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2ce949a4c1
Recent GLibC calls sched_getaffinity in code paths related to malloc and when QEMU blocks access, it sends it off into a bad codepath resulting in stack exhaustion[1]. The GLibC bug is being fixed[2], but none the less, GLibC has valid reasons to want to use sched_getaffinity. It is not unreasonable for code to want to run many resource syscalls for information gathering, so it is a bit too harsh for QEMU to block them. [1] https://bugzilla.redhat.com/show_bug.cgi?id=1975693 [2] https://sourceware.org/pipermail/libc-alpha/2021-June/128271.html Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com> Acked-by: Eduardo Otubo <otubo@redhat.com> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
324 lines
11 KiB
C
324 lines
11 KiB
C
/*
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* QEMU seccomp mode 2 support with libseccomp
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*
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* Copyright IBM, Corp. 2012
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*
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* Authors:
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* Eduardo Otubo <eotubo@br.ibm.com>
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*
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* This work is licensed under the terms of the GNU GPL, version 2. See
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* the COPYING file in the top-level directory.
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*
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* Contributions after 2012-01-13 are licensed under the terms of the
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* GNU GPL, version 2 or (at your option) any later version.
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*/
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#include "qemu/osdep.h"
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#include "qapi/error.h"
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#include "qemu/config-file.h"
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#include "qemu/option.h"
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#include "qemu/module.h"
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#include <sys/prctl.h>
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#include <seccomp.h>
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#include "sysemu/seccomp.h"
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#include <linux/seccomp.h>
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/* For some architectures (notably ARM) cacheflush is not supported until
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* libseccomp 2.2.3, but configure enforces that we are using a more recent
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* version on those hosts, so it is OK for this check to be less strict.
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*/
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#if SCMP_VER_MAJOR >= 3
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#define HAVE_CACHEFLUSH
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#elif SCMP_VER_MAJOR == 2 && SCMP_VER_MINOR >= 2
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#define HAVE_CACHEFLUSH
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#endif
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struct QemuSeccompSyscall {
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int32_t num;
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uint8_t set;
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uint8_t narg;
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const struct scmp_arg_cmp *arg_cmp;
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};
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const struct scmp_arg_cmp sched_setscheduler_arg[] = {
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/* was SCMP_A1(SCMP_CMP_NE, SCHED_IDLE), but expanded due to GCC 4.x bug */
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{ .arg = 1, .op = SCMP_CMP_NE, .datum_a = SCHED_IDLE }
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};
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static const struct QemuSeccompSyscall denylist[] = {
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/* default set of syscalls that should get blocked */
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{ SCMP_SYS(reboot), QEMU_SECCOMP_SET_DEFAULT },
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{ SCMP_SYS(swapon), QEMU_SECCOMP_SET_DEFAULT },
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{ SCMP_SYS(swapoff), QEMU_SECCOMP_SET_DEFAULT },
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{ SCMP_SYS(syslog), QEMU_SECCOMP_SET_DEFAULT },
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{ SCMP_SYS(mount), QEMU_SECCOMP_SET_DEFAULT },
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{ SCMP_SYS(umount), QEMU_SECCOMP_SET_DEFAULT },
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{ SCMP_SYS(kexec_load), QEMU_SECCOMP_SET_DEFAULT },
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{ SCMP_SYS(afs_syscall), QEMU_SECCOMP_SET_DEFAULT },
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{ SCMP_SYS(break), QEMU_SECCOMP_SET_DEFAULT },
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{ SCMP_SYS(ftime), QEMU_SECCOMP_SET_DEFAULT },
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{ SCMP_SYS(getpmsg), QEMU_SECCOMP_SET_DEFAULT },
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{ SCMP_SYS(gtty), QEMU_SECCOMP_SET_DEFAULT },
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{ SCMP_SYS(lock), QEMU_SECCOMP_SET_DEFAULT },
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{ SCMP_SYS(mpx), QEMU_SECCOMP_SET_DEFAULT },
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{ SCMP_SYS(prof), QEMU_SECCOMP_SET_DEFAULT },
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{ SCMP_SYS(profil), QEMU_SECCOMP_SET_DEFAULT },
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{ SCMP_SYS(putpmsg), QEMU_SECCOMP_SET_DEFAULT },
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{ SCMP_SYS(security), QEMU_SECCOMP_SET_DEFAULT },
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{ SCMP_SYS(stty), QEMU_SECCOMP_SET_DEFAULT },
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{ SCMP_SYS(tuxcall), QEMU_SECCOMP_SET_DEFAULT },
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{ SCMP_SYS(ulimit), QEMU_SECCOMP_SET_DEFAULT },
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{ SCMP_SYS(vserver), QEMU_SECCOMP_SET_DEFAULT },
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/* obsolete */
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{ SCMP_SYS(readdir), QEMU_SECCOMP_SET_OBSOLETE },
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{ SCMP_SYS(_sysctl), QEMU_SECCOMP_SET_OBSOLETE },
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{ SCMP_SYS(bdflush), QEMU_SECCOMP_SET_OBSOLETE },
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{ SCMP_SYS(create_module), QEMU_SECCOMP_SET_OBSOLETE },
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{ SCMP_SYS(get_kernel_syms), QEMU_SECCOMP_SET_OBSOLETE },
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{ SCMP_SYS(query_module), QEMU_SECCOMP_SET_OBSOLETE },
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{ SCMP_SYS(sgetmask), QEMU_SECCOMP_SET_OBSOLETE },
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{ SCMP_SYS(ssetmask), QEMU_SECCOMP_SET_OBSOLETE },
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{ SCMP_SYS(sysfs), QEMU_SECCOMP_SET_OBSOLETE },
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{ SCMP_SYS(uselib), QEMU_SECCOMP_SET_OBSOLETE },
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{ SCMP_SYS(ustat), QEMU_SECCOMP_SET_OBSOLETE },
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/* privileged */
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{ SCMP_SYS(setuid), QEMU_SECCOMP_SET_PRIVILEGED },
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{ SCMP_SYS(setgid), QEMU_SECCOMP_SET_PRIVILEGED },
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{ SCMP_SYS(setpgid), QEMU_SECCOMP_SET_PRIVILEGED },
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{ SCMP_SYS(setsid), QEMU_SECCOMP_SET_PRIVILEGED },
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{ SCMP_SYS(setreuid), QEMU_SECCOMP_SET_PRIVILEGED },
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{ SCMP_SYS(setregid), QEMU_SECCOMP_SET_PRIVILEGED },
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{ SCMP_SYS(setresuid), QEMU_SECCOMP_SET_PRIVILEGED },
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{ SCMP_SYS(setresgid), QEMU_SECCOMP_SET_PRIVILEGED },
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{ SCMP_SYS(setfsuid), QEMU_SECCOMP_SET_PRIVILEGED },
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{ SCMP_SYS(setfsgid), QEMU_SECCOMP_SET_PRIVILEGED },
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/* spawn */
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{ SCMP_SYS(fork), QEMU_SECCOMP_SET_SPAWN },
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{ SCMP_SYS(vfork), QEMU_SECCOMP_SET_SPAWN },
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{ SCMP_SYS(execve), QEMU_SECCOMP_SET_SPAWN },
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/* resource control */
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{ SCMP_SYS(setpriority), QEMU_SECCOMP_SET_RESOURCECTL },
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{ SCMP_SYS(sched_setparam), QEMU_SECCOMP_SET_RESOURCECTL },
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{ SCMP_SYS(sched_setscheduler), QEMU_SECCOMP_SET_RESOURCECTL,
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ARRAY_SIZE(sched_setscheduler_arg), sched_setscheduler_arg },
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{ SCMP_SYS(sched_setaffinity), QEMU_SECCOMP_SET_RESOURCECTL },
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};
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static inline __attribute__((unused)) int
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qemu_seccomp(unsigned int operation, unsigned int flags, void *args)
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{
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#ifdef __NR_seccomp
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return syscall(__NR_seccomp, operation, flags, args);
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#else
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errno = ENOSYS;
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return -1;
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#endif
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}
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static uint32_t qemu_seccomp_get_action(int set)
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{
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switch (set) {
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case QEMU_SECCOMP_SET_DEFAULT:
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case QEMU_SECCOMP_SET_OBSOLETE:
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case QEMU_SECCOMP_SET_PRIVILEGED:
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case QEMU_SECCOMP_SET_SPAWN: {
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#if defined(SECCOMP_GET_ACTION_AVAIL) && defined(SCMP_ACT_KILL_PROCESS) && \
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defined(SECCOMP_RET_KILL_PROCESS)
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static int kill_process = -1;
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if (kill_process == -1) {
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uint32_t action = SECCOMP_RET_KILL_PROCESS;
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if (qemu_seccomp(SECCOMP_GET_ACTION_AVAIL, 0, &action) == 0) {
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kill_process = 1;
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} else {
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kill_process = 0;
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}
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}
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if (kill_process == 1) {
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return SCMP_ACT_KILL_PROCESS;
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}
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#endif
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return SCMP_ACT_TRAP;
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}
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case QEMU_SECCOMP_SET_RESOURCECTL:
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return SCMP_ACT_ERRNO(EPERM);
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default:
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g_assert_not_reached();
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}
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}
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static int seccomp_start(uint32_t seccomp_opts, Error **errp)
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{
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int rc = -1;
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unsigned int i = 0;
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scmp_filter_ctx ctx;
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ctx = seccomp_init(SCMP_ACT_ALLOW);
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if (ctx == NULL) {
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error_setg(errp, "failed to initialize seccomp context");
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goto seccomp_return;
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}
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rc = seccomp_attr_set(ctx, SCMP_FLTATR_CTL_TSYNC, 1);
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if (rc != 0) {
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error_setg_errno(errp, -rc,
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"failed to set seccomp thread synchronization");
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goto seccomp_return;
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}
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for (i = 0; i < ARRAY_SIZE(denylist); i++) {
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uint32_t action;
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if (!(seccomp_opts & denylist[i].set)) {
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continue;
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}
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action = qemu_seccomp_get_action(denylist[i].set);
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rc = seccomp_rule_add_array(ctx, action, denylist[i].num,
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denylist[i].narg, denylist[i].arg_cmp);
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if (rc < 0) {
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error_setg_errno(errp, -rc,
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"failed to add seccomp denylist rules");
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goto seccomp_return;
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}
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}
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rc = seccomp_load(ctx);
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if (rc < 0) {
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error_setg_errno(errp, -rc,
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"failed to load seccomp syscall filter in kernel");
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}
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seccomp_return:
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seccomp_release(ctx);
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return rc < 0 ? -1 : 0;
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}
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int parse_sandbox(void *opaque, QemuOpts *opts, Error **errp)
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{
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if (qemu_opt_get_bool(opts, "enable", false)) {
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uint32_t seccomp_opts = QEMU_SECCOMP_SET_DEFAULT
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| QEMU_SECCOMP_SET_OBSOLETE;
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const char *value = NULL;
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value = qemu_opt_get(opts, "obsolete");
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if (value) {
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if (g_str_equal(value, "allow")) {
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seccomp_opts &= ~QEMU_SECCOMP_SET_OBSOLETE;
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} else if (g_str_equal(value, "deny")) {
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/* this is the default option, this if is here
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* to provide a little bit of consistency for
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* the command line */
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} else {
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error_setg(errp, "invalid argument for obsolete");
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return -1;
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}
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}
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value = qemu_opt_get(opts, "elevateprivileges");
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if (value) {
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if (g_str_equal(value, "deny")) {
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seccomp_opts |= QEMU_SECCOMP_SET_PRIVILEGED;
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} else if (g_str_equal(value, "children")) {
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seccomp_opts |= QEMU_SECCOMP_SET_PRIVILEGED;
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/* calling prctl directly because we're
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* not sure if host has CAP_SYS_ADMIN set*/
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if (prctl(PR_SET_NO_NEW_PRIVS, 1)) {
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error_setg(errp, "failed to set no_new_privs aborting");
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return -1;
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}
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} else if (g_str_equal(value, "allow")) {
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/* default value */
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} else {
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error_setg(errp, "invalid argument for elevateprivileges");
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return -1;
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}
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}
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value = qemu_opt_get(opts, "spawn");
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if (value) {
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if (g_str_equal(value, "deny")) {
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seccomp_opts |= QEMU_SECCOMP_SET_SPAWN;
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} else if (g_str_equal(value, "allow")) {
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/* default value */
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} else {
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error_setg(errp, "invalid argument for spawn");
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return -1;
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}
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}
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value = qemu_opt_get(opts, "resourcecontrol");
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if (value) {
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if (g_str_equal(value, "deny")) {
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seccomp_opts |= QEMU_SECCOMP_SET_RESOURCECTL;
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} else if (g_str_equal(value, "allow")) {
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/* default value */
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} else {
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error_setg(errp, "invalid argument for resourcecontrol");
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return -1;
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}
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}
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if (seccomp_start(seccomp_opts, errp) < 0) {
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return -1;
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}
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}
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return 0;
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}
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static QemuOptsList qemu_sandbox_opts = {
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.name = "sandbox",
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.implied_opt_name = "enable",
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.head = QTAILQ_HEAD_INITIALIZER(qemu_sandbox_opts.head),
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.desc = {
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{
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.name = "enable",
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.type = QEMU_OPT_BOOL,
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},
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{
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.name = "obsolete",
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.type = QEMU_OPT_STRING,
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},
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{
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.name = "elevateprivileges",
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.type = QEMU_OPT_STRING,
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},
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{
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.name = "spawn",
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.type = QEMU_OPT_STRING,
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},
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{
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.name = "resourcecontrol",
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.type = QEMU_OPT_STRING,
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},
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{ /* end of list */ }
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},
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};
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static void seccomp_register(void)
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{
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bool add = false;
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/* FIXME: use seccomp_api_get() >= 2 check when released */
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#if defined(SECCOMP_FILTER_FLAG_TSYNC)
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int check;
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/* check host TSYNC capability, it returns errno == ENOSYS if unavailable */
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check = qemu_seccomp(SECCOMP_SET_MODE_FILTER,
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SECCOMP_FILTER_FLAG_TSYNC, NULL);
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if (check < 0 && errno == EFAULT) {
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add = true;
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}
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#endif
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if (add) {
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qemu_add_opts(&qemu_sandbox_opts);
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}
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}
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opts_init(seccomp_register);
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