Alternative to su/sudo on barebone system

If I understand correctly, you just need to su from root to some other user. Try copying an su binary (it won't need to be setuid root), but I don't know if that will work on Solaris. Or compile a small C program that drops privileges and executes a command.

Here's a small “down-only” su. Minimally tested. Should compile as is under Solaris and *BSD; you need to -D_BDS_SOURCE and #include <grp.h> under Linux, and other platforms may require commenting out the call to the common but non-standard setgroups. Run as e.g. sugexec UID GID bash /path/to/script (you must pass numerical user and group IDs, to avoid depending on any form of user database that may not be available in the chroot).

#include <errno.h> #include <stdlib.h> #include <stdio.h> #include <string.h> #include <sys/types.h> #include <unistd.h> void die(char *argv0, char *obj, char *msg) { if (msg == NULL) msg = strerror(errno); fprintf(stderr, "%s: %s: %s\n", argv0, obj, msg); exit(127); } int main(int argc, char *argv[]) { uid_t uid; gid_t gid; char *endp; /* Command line parsing */ if (argc <= 3) { fprintf(stderr, "Usage: %s UID GID COMMAND [ARG...]\n", argv[0]==NULL ? "sugexec" : argv[0]); exit(127); } uid = strtoul(argv[1], &endp, 0); if (*endp) die(argv[0], argv[1], "Bad uid"); gid = strtoul(argv[2], &endp, 0); if (*endp) die(argv[0], argv[2], "Bad gid"); /* Drop to specified user and group */ if (setgid(gid)) die(argv[0], "setgid", NULL); if (setgroups(0, NULL)) die(argv[0], "setgroups", NULL); if (setuid(uid)) die(argv[0], "setuid", NULL); /* Execute the command */ execvp(argv[3], argv + 3); die(argv[0], argv[3], NULL); }