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os-posix: Provide new -runas <uid>:<gid> facility 

This allows the caller to specify a uid and gid to use, even if there
is no corresponding password entry.  This will be useful in certain
Xen configurations.

We don't support just -runas <uid> because: (i) deprivileging without
calling setgroups would be ineffective (ii) given only a uid we don't
know what gid we ought to use (since uids may eppear in multiple
passwd file entries with different gids).

Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>
CC: Paolo Bonzini <pbonzini@redhat.com>
CC: Markus Armbruster <armbru@redhat.com>
CC: Daniel P. Berrange <berrange@redhat.com>
CC: Michael Tokarev <mjt@tls.msk.ru>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
This commit is contained in:
Ian Jackson 2017-09-15 18:10:44 +01:00 committed by Ian Jackson
parent f0a2171bf9
commit 2c42f1e801
2 changed files with 67 additions and 13 deletions
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77
os-posix.c
View File

@ -41,7 +41,14 @@
#include <sys/prctl.h>
#endif
static struct passwd *user_pwd;
/*
* Must set all three of these at once.
* Legal combinations are unset by name by uid
*/
static struct passwd *user_pwd; /* NULL non-NULL NULL */
static uid_t user_uid = (uid_t)-1; /* -1 -1 >=0 */
static gid_t user_gid = (gid_t)-1; /* -1 -1 >=0 */
static const char *chroot_dir;
static int daemonize;
static int daemon_pipe;
@ -127,6 +134,33 @@ void os_set_proc_name(const char *s)
#endif
}
static bool os_parse_runas_uid_gid(const char *optarg)
{
unsigned long lv;
const char *ep;
uid_t got_uid;
gid_t got_gid;
int rc;
rc = qemu_strtoul(optarg, &ep, 0, &lv);
got_uid = lv; /* overflow here is ID in C99 */
if (rc || *ep != ':' || got_uid != lv || got_uid == (uid_t)-1) {
return false;
}
rc = qemu_strtoul(ep + 1, 0, 0, &lv);
got_gid = lv; /* overflow here is ID in C99 */
if (rc || got_gid != lv || got_gid == (gid_t)-1) {
return false;
}
user_pwd = NULL;
user_uid = got_uid;
user_gid = got_gid;
return true;
}
/*
* Parse OS specific command line options.
* return 0 if option handled, -1 otherwise
@ -144,8 +178,13 @@ void os_parse_cmd_args(int index, const char *optarg)
#endif
case QEMU_OPTION_runas:
user_pwd = getpwnam(optarg);
if (!user_pwd) {
fprintf(stderr, "User \"%s\" doesn't exist\n", optarg);
if (user_pwd) {
user_uid = -1;
user_gid = -1;
} else if (!os_parse_runas_uid_gid(optarg)) {
error_report("User \"%s\" doesn't exist"
" (and is not <uid>:<gid>)",
optarg);
exit(1);
}
break;
@ -165,18 +204,32 @@ void os_parse_cmd_args(int index, const char *optarg)
static void change_process_uid(void)
{
if (user_pwd) {
if (setgid(user_pwd->pw_gid) < 0) {
error_report("Failed to setgid(%d)", user_pwd->pw_gid);
assert((user_uid == (uid_t)-1) || user_pwd == NULL);
assert((user_uid == (uid_t)-1) ==
(user_gid == (gid_t)-1));
if (user_pwd || user_uid != (uid_t)-1) {
gid_t intended_gid = user_pwd ? user_pwd->pw_gid : user_gid;
uid_t intended_uid = user_pwd ? user_pwd->pw_uid : user_uid;
if (setgid(intended_gid) < 0) {
error_report("Failed to setgid(%d)", intended_gid);
exit(1);
}
if (initgroups(user_pwd->pw_name, user_pwd->pw_gid) < 0) {
error_report("Failed to initgroups(\"%s\", %d)",
user_pwd->pw_name, user_pwd->pw_gid);
exit(1);
if (user_pwd) {
if (initgroups(user_pwd->pw_name, user_pwd->pw_gid) < 0) {
error_report("Failed to initgroups(\"%s\", %d)",
user_pwd->pw_name, user_pwd->pw_gid);
exit(1);
}
} else {
if (setgroups(1, &user_gid) < 0) {
error_report("Failed to setgroups(1, [%d])",
user_gid);
exit(1);
}
}
if (setuid(user_pwd->pw_uid) < 0) {
error_report("Failed to setuid(%d)", user_pwd->pw_uid);
if (setuid(intended_uid) < 0) {
error_report("Failed to setuid(%d)", intended_uid);
exit(1);
}
if (setuid(0) != -1) {

3
qemu-options.hx
View File

@ -3765,7 +3765,8 @@ ETEXI
#ifndef _WIN32
DEF("runas", HAS_ARG, QEMU_OPTION_runas, \
"-runas user change to user id user just before starting the VM\n",
"-runas user change to user id user just before starting the VM\n" \
" user can be numeric uid:gid instead\n",
QEMU_ARCH_ALL)
#endif
STEXI