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xemu/softmmu/qemu-seccomp.c
Daniel P. Berrangé 4638057110 seccomp: block setns, unshare and execveat syscalls 
setns/unshare are used to change namespaces which is not something QEMU
needs to be able todo.

execveat is a new variant of execve so should be blocked just like
execve already is.

Acked-by: Eduardo Otubo <otubo@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
2022-02-16 18:52:40 +00:00

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/*
* QEMU seccomp mode 2 support with libseccomp
*
* Copyright IBM, Corp. 2012
*
* Authors:
* Eduardo Otubo <eotubo@br.ibm.com>
*
* This work is licensed under the terms of the GNU GPL, version 2. See
* the COPYING file in the top-level directory.
*
* Contributions after 2012-01-13 are licensed under the terms of the
* GNU GPL, version 2 or (at your option) any later version.
*/
#include "qemu/osdep.h"
#include "qapi/error.h"
#include "qemu/config-file.h"
#include "qemu/option.h"
#include "qemu/module.h"
#include <sys/prctl.h>
#include <seccomp.h>
#include "sysemu/seccomp.h"
#include <linux/seccomp.h>
/* For some architectures (notably ARM) cacheflush is not supported until
* libseccomp 2.2.3, but configure enforces that we are using a more recent
* version on those hosts, so it is OK for this check to be less strict.
*/
#if SCMP_VER_MAJOR >= 3
#define HAVE_CACHEFLUSH
#elif SCMP_VER_MAJOR == 2 && SCMP_VER_MINOR >= 2
#define HAVE_CACHEFLUSH
#endif
struct QemuSeccompSyscall {
int32_t num;
uint8_t set;
uint8_t narg;
const struct scmp_arg_cmp *arg_cmp;
uint32_t action;
};
const struct scmp_arg_cmp sched_setscheduler_arg[] = {
/* was SCMP_A1(SCMP_CMP_NE, SCHED_IDLE), but expanded due to GCC 4.x bug */
{ .arg = 1, .op = SCMP_CMP_NE, .datum_a = SCHED_IDLE }
};
/*
* See 'NOTES' in 'man 2 clone' - s390 & cross have 'flags' in
* different position to other architectures
*/
#if defined(HOST_S390X) || defined(HOST_S390) || defined(HOST_CRIS)
#define CLONE_FLAGS_ARG 1
#else
#define CLONE_FLAGS_ARG 0
#endif
#ifndef CLONE_PIDFD
# define CLONE_PIDFD 0x00001000
#endif
#define REQUIRE_CLONE_FLAG(flag) \
const struct scmp_arg_cmp clone_arg ## flag[] = { \
{ .arg = CLONE_FLAGS_ARG, \
.op = SCMP_CMP_MASKED_EQ, \
.datum_a = flag, .datum_b = 0 } }
#define FORBID_CLONE_FLAG(flag) \
const struct scmp_arg_cmp clone_arg ## flag[] = { \
{ .arg = CLONE_FLAGS_ARG, \
.op = SCMP_CMP_MASKED_EQ, \
.datum_a = flag, .datum_b = flag } }
#define RULE_CLONE_FLAG(flag) \
{ SCMP_SYS(clone), QEMU_SECCOMP_SET_SPAWN, \
ARRAY_SIZE(clone_arg ## flag), clone_arg ## flag, SCMP_ACT_TRAP }
/* If no CLONE_* flags are set, except CSIGNAL, deny */
const struct scmp_arg_cmp clone_arg_none[] = {
{ .arg = CLONE_FLAGS_ARG,
.op = SCMP_CMP_MASKED_EQ,
.datum_a = ~(CSIGNAL), .datum_b = 0 }
};
/*
* pthread_create should always set all of these.
*/
REQUIRE_CLONE_FLAG(CLONE_VM);
REQUIRE_CLONE_FLAG(CLONE_FS);
REQUIRE_CLONE_FLAG(CLONE_FILES);
REQUIRE_CLONE_FLAG(CLONE_SIGHAND);
REQUIRE_CLONE_FLAG(CLONE_THREAD);
REQUIRE_CLONE_FLAG(CLONE_SYSVSEM);
REQUIRE_CLONE_FLAG(CLONE_SETTLS);
REQUIRE_CLONE_FLAG(CLONE_PARENT_SETTID);
REQUIRE_CLONE_FLAG(CLONE_CHILD_CLEARTID);
/*
* Musl sets this in pthread_create too, but it is
* obsolete and harmless since its behaviour is
* subsumed under CLONE_THREAD
*/
/*REQUIRE_CLONE_FLAG(CLONE_DETACHED);*/
/*
* These all indicate an attempt to spawn a process
* instead of a thread, or other undesirable scenarios
*/
FORBID_CLONE_FLAG(CLONE_PIDFD);
FORBID_CLONE_FLAG(CLONE_PTRACE);
FORBID_CLONE_FLAG(CLONE_VFORK);
FORBID_CLONE_FLAG(CLONE_PARENT);
FORBID_CLONE_FLAG(CLONE_NEWNS);
FORBID_CLONE_FLAG(CLONE_UNTRACED);
FORBID_CLONE_FLAG(CLONE_NEWCGROUP);
FORBID_CLONE_FLAG(CLONE_NEWUTS);
FORBID_CLONE_FLAG(CLONE_NEWIPC);
FORBID_CLONE_FLAG(CLONE_NEWUSER);
FORBID_CLONE_FLAG(CLONE_NEWPID);
FORBID_CLONE_FLAG(CLONE_NEWNET);
FORBID_CLONE_FLAG(CLONE_IO);
static const struct QemuSeccompSyscall denylist[] = {
/* default set of syscalls that should get blocked */
{ SCMP_SYS(reboot), QEMU_SECCOMP_SET_DEFAULT,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(swapon), QEMU_SECCOMP_SET_DEFAULT,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(swapoff), QEMU_SECCOMP_SET_DEFAULT,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(syslog), QEMU_SECCOMP_SET_DEFAULT,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(mount), QEMU_SECCOMP_SET_DEFAULT,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(umount), QEMU_SECCOMP_SET_DEFAULT,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(kexec_load), QEMU_SECCOMP_SET_DEFAULT,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(afs_syscall), QEMU_SECCOMP_SET_DEFAULT,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(break), QEMU_SECCOMP_SET_DEFAULT,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(ftime), QEMU_SECCOMP_SET_DEFAULT,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(getpmsg), QEMU_SECCOMP_SET_DEFAULT,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(gtty), QEMU_SECCOMP_SET_DEFAULT,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(lock), QEMU_SECCOMP_SET_DEFAULT,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(mpx), QEMU_SECCOMP_SET_DEFAULT,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(prof), QEMU_SECCOMP_SET_DEFAULT,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(profil), QEMU_SECCOMP_SET_DEFAULT,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(putpmsg), QEMU_SECCOMP_SET_DEFAULT,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(security), QEMU_SECCOMP_SET_DEFAULT,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(stty), QEMU_SECCOMP_SET_DEFAULT,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(tuxcall), QEMU_SECCOMP_SET_DEFAULT,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(ulimit), QEMU_SECCOMP_SET_DEFAULT,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(vserver), QEMU_SECCOMP_SET_DEFAULT,
0, NULL, SCMP_ACT_TRAP },
/* obsolete */
{ SCMP_SYS(readdir), QEMU_SECCOMP_SET_OBSOLETE,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(_sysctl), QEMU_SECCOMP_SET_OBSOLETE,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(bdflush), QEMU_SECCOMP_SET_OBSOLETE,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(create_module), QEMU_SECCOMP_SET_OBSOLETE,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(get_kernel_syms), QEMU_SECCOMP_SET_OBSOLETE,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(query_module), QEMU_SECCOMP_SET_OBSOLETE,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(sgetmask), QEMU_SECCOMP_SET_OBSOLETE,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(ssetmask), QEMU_SECCOMP_SET_OBSOLETE,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(sysfs), QEMU_SECCOMP_SET_OBSOLETE,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(uselib), QEMU_SECCOMP_SET_OBSOLETE,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(ustat), QEMU_SECCOMP_SET_OBSOLETE,
0, NULL, SCMP_ACT_TRAP },
/* privileged */
{ SCMP_SYS(setuid), QEMU_SECCOMP_SET_PRIVILEGED,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(setgid), QEMU_SECCOMP_SET_PRIVILEGED,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(setpgid), QEMU_SECCOMP_SET_PRIVILEGED,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(setsid), QEMU_SECCOMP_SET_PRIVILEGED,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(setreuid), QEMU_SECCOMP_SET_PRIVILEGED,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(setregid), QEMU_SECCOMP_SET_PRIVILEGED,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(setresuid), QEMU_SECCOMP_SET_PRIVILEGED,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(setresgid), QEMU_SECCOMP_SET_PRIVILEGED,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(setfsuid), QEMU_SECCOMP_SET_PRIVILEGED,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(setfsgid), QEMU_SECCOMP_SET_PRIVILEGED,
0, NULL, SCMP_ACT_TRAP },
/* spawn */
{ SCMP_SYS(fork), QEMU_SECCOMP_SET_SPAWN,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(vfork), QEMU_SECCOMP_SET_SPAWN,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(execve), QEMU_SECCOMP_SET_SPAWN,
0, NULL, SCMP_ACT_TRAP },
{ SCMP_SYS(clone), QEMU_SECCOMP_SET_SPAWN,
ARRAY_SIZE(clone_arg_none), clone_arg_none, SCMP_ACT_TRAP },
RULE_CLONE_FLAG(CLONE_VM),
RULE_CLONE_FLAG(CLONE_FS),
RULE_CLONE_FLAG(CLONE_FILES),
RULE_CLONE_FLAG(CLONE_SIGHAND),
RULE_CLONE_FLAG(CLONE_THREAD),
RULE_CLONE_FLAG(CLONE_SYSVSEM),
RULE_CLONE_FLAG(CLONE_SETTLS),
RULE_CLONE_FLAG(CLONE_PARENT_SETTID),
RULE_CLONE_FLAG(CLONE_CHILD_CLEARTID),
/*RULE_CLONE_FLAG(CLONE_DETACHED),*/
RULE_CLONE_FLAG(CLONE_PIDFD),
RULE_CLONE_FLAG(CLONE_PTRACE),
RULE_CLONE_FLAG(CLONE_VFORK),
RULE_CLONE_FLAG(CLONE_PARENT),
RULE_CLONE_FLAG(CLONE_NEWNS),
RULE_CLONE_FLAG(CLONE_UNTRACED),
RULE_CLONE_FLAG(CLONE_NEWCGROUP),
RULE_CLONE_FLAG(CLONE_NEWUTS),
RULE_CLONE_FLAG(CLONE_NEWIPC),
RULE_CLONE_FLAG(CLONE_NEWUSER),
RULE_CLONE_FLAG(CLONE_NEWPID),
RULE_CLONE_FLAG(CLONE_NEWNET),
RULE_CLONE_FLAG(CLONE_IO),
#ifdef __SNR_clone3
{ SCMP_SYS(clone3), QEMU_SECCOMP_SET_SPAWN,
0, NULL, SCMP_ACT_ERRNO(ENOSYS) },
#endif
#ifdef __SNR_execveat
{ SCMP_SYS(execveat), QEMU_SECCOMP_SET_SPAWN },
#endif
{ SCMP_SYS(setns), QEMU_SECCOMP_SET_SPAWN },
{ SCMP_SYS(unshare), QEMU_SECCOMP_SET_SPAWN },
/* resource control */
{ SCMP_SYS(setpriority), QEMU_SECCOMP_SET_RESOURCECTL,
0, NULL, SCMP_ACT_ERRNO(EPERM) },
{ SCMP_SYS(sched_setparam), QEMU_SECCOMP_SET_RESOURCECTL,
0, NULL, SCMP_ACT_ERRNO(EPERM) },
{ SCMP_SYS(sched_setscheduler), QEMU_SECCOMP_SET_RESOURCECTL,
ARRAY_SIZE(sched_setscheduler_arg), sched_setscheduler_arg,
SCMP_ACT_ERRNO(EPERM) },
{ SCMP_SYS(sched_setaffinity), QEMU_SECCOMP_SET_RESOURCECTL,
0, NULL, SCMP_ACT_ERRNO(EPERM) },
};
static inline __attribute__((unused)) int
qemu_seccomp(unsigned int operation, unsigned int flags, void *args)
{
#ifdef __NR_seccomp
return syscall(__NR_seccomp, operation, flags, args);
#else
errno = ENOSYS;
return -1;
#endif
}
static uint32_t qemu_seccomp_update_action(uint32_t action)
{
#if defined(SECCOMP_GET_ACTION_AVAIL) && defined(SCMP_ACT_KILL_PROCESS) && \
defined(SECCOMP_RET_KILL_PROCESS)
if (action == SCMP_ACT_TRAP) {
static int kill_process = -1;
if (kill_process == -1) {
uint32_t action = SECCOMP_RET_KILL_PROCESS;
if (qemu_seccomp(SECCOMP_GET_ACTION_AVAIL, 0, &action) == 0) {
kill_process = 1;
} else {
kill_process = 0;
}
}
if (kill_process == 1) {
return SCMP_ACT_KILL_PROCESS;
}
}
#endif
return action;
}
static int seccomp_start(uint32_t seccomp_opts, Error **errp)
{
int rc = -1;
unsigned int i = 0;
scmp_filter_ctx ctx;
ctx = seccomp_init(SCMP_ACT_ALLOW);
if (ctx == NULL) {
error_setg(errp, "failed to initialize seccomp context");
goto seccomp_return;
}
rc = seccomp_attr_set(ctx, SCMP_FLTATR_CTL_TSYNC, 1);
if (rc != 0) {
error_setg_errno(errp, -rc,
"failed to set seccomp thread synchronization");
goto seccomp_return;
}
for (i = 0; i < ARRAY_SIZE(denylist); i++) {
uint32_t action;
if (!(seccomp_opts & denylist[i].set)) {
continue;
}
action = qemu_seccomp_update_action(denylist[i].action);
rc = seccomp_rule_add_array(ctx, action, denylist[i].num,
denylist[i].narg, denylist[i].arg_cmp);
if (rc < 0) {
error_setg_errno(errp, -rc,
"failed to add seccomp denylist rules");
goto seccomp_return;
}
}
rc = seccomp_load(ctx);
if (rc < 0) {
error_setg_errno(errp, -rc,
"failed to load seccomp syscall filter in kernel");
}
seccomp_return:
seccomp_release(ctx);
return rc < 0 ? -1 : 0;
}
int parse_sandbox(void *opaque, QemuOpts *opts, Error **errp)
{
if (qemu_opt_get_bool(opts, "enable", false)) {
uint32_t seccomp_opts = QEMU_SECCOMP_SET_DEFAULT
| QEMU_SECCOMP_SET_OBSOLETE;
const char *value = NULL;
value = qemu_opt_get(opts, "obsolete");
if (value) {
if (g_str_equal(value, "allow")) {
seccomp_opts &= ~QEMU_SECCOMP_SET_OBSOLETE;
} else if (g_str_equal(value, "deny")) {
/* this is the default option, this if is here
* to provide a little bit of consistency for
* the command line */
} else {
error_setg(errp, "invalid argument for obsolete");
return -1;
}
}
value = qemu_opt_get(opts, "elevateprivileges");
if (value) {
if (g_str_equal(value, "deny")) {
seccomp_opts |= QEMU_SECCOMP_SET_PRIVILEGED;
} else if (g_str_equal(value, "children")) {
seccomp_opts |= QEMU_SECCOMP_SET_PRIVILEGED;
/* calling prctl directly because we're
* not sure if host has CAP_SYS_ADMIN set*/
if (prctl(PR_SET_NO_NEW_PRIVS, 1)) {
error_setg(errp, "failed to set no_new_privs aborting");
return -1;
}
} else if (g_str_equal(value, "allow")) {
/* default value */
} else {
error_setg(errp, "invalid argument for elevateprivileges");
return -1;
}
}
value = qemu_opt_get(opts, "spawn");
if (value) {
if (g_str_equal(value, "deny")) {
seccomp_opts |= QEMU_SECCOMP_SET_SPAWN;
} else if (g_str_equal(value, "allow")) {
/* default value */
} else {
error_setg(errp, "invalid argument for spawn");
return -1;
}
}
value = qemu_opt_get(opts, "resourcecontrol");
if (value) {
if (g_str_equal(value, "deny")) {
seccomp_opts |= QEMU_SECCOMP_SET_RESOURCECTL;
} else if (g_str_equal(value, "allow")) {
/* default value */
} else {
error_setg(errp, "invalid argument for resourcecontrol");
return -1;
}
}
if (seccomp_start(seccomp_opts, errp) < 0) {
return -1;
}
}
return 0;
}
static QemuOptsList qemu_sandbox_opts = {
.name = "sandbox",
.implied_opt_name = "enable",
.head = QTAILQ_HEAD_INITIALIZER(qemu_sandbox_opts.head),
.desc = {
{
.name = "enable",
.type = QEMU_OPT_BOOL,
},
{
.name = "obsolete",
.type = QEMU_OPT_STRING,
},
{
.name = "elevateprivileges",
.type = QEMU_OPT_STRING,
},
{
.name = "spawn",
.type = QEMU_OPT_STRING,
},
{
.name = "resourcecontrol",
.type = QEMU_OPT_STRING,
},
{ /* end of list */ }
},
};
static void seccomp_register(void)
{
bool add = false;
/* FIXME: use seccomp_api_get() >= 2 check when released */
#if defined(SECCOMP_FILTER_FLAG_TSYNC)
int check;
/* check host TSYNC capability, it returns errno == ENOSYS if unavailable */
check = qemu_seccomp(SECCOMP_SET_MODE_FILTER,
SECCOMP_FILTER_FLAG_TSYNC, NULL);
if (check < 0 && errno == EFAULT) {
add = true;
}
#endif
if (add) {
qemu_add_opts(&qemu_sandbox_opts);
}
}
opts_init(seccomp_register);
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