Split checking for root from dropping root privilege

check_root() both checks to see if we are root (in the init namespace),
and if we are drops to an unprivileged user.  To make future cleanups
simpler, split the checking for root (now in check_root()) from the actual
dropping of privilege (now in drop_root()).

Note that this does slightly alter semantics.  Previously we would only
setuid() if we were originally root (in the init namespace).  Now we will
always setuid() and setgid(), though it won't actually change anything if
we weren't privileged to begin with.  This also means that we will now
always attempt to switch to the user specified with --runas, even if we
aren't (init namespace) root to begin with.  Obviously this will fail with
an error if we weren't privileged to start with.  --help and the man page
are updated accordingly.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

1 files changed, 3 insertions, 2 deletions

diff --git a/conf.c b/conf.c
index 0fe5266..545f61d 100644
--- a/conf.c
+++ b/conf.c
@@ -747,8 +747,8 @@ static void usage(const char *name)
 	info(   "    default: run in background if started from a TTY");
 	info(   "  -e, --stderr		Log to stderr too");
 	info(   "    default: log to system logger only if started from a TTY");
-	info(   "  --runas UID|UID:GID 	Use given UID, GID if started as root");
-	info(   "    UID and GID can be numeric, or login and group names");
+	info(   "  --runas UID|UID:GID 	Run as given UID, GID, which can be");
+	info(   "    numeric, or login and group names");
 	info(   "    default: drop to user \"nobody\"");
 	info(   "  -h, --help		Display this help message and exit");
 
@@ -1500,6 +1500,7 @@ void conf(struct ctx *c, int argc, char **argv)
 	} while (name != -1);
 
 	check_root(&uid, &gid);
+	drop_root(uid, gid);
 
 	if (c->mode == MODE_PASTA) {
 		if (*netns && optind != argc) {