h
+++ b/src/basic/socket-util.h
@@ -154,3 +154,5 @@ struct cmsghdr* cmsg_find(struct msghdr *mh, int level, int type, socklen_t leng
                          1 + strnlen(_sa->sun_path+1, sizeof(_sa->sun_path)-1) : \
                          strnlen(_sa->sun_path, sizeof(_sa->sun_path))); \
         })
+
+int socket_ioctl_fd(void);
diff --git a/src/basic/user-util.c b/src/basic/user-util.c
index 16496fccfa..de6c93056e 100644
--- a/src/basic/user-util.c
+++ b/src/basic/user-util.c
@@ -460,9 +460,11 @@ int get_shell(char **_s) {
 }
 
 int reset_uid_gid(void) {
+        int r;
 
-        if (maybe_setgroups(0, NULL) < 0)
-                return -errno;
+        r = maybe_setgroups(0, NULL);
+        if (r < 0)
+                return r;
 
         if (setresgid(0, 0, 0) < 0)
                 return -errno;
@@ -605,25 +607,30 @@ bool valid_home(const char *p) {
 }
 
 int maybe_setgroups(size_t size, const gid_t *list) {
-        static int cached_can_setgroups = -1;
-        /* check if setgroups is allowed before we try to drop all the auxiliary groups */
-        if (size == 0) {
-                if (cached_can_setgroups < 0) {
-                        _cleanup_free_ char *setgroups_content = NULL;
-                        int r = read_one_line_file("/proc/self/setgroups", &setgroups_content);
-                        if (r < 0 && errno != ENOENT)
-                                return r;
-                        if (r < 0) {
-                                /* old kernels don't have /proc/self/setgroups, so assume we can use setgroups */
-                                cached_can_setgroups = true;
-                        } else {
-                                cached_can_setgroups = streq(setgroups_content, "allow");
-                                if (!cached_can_setgroups)
-                                        log_debug("skip setgroups, /proc/self/setgroups is set to 'deny'");
-                        }
-                }
-                if (!cached_can_setgroups)
+        int r;
+
+        /* Check if setgroups is allowed before we try to drop all the auxiliary groups */
+        if (size == 0) { /* Dropping all aux groups? */
+                _cleanup_free_ char *setgroups_content = NULL;
+                bool can_setgroups;
+
+                r = read_one_line_file("/proc/self/setgroups", &setgroups_content);
+                if (r == -ENOENT)
+                        /* Old kernels don't have /proc/self/setgroups, so assume we can use setgroups */
+                        can_setgroups = true;
+                else if (r < 0)
+                        return r;
+                else
+                        can_setgroups = streq(setgroups_content, "allow");
+
+                if (!can_setgroups) {
+                        log_debug("Skipping setgroups(), /proc/self/setgroups is set to 'deny'");
                         return 0;
+                }
         }
-        return setgroups(size, list);
+
+        if (setgroups(size, list) < 0)
+                return -errno;
+
+        return 0;
 }