469830d142
This substantially reworks the seccomp code, to ensure better compatibility with some architectures, including i386. So far we relied on libseccomp's internal handling of the multiple syscall ABIs supported on Linux. This is problematic however, as it does not define clear semantics if an ABI is not able to support specific seccomp rules we install. This rework hence changes a couple of things: - We no longer use seccomp_rule_add(), but only seccomp_rule_add_exact(), and fail the installation of a filter if the architecture doesn't support it. - We no longer rely on adding multiple syscall architectures to a single filter, but instead install a separate filter for each syscall architecture supported. This way, we can install a strict filter for x86-64, while permitting a less strict filter for i386. - All high-level filter additions are now moved from execute.c to seccomp-util.c, so that we can test them independently of the service execution logic. - Tests have been added for all types of our seccomp filters. - SystemCallFilters= and SystemCallArchitectures= are now implemented in independent filters and installation logic, as they semantically are very much independent of each other. Fixes: #4575
199 lines
9 KiB
C
199 lines
9 KiB
C
/***
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This file is part of systemd.
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Copyright 2016 Lennart Poettering
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systemd is free software; you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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systemd is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with systemd; If not, see <http://www.gnu.org/licenses/>.
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***/
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#include <errno.h>
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#include <linux/netlink.h>
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#include <sys/capability.h>
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#include <sys/types.h>
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#ifdef HAVE_SECCOMP
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#include <seccomp.h>
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#endif
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#include "alloc-util.h"
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#include "log.h"
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#include "nspawn-seccomp.h"
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#ifdef HAVE_SECCOMP
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#include "seccomp-util.h"
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#endif
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#include "string-util.h"
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#ifdef HAVE_SECCOMP
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static int seccomp_add_default_syscall_filter(
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scmp_filter_ctx ctx,
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uint32_t arch,
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uint64_t cap_list_retain) {
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static const struct {
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uint64_t capability;
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int syscall_num;
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} blacklist[] = {
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{ 0, SCMP_SYS(_sysctl) }, /* obsolete syscall */
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{ 0, SCMP_SYS(add_key) }, /* keyring is not namespaced */
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{ 0, SCMP_SYS(afs_syscall) }, /* obsolete syscall */
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{ 0, SCMP_SYS(bdflush) },
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#ifdef __NR_bpf
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{ 0, SCMP_SYS(bpf) },
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#endif
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{ 0, SCMP_SYS(break) }, /* obsolete syscall */
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{ 0, SCMP_SYS(create_module) }, /* obsolete syscall */
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{ 0, SCMP_SYS(ftime) }, /* obsolete syscall */
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{ 0, SCMP_SYS(get_kernel_syms) }, /* obsolete syscall */
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{ 0, SCMP_SYS(getpmsg) }, /* obsolete syscall */
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{ 0, SCMP_SYS(gtty) }, /* obsolete syscall */
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#ifdef __NR_kexec_file_load
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{ 0, SCMP_SYS(kexec_file_load) },
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#endif
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{ 0, SCMP_SYS(kexec_load) },
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{ 0, SCMP_SYS(keyctl) }, /* keyring is not namespaced */
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{ 0, SCMP_SYS(lock) }, /* obsolete syscall */
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{ 0, SCMP_SYS(lookup_dcookie) },
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{ 0, SCMP_SYS(mpx) }, /* obsolete syscall */
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{ 0, SCMP_SYS(nfsservctl) }, /* obsolete syscall */
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{ 0, SCMP_SYS(open_by_handle_at) },
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{ 0, SCMP_SYS(perf_event_open) },
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{ 0, SCMP_SYS(prof) }, /* obsolete syscall */
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{ 0, SCMP_SYS(profil) }, /* obsolete syscall */
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{ 0, SCMP_SYS(putpmsg) }, /* obsolete syscall */
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{ 0, SCMP_SYS(query_module) }, /* obsolete syscall */
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{ 0, SCMP_SYS(quotactl) },
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{ 0, SCMP_SYS(request_key) }, /* keyring is not namespaced */
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{ 0, SCMP_SYS(security) }, /* obsolete syscall */
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{ 0, SCMP_SYS(sgetmask) }, /* obsolete syscall */
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{ 0, SCMP_SYS(ssetmask) }, /* obsolete syscall */
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{ 0, SCMP_SYS(stty) }, /* obsolete syscall */
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{ 0, SCMP_SYS(swapoff) },
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{ 0, SCMP_SYS(swapon) },
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{ 0, SCMP_SYS(sysfs) }, /* obsolete syscall */
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{ 0, SCMP_SYS(tuxcall) }, /* obsolete syscall */
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{ 0, SCMP_SYS(ulimit) }, /* obsolete syscall */
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{ 0, SCMP_SYS(uselib) }, /* obsolete syscall */
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{ 0, SCMP_SYS(ustat) }, /* obsolete syscall */
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{ 0, SCMP_SYS(vserver) }, /* obsolete syscall */
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{ CAP_SYSLOG, SCMP_SYS(syslog) },
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{ CAP_SYS_MODULE, SCMP_SYS(delete_module) },
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{ CAP_SYS_MODULE, SCMP_SYS(finit_module) },
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{ CAP_SYS_MODULE, SCMP_SYS(init_module) },
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{ CAP_SYS_PACCT, SCMP_SYS(acct) },
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{ CAP_SYS_PTRACE, SCMP_SYS(process_vm_readv) },
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{ CAP_SYS_PTRACE, SCMP_SYS(process_vm_writev) },
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{ CAP_SYS_PTRACE, SCMP_SYS(ptrace) },
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{ CAP_SYS_RAWIO, SCMP_SYS(ioperm) },
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{ CAP_SYS_RAWIO, SCMP_SYS(iopl) },
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{ CAP_SYS_RAWIO, SCMP_SYS(pciconfig_iobase) },
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{ CAP_SYS_RAWIO, SCMP_SYS(pciconfig_read) },
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{ CAP_SYS_RAWIO, SCMP_SYS(pciconfig_write) },
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#ifdef __NR_s390_pci_mmio_read
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{ CAP_SYS_RAWIO, SCMP_SYS(s390_pci_mmio_read) },
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#endif
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#ifdef __NR_s390_pci_mmio_write
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{ CAP_SYS_RAWIO, SCMP_SYS(s390_pci_mmio_write) },
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#endif
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{ CAP_SYS_TIME, SCMP_SYS(adjtimex) },
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{ CAP_SYS_TIME, SCMP_SYS(clock_adjtime) },
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{ CAP_SYS_TIME, SCMP_SYS(clock_settime) },
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{ CAP_SYS_TIME, SCMP_SYS(settimeofday) },
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{ CAP_SYS_TIME, SCMP_SYS(stime) },
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};
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unsigned i;
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int r, c = 0;
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for (i = 0; i < ELEMENTSOF(blacklist); i++) {
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if (blacklist[i].capability != 0 && (cap_list_retain & (1ULL << blacklist[i].capability)))
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continue;
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r = seccomp_rule_add_exact(ctx, SCMP_ACT_ERRNO(EPERM), blacklist[i].syscall_num, 0);
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if (r < 0) {
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/* If the system call is not known on this architecture, then that's fine, let's ignore it */
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_cleanup_free_ char *n = NULL;
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n = seccomp_syscall_resolve_num_arch(arch, blacklist[i].syscall_num);
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log_debug_errno(r, "Failed to add rule for system call %s, ignoring: %m", strna(n));
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} else
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c++;
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}
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return c;
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}
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int setup_seccomp(uint64_t cap_list_retain) {
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uint32_t arch;
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int r;
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if (!is_seccomp_available()) {
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log_debug("SECCOMP features not detected in the kernel, disabling SECCOMP audit filter");
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return 0;
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}
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SECCOMP_FOREACH_LOCAL_ARCH(arch) {
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_cleanup_(seccomp_releasep) scmp_filter_ctx seccomp = NULL;
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int n;
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log_debug("Operating on architecture: %s", seccomp_arch_to_string(arch));
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r = seccomp_init_for_arch(&seccomp, arch, SCMP_ACT_ALLOW);
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if (r < 0)
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return log_error_errno(r, "Failed to allocate seccomp object: %m");
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n = seccomp_add_default_syscall_filter(seccomp, arch, cap_list_retain);
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if (n < 0)
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return n;
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/*
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Audit is broken in containers, much of the userspace audit hookup will fail if running inside a
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container. We don't care and just turn off creation of audit sockets.
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This will make socket(AF_NETLINK, *, NETLINK_AUDIT) fail with EAFNOSUPPORT which audit userspace uses
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as indication that audit is disabled in the kernel.
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*/
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r = seccomp_rule_add_exact(
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seccomp,
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SCMP_ACT_ERRNO(EAFNOSUPPORT),
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SCMP_SYS(socket),
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2,
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SCMP_A0(SCMP_CMP_EQ, AF_NETLINK),
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SCMP_A2(SCMP_CMP_EQ, NETLINK_AUDIT));
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if (r < 0)
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log_debug_errno(r, "Failed to add audit seccomp rule, ignoring: %m");
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else
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n++;
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if (n <= 0) /* no rule added? then skip this architecture */
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continue;
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r = seccomp_load(seccomp);
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if (IN_SET(r, -EPERM, -EACCES))
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return log_error_errno(r, "Failed to install seccomp audit filter: %m");
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if (r < 0)
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log_debug_errno(r, "Failed to install filter set for architecture %s, skipping: %m", seccomp_arch_to_string(arch));
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}
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return 0;
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}
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#else
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int setup_seccomp(uint64_t cap_list_retain) {
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return 0;
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}
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#endif
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