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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"
extern int newnsdebug;
char *defargv[] = { "/bin/rc", "-i", nil };
char *namespace = nil;
int becomeuser(char*);
void initcap(void);
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]);
}
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();
initcap();
if(becomeuser(argv[0]) < 0)
sysfatal("can't change 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);
}
/*
* 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", 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 = 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(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);
return rv;
}
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