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/*
* 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"
int debug;
int becomeuser(char*);
void createuser(void);
void *emalloc(ulong);
void *erealloc(void*, ulong);
void initcap(void);
int mkcmd(char*, char*, int);
int myauth(int, char*);
int qidcmp(Qid, Qid);
void runas(char *, char *);
void usage(void);
#pragma varargck argpos clog 1
#pragma varargck argpos fatal 1
static void
fatal(char *fmt, ...)
{
char msg[256];
va_list arg;
va_start(arg, fmt);
vseprint(msg, msg + sizeof msg, fmt, arg);
va_end(arg);
error("%s", msg);
}
void
main(int argc, char *argv[])
{
debug = 0;
ARGBEGIN{
case 'd':
debug = 1;
break;
default:
usage();
}ARGEND
initcap();
if(argc >= 2)
runas(argv[0], argv[1]);
else
usage();
}
void
runas(char *user, char *cmd)
{
if(becomeuser(user) < 0)
sysfatal("can't change uid for %s: %r", user);
putenv("service", "rx");
execl("/bin/rc", "rc", "-lc", cmd, nil);
sysfatal("exec /bin/rc: %r");
}
void *
emalloc(ulong n)
{
void *p;
if(p = mallocz(n, 1))
return p;
fatal("out of memory");
return 0;
}
void *
erealloc(void *p, ulong n)
{
if(p = realloc(p, n))
return p;
fatal("out of memory");
return 0;
}
void
usage(void)
{
fprint(2, "usage: %s [-c] [user] [command]\n", argv0);
exits("usage");
}
/*
* keep caphash fd open since opens of it could be disabled
*/
static int caphashfd;
void
initcap(void)
{
caphashfd = open("#¤/caphash", OCEXEC|OWRITE);
if(caphashfd < 0)
fprint(2, "%s: opening #¤/caphash: %r\n", argv0);
}
/*
* create a change uid capability
*/
char*
mkcap(char *from, char *to)
{
uchar rand[20];
char *cap;
char *key;
int nfrom, nto;
uchar hash[SHA1dlen];
if(caphashfd < 0)
return nil;
/* create the capability */
nto = strlen(to);
nfrom = strlen(from);
cap = emalloc(nfrom+1+nto+1+sizeof(rand)*3+1);
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(caphashfd, hash, SHA1dlen) < 0){
free(cap);
return nil;
}
return cap;
}
int
usecap(char *cap)
{
int fd, rv;
fd = open("#¤/capuse", 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);
newns(new, nil);
return rv;
}
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