From a951e0b9efcbb64ca8b1d7c62c6c27a4498d21d6 Mon Sep 17 00:00:00 2001 From: Stefano Brivio Date: Wed, 18 May 2022 19:10:45 +0200 Subject: 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 --- util.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 52 insertions(+) (limited to 'util.c') diff --git a/util.c b/util.c index 9afd2a5..7ffd9d1 100644 --- a/util.c +++ b/util.c @@ -33,6 +33,8 @@ #include #include #include +#include +#include #include @@ -532,6 +534,56 @@ void drop_caps(void) } } +/** + * check_root() - Check if root in init ns, exit if we can't drop to user + */ +void check_root(struct ctx *c) +{ + 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); + + if (!c->uid) { + fprintf(stderr, "Don't run as root. Changing to nobody...\n"); +#ifndef GLIBC_NO_STATIC_NSS + pw = getpwnam("nobody"); + if (!pw) { + perror("getpwnam"); + exit(EXIT_FAILURE); + } + + c->uid = pw->pw_uid; + c->gid = pw->pw_gid; +#else + (void)pw; + + /* Common value for 'nobody', not really specified */ + c->uid = c->gid = 65534; +#endif + } + + if (!setgid(c->gid) && !setuid(c->uid)) + return; + + fprintf(stderr, "Can't change user/group, exiting"); + exit(EXIT_FAILURE); +} + /** * ns_enter() - Enter configured user (unless already joined) and network ns * @c: Execution context -- cgit v1.2.3