ref: faa625a1d5ab47ac0438b2cea5b2bde1ea747b8b
dir: /sys/src/cmd/auth/as.c/
/* * as user cmd [arg...] - run cmd with args as user on this cpu server. * must be hostowner for this to work. * needs #¤/caphash and #¤/capuse. */ #include <u.h> #include <libc.h> #include <bio.h> #include <libsec.h> #include <auth.h> #include <authsrv.h> #include "authcmdlib.h" extern int newnsdebug; char *defargv[] = { "/bin/rc", "-i", nil }; char *namespace = nil; int becomeuser(char*); void usage(void) { fprint(2, "usage: %s [-d] [-n namespace] user [cmd [args...]]\n", argv0); exits("usage"); } void run(char **a) { exec(a[0], a); if(a[0][0] != '/' && a[0][0] != '#' && (a[0][0] != '.' || (a[0][1] != '/' && (a[0][1] != '.' || a[0][2] != '/')))) exec(smprint("/bin/%s", a[0]), a); sysfatal("exec: %s: %r", a[0]); } int mountfactotum(void) { int fd; /* get a link to factotum as new user */ fd = open("/srv/factotum", ORDWR); if(fd < 0) return -1; if(mount(fd, -1, "/mnt", MREPL, "") == -1){ close(fd); return -1; } return 0; } void main(int argc, char *argv[]) { ARGBEGIN{ case 'd': newnsdebug = 1; break; case 'n': namespace = EARGF(usage()); break; default: usage(); }ARGEND if(argc == 0) usage(); if(becomeuser(argv[0]) < 0) sysfatal("can't change uid for %s: %r", argv[0]); if(mountfactotum() < 0) sysfatal("can't mount factotum for uid for %s: %r", argv[0]); if(newns(argv[0], namespace) < 0) sysfatal("can't build namespace: %r"); argv++; if(--argc == 0) argv = defargv; run(argv); } /* * create a change uid capability */ char* mkcap(char *from, char *to) { uchar rand[20]; char *cap; char *key; int nfrom, nto; uchar hash[SHA1dlen]; int fd; fd = open("/dev/caphash", OCEXEC|OWRITE); if(fd < 0) return nil; /* create the capability */ nto = strlen(to); nfrom = strlen(from); cap = malloc(nfrom+1+nto+1+sizeof(rand)*3+1); if(cap == nil) sysfatal("malloc: %r"); sprint(cap, "%s@%s", from, to); genrandom(rand, sizeof(rand)); key = cap+nfrom+1+nto+1; enc64(key, sizeof(rand)*3, rand, sizeof(rand)); /* hash the capability */ hmac_sha1((uchar*)cap, strlen(cap), (uchar*)key, strlen(key), hash, nil); /* give the kernel the hash */ key[-1] = '@'; if(write(fd, hash, SHA1dlen) < 0){ close(fd); free(cap); return nil; } close(fd); return cap; } int usecap(char *cap) { int fd, rv; fd = open("/dev/capuse", OCEXEC|OWRITE); if(fd < 0) return -1; rv = write(fd, cap, strlen(cap)); close(fd); return rv; } int becomeuser(char *new) { char *cap; int rv; cap = mkcap(getuser(), new); if(cap == nil) return -1; rv = usecap(cap); free(cap); return rv; }