conf: Add --runas option, changing to given UID and GID if started as root

On some systems, user and group "nobody" might not be available. The
new --runas option allows to override the default "nobody" choice if
started as root.

Now that we allow this, drop the initgroups() call that was used to
add any additional groups for the given user, as that might now
grant unnecessarily broad permissions. For instance, several
distributions have a "kvm" group to allow regular user access to
/dev/kvm, and we don't need that in passt or pasta.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

1 files changed, 0 insertions, 46 deletions

diff --git a/passt.c b/passt.c
index e5064f8..dd0229a 100644
--- a/passt.c
+++ b/passt.c
@@ -46,8 +46,6 @@
 #include <sys/stat.h>
 #include <sys/prctl.h>
 #include <stddef.h>
-#include <pwd.h>
-#include <grp.h>
 #include <netinet/udp.h>
 #include <netinet/tcp.h>
 #include <netinet/if_ether.h>
@@ -191,49 +189,6 @@ static void seccomp(const struct ctx *c)
 }
 
 /**
- * check_root() - Warn if root in init, exit if we can't drop to nobody
- */
-static void check_root(void)
-{
-	const char root_uid_map[] = "         0          0 4294967295";
-	struct passwd *pw;
-	char buf[BUFSIZ];
-	int fd;
-
-	if (getuid() && geteuid())
-		return;
-
-	if ((fd = open("/proc/self/uid_map", O_RDONLY | O_CLOEXEC)) < 0)
-		return;
-
-	if (read(fd, buf, BUFSIZ) != sizeof(root_uid_map) ||
-	    strncmp(buf, root_uid_map, sizeof(root_uid_map) - 1)) {
-		close(fd);
-		return;
-	}
-
-	close(fd);
-
-	fprintf(stderr, "Don't run this as root. Changing to nobody...\n");
-#ifndef GLIBC_NO_STATIC_NSS
-	pw = getpwnam("nobody");
-	if (!pw) {
-		perror("getpwnam");
-		exit(EXIT_FAILURE);
-	}
-
-	if (!initgroups(pw->pw_name, pw->pw_gid) &&
-	    !setgid(pw->pw_gid) && !setuid(pw->pw_uid))
-		return;
-#else
-	(void)pw;
-#endif
-
-	fprintf(stderr, "Can't change to user/group nobody, exiting");
-	exit(EXIT_FAILURE);
-}
-
-/**
  * sandbox() - Unshare IPC, mount, PID, UTS, and user namespaces, "unmount" root
  *
  * Return: negative error code on failure, zero on success
@@ -336,7 +291,6 @@ int main(int argc, char **argv)
 
 	arch_avx2_exec(argv);
 
-	check_root();
 	drop_caps();
 
 	c.pasta_userns_fd = c.pasta_netns_fd = c.fd_tap = c.fd_tap_listen = -1;