mirror of
https://gitlab.com/libvirt/libvirt.git
synced 2024-08-05 08:23:48 +00:00
4feeb2d986
The virt-login-shell binary is a setuid program that takes no arguments. When invoked it looks at the invoking uid, resolves it to a username, and finds an LXC guest with the same name. It then starts the guest and runs the shell in side the namespaces of the container. Given this set of tasks the virt-login-shell binary needs to connect to libvirtd, make various other libvirt API calls. This is a problem for setuid binaries as various libraries that libvirt.so links to are not safe. For example, they have constructor functions which execute an unknown amount of code that can be influenced by env variables. For this reason virt-login-shell doesn't use libvirt.so, but instead links to a custom, cut down, set of source files sufficient to be a local client only. This introduces a problem for integrating glib2 into libvirt though, as once integrated, there would be no way to build virt-login-shell without an external dependancy on glib2 and this is definitely not setuid safe. To resolve this problem, we split the virt-login-shell binary into two parts. The first part is setuid and does almost nothing. It simply records the original uid+gid, and then invokes the virt-login-shell-helper binary. Crucially when it does this it completes scrubs all environment variables. It is thus safe for virt-login-shell-helper to link to the normal libvirt.so. Any things that constructor functions do cannot be influenced by user control env vars or cli args. Reviewed-by: Michal Privoznik <mprivozn@redhat.com> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
85 lines
2.4 KiB
C
85 lines
2.4 KiB
C
/*
|
|
* virt-login-shell.c: a setuid shell to connect to a container
|
|
*
|
|
* Copyright (C) 2019 Red Hat, Inc.
|
|
*
|
|
* This library is free software; you can redistribute it and/or
|
|
* modify it under the terms of the GNU Lesser General Public
|
|
* License as published by the Free Software Foundation; either
|
|
* version 2.1 of the License, or (at your option) any later version.
|
|
*
|
|
* This library is distributed in the hope that it will be useful,
|
|
* but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
|
|
* Lesser General Public License for more details.
|
|
*
|
|
* You should have received a copy of the GNU Lesser General Public
|
|
* License along with this library. If not, see
|
|
* <http://www.gnu.org/licenses/>.
|
|
*/
|
|
|
|
#include <config.h>
|
|
|
|
#include <unistd.h>
|
|
#include <sys/types.h>
|
|
#include <assert.h>
|
|
#include <stdio.h>
|
|
#include <stdlib.h>
|
|
#include <errno.h>
|
|
#include <string.h>
|
|
|
|
#include "configmake.h"
|
|
#include "intprops.h"
|
|
|
|
int main(int argc, char **argv) {
|
|
char uidstr[INT_BUFSIZE_BOUND(uid_t)];
|
|
char gidstr[INT_BUFSIZE_BOUND(gid_t)];
|
|
const char *const newargv[] = {
|
|
LIBEXECDIR "/virt-login-shell-helper",
|
|
uidstr,
|
|
gidstr,
|
|
NULL,
|
|
};
|
|
char *newenv[] = {
|
|
NULL,
|
|
NULL,
|
|
};
|
|
char *term = getenv("TERM");
|
|
|
|
if (getuid() == 0 || getgid() == 0) {
|
|
fprintf(stderr, "%s: must not be run as root\n", argv[0]);
|
|
exit(EXIT_FAILURE);
|
|
}
|
|
|
|
if (geteuid() != 0) {
|
|
fprintf(stderr, "%s: must be run as setuid root\n", argv[0]);
|
|
exit(EXIT_FAILURE);
|
|
}
|
|
|
|
if (argc != 1) {
|
|
fprintf(stderr, "%s: no arguments expected\n", argv[0]);
|
|
exit(EXIT_FAILURE);
|
|
}
|
|
|
|
if (term &&
|
|
asprintf(&(newenv[0]), "TERM=%s", term) < 0) {
|
|
fprintf(stderr, "%s: cannot set TERM env variable: %s\n",
|
|
argv[0], strerror(errno));
|
|
exit(EXIT_FAILURE);
|
|
}
|
|
|
|
assert(snprintf(uidstr, sizeof(uidstr), "%d", getuid()) < sizeof(uidstr));
|
|
assert(snprintf(gidstr, sizeof(gidstr), "%d", getgid()) < sizeof(gidstr));
|
|
|
|
if (setuid(0) < 0) {
|
|
fprintf(stderr, "%s: unable to set real UID to root: %s\n",
|
|
argv[0], strerror(errno));
|
|
exit(EXIT_FAILURE);
|
|
}
|
|
|
|
execve(newargv[0], (char *const*)newargv, newenv);
|
|
fprintf(stderr, "%s: failed to run %s/virt-login-shell-helper: %s\n",
|
|
argv[0], LIBEXECDIR, strerror(errno));
|
|
exit(EXIT_FAILURE);
|
|
}
|