176 lines
2.7 KiB
C
176 lines
2.7 KiB
C
/*
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* as user cmd [arg...] - run cmd with args as user on this cpu server.
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* must be hostowner for this to work.
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* needs #¤/caphash and #¤/capuse.
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*/
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#include <u.h>
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#include <lib9.h>
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#include <bio.h>
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#include <libsec.h>
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#include <auth.h>
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#include <authsrv.h>
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#include "authcmdlib.h"
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int debug;
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int becomeuser(char*);
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void createuser(void);
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void *emalloc(uint32_t);
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void *erealloc(void*, uint32_t);
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void initcap(void);
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int mkcmd(char*, char*, int);
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int myauth(int, char*);
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int qidcmp(Qid, Qid);
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void runas(char *, char *);
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void usage(void);
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#pragma varargck argpos clog 1
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#pragma varargck argpos fatal 1
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static void
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fatal(char *fmt, ...)
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{
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char msg[256];
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va_list arg;
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va_start(arg, fmt);
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vseprint(msg, msg + sizeof msg, fmt, arg);
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va_end(arg);
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error("%s", msg);
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}
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void
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main(int argc, char *argv[])
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{
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debug = 0;
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ARGBEGIN{
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case 'd':
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debug = 1;
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break;
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default:
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usage();
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}ARGEND
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initcap();
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if(argc >= 2)
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runas(argv[0], argv[1]);
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else
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usage();
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}
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void
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runas(char *user, char *cmd)
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{
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if(becomeuser(user) < 0)
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sysfatal("can't change uid for %s: %r", user);
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putenv("service", "rx");
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execl("/bin/rc", "rc", "-lc", cmd, nil);
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sysfatal("exec /bin/rc: %r");
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}
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void *
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emalloc(uint32_t n)
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{
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void *p;
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if(p = mallocz(n, 1))
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return p;
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fatal("out of memory");
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return 0;
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}
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void *
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erealloc(void *p, uint32_t n)
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{
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if(p = realloc(p, n))
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return p;
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fatal("out of memory");
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return 0;
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}
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void
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usage(void)
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{
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fprint(2, "usage: %s [-c] [user] [command]\n", argv0);
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exits("usage");
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}
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/*
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* keep caphash fd open since opens of it could be disabled
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*/
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static int caphashfd;
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void
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initcap(void)
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{
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caphashfd = open("#¤/caphash", OCEXEC|OWRITE);
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if(caphashfd < 0)
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fprint(2, "%s: opening #¤/caphash: %r\n", argv0);
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}
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/*
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* create a change uid capability
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*/
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char*
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mkcap(char *from, char *to)
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{
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uint8_t rand[20];
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char *cap;
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char *key;
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int nfrom, nto;
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uint8_t hash[SHA1dlen];
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if(caphashfd < 0)
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return nil;
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/* create the capability */
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nto = strlen(to);
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nfrom = strlen(from);
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cap = emalloc(nfrom+1+nto+1+sizeof(rand)*3+1);
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sprint(cap, "%s@%s", from, to);
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genrandom(rand, sizeof(rand));
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key = cap+nfrom+1+nto+1;
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enc64(key, sizeof(rand)*3, rand, sizeof(rand));
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/* hash the capability */
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hmac_sha1((uint8_t*)cap, strlen(cap), (uint8_t*)key, strlen(key), hash, nil);
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/* give the kernel the hash */
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key[-1] = '@';
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if(write(caphashfd, hash, SHA1dlen) < 0){
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free(cap);
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return nil;
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}
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return cap;
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}
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int
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usecap(char *cap)
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{
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int fd, rv;
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fd = open("#¤/capuse", OWRITE);
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if(fd < 0)
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return -1;
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rv = write(fd, cap, strlen(cap));
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close(fd);
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return rv;
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}
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int
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becomeuser(char *new)
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{
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char *cap;
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int rv;
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cap = mkcap(getuser(), new);
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if(cap == nil)
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return -1;
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rv = usecap(cap);
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free(cap);
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newns(new, nil);
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return rv;
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}
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