syscallfilter: port to libseccomp

5 files changed, 122 insertions, 90 deletions

diff --git a/src/core/build.h b/src/core/build.h
index 4513a0bad7..f04f03f60d 100644
--- a/src/core/build.h
+++ b/src/core/build.h
@@ -81,4 +81,10 @@
 #define _XZ_FEATURE_ "-XZ"
 #endif
 
-#define SYSTEMD_FEATURES _PAM_FEATURE_ " " _LIBWRAP_FEATURE_ " " _AUDIT_FEATURE_ " " _SELINUX_FEATURE_ " " _IMA_FEATURE_ " " _SYSVINIT_FEATURE_ " " _LIBCRYPTSETUP_FEATURE_ " " _GCRYPT_FEATURE_ " " _ACL_FEATURE_ " " _XZ_FEATURE_
+#ifdef HAVE_SECCOMP
+#define _SECCOMP_FEATURE_ "+SECCOMP"
+#else
+#define _SECCOMP_FEATURE_ "-SECCOMP"
+#endif
+
+#define SYSTEMD_FEATURES _PAM_FEATURE_ " " _LIBWRAP_FEATURE_ " " _AUDIT_FEATURE_ " " _SELINUX_FEATURE_ " " _IMA_FEATURE_ " " _SYSVINIT_FEATURE_ " " _LIBCRYPTSETUP_FEATURE_ " " _GCRYPT_FEATURE_ " " _ACL_FEATURE_ " " _XZ_FEATURE_ _SECCOMP_FEATURE_
diff --git a/src/core/dbus-execute.c b/src/core/dbus-execute.c
index db16990233..2ed7a3c73e 100644
--- a/src/core/dbus-execute.c
+++ b/src/core/dbus-execute.c
@@ -25,7 +25,6 @@
 #include "missing.h"
 #include "ioprio.h"
 #include "strv.h"
-#include "syscall-list.h"
 #include "fileio.h"
 #include "execute.h"
 #include "dbus-execute.h"
@@ -354,10 +353,7 @@ static int property_get_syscall_filter(
         assert(reply);
         assert(c);
 
-        if (c->syscall_filter)
-                return sd_bus_message_append_array(reply, 'u', c->syscall_filter, (syscall_max() + 31) >> 4);
-        else
-                return sd_bus_message_append_array(reply, 'u', NULL, 0);
+        return sd_bus_message_append(reply, "s", c->syscall_filter_string);
 }
 
 const sd_bus_vtable bus_exec_vtable[] = {
@@ -422,7 +418,7 @@ const sd_bus_vtable bus_exec_vtable[] = {
         SD_BUS_PROPERTY("SELinuxContext", "s", NULL, offsetof(ExecContext, selinux_context), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("IgnoreSIGPIPE", "b", bus_property_get_bool, offsetof(ExecContext, ignore_sigpipe), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("NoNewPrivileges", "b", bus_property_get_bool, offsetof(ExecContext, no_new_privileges), SD_BUS_VTABLE_PROPERTY_CONST),
-        SD_BUS_PROPERTY("SystemCallFilter", "au", property_get_syscall_filter, 0, SD_BUS_VTABLE_PROPERTY_CONST),
+        SD_BUS_PROPERTY("SystemCallFilter", "s", property_get_syscall_filter, 0, SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_VTABLE_END
 };
 
diff --git a/src/core/execute.c b/src/core/execute.c
index b941a024de..d2e5b740b7 100644
--- a/src/core/execute.c
+++ b/src/core/execute.c
@@ -38,9 +38,13 @@
 #include <linux/fs.h>
 #include <linux/oom.h>
 #include <sys/poll.h>
-#include <linux/seccomp-bpf.h>
 #include <glob.h>
 #include <libgen.h>
+#ifdef HAVE_SECCOMP
+#include <seccomp.h>
+
+#include "set.h"
+#endif
 #undef basename
 
 #ifdef HAVE_PAM
@@ -67,7 +71,6 @@
 #include "utmp-wtmp.h"
 #include "def.h"
 #include "path-util.h"
-#include "syscall-list.h"
 #include "env-util.h"
 #include "fileio.h"
 #include "unit.h"
@@ -933,57 +936,32 @@ static void rename_process_from_path(const char *path) {
         rename_process(process_name);
 }
 
-static int apply_seccomp(uint32_t *syscall_filter) {
-        static const struct sock_filter header[] = {
-                VALIDATE_ARCHITECTURE,
-                EXAMINE_SYSCALL
-        };
-        static const struct sock_filter footer[] = {
-                _KILL_PROCESS
-        };
-
-        int i;
-        unsigned n;
-        struct sock_filter *f;
-        struct sock_fprog prog = {};
-
-        assert(syscall_filter);
+#ifdef HAVE_SECCOMP
+static int apply_seccomp(ExecContext *c) {
+        uint32_t action = SCMP_ACT_ALLOW;
+        Iterator i;
+        void *id;
 
-        /* First: count the syscalls to check for */
-        for (i = 0, n = 0; i < syscall_max(); i++)
-                if (syscall_filter[i >> 4] & (1 << (i & 31)))
-                        n++;
-
-        /* Second: build the filter program from a header the syscall
-         * matches and the footer */
-        f = alloca(sizeof(struct sock_filter) * (ELEMENTSOF(header) + 2*n + ELEMENTSOF(footer)));
-        memcpy(f, header, sizeof(header));
-
-        for (i = 0, n = 0; i < syscall_max(); i++)
-                if (syscall_filter[i >> 4] & (1 << (i & 31))) {
-                        struct sock_filter item[] = {
-                                BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, INDEX_TO_SYSCALL(i), 0, 1),
-                                BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW)
-                        };
+        assert(c);
 
-                        assert_cc(ELEMENTSOF(item) == 2);
+        c->syscall_filter = seccomp_init(c->syscall_filter_default_action);
+        if (!c->syscall_filter)
+                return -1;
 
-                        f[ELEMENTSOF(header) + 2*n]  = item[0];
-                        f[ELEMENTSOF(header) + 2*n+1] = item[1];
+        if (c->syscall_filter_default_action == SCMP_ACT_ALLOW)
+                action = SCMP_ACT_KILL;
 
-                        n++;
+        SET_FOREACH(id, c->filtered_syscalls, i) {
+                int r = seccomp_rule_add(c->syscall_filter, action, PTR_TO_INT(id) - 1, 0);
+                if (r < 0) {
+                        log_error("Failed to add syscall filter");
+                        return r;
                 }
+        }
 
-        memcpy(f + (ELEMENTSOF(header) + 2*n), footer, sizeof(footer));
-
-        /* Third: install the filter */
-        prog.len = ELEMENTSOF(header) + ELEMENTSOF(footer) + 2*n;
-        prog.filter = f;
-        if (prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog) < 0)
-                return -errno;
-
-        return 0;
+        return seccomp_load(c->syscall_filter);
 }
+#endif
 
 static void do_idle_pipe_dance(int idle_pipe[4]) {
         assert(idle_pipe);
@@ -1562,13 +1540,15 @@ int exec_spawn(ExecCommand *command,
                                         goto fail_child;
                                 }
 
-                        if (context->syscall_filter) {
-                                err = apply_seccomp(context->syscall_filter);
+#ifdef HAVE_SECCOMP
+                        if (context->filtered_syscalls) {
+                                err = apply_seccomp(context);
                                 if (err < 0) {
                                         r = EXIT_SECCOMP;
                                         goto fail_child;
                                 }
                         }
+#endif
 #ifdef HAVE_SELINUX
                         if (context->selinux_context && use_selinux()) {
                                 bool ignore;
@@ -1751,6 +1731,18 @@ void exec_context_done(ExecContext *c) {
 
         free(c->syscall_filter);
         c->syscall_filter = NULL;
+
+        free(c->syscall_filter_string);
+        c->syscall_filter_string = NULL;
+
+#ifdef HAVE_SECCOMP
+        if (c->syscall_filter) {
+                seccomp_release(c->syscall_filter);
+                c->syscall_filter = NULL;
+        }
+        set_free(c->filtered_syscalls);
+        c->filtered_syscalls = NULL;
+#endif
 }
 
 void exec_command_done(ExecCommand *c) {
diff --git a/src/core/execute.h b/src/core/execute.h
index be811a97c1..b2d70d7d86 100644
--- a/src/core/execute.h
+++ b/src/core/execute.h
@@ -33,6 +33,11 @@ typedef struct ExecRuntime ExecRuntime;
 #include <stdbool.h>
 #include <stdio.h>
 #include <sched.h>
+#ifdef HAVE_SECCOMP
+#include <seccomp.h>
+
+#include "set.h"
+#endif
 
 #include "list.h"
 #include "util.h"
@@ -162,7 +167,12 @@ struct ExecContext {
          * don't enter a trigger loop. */
         bool same_pgrp;
 
-        uint32_t *syscall_filter;
+#ifdef HAVE_SECCOMP
+        scmp_filter_ctx syscall_filter;
+        Set *filtered_syscalls;
+        uint32_t syscall_filter_default_action;
+#endif
+        char *syscall_filter_string;
 
         bool oom_score_adjust_set:1;
         bool nice_set:1;
diff --git a/src/core/load-fragment.c b/src/core/load-fragment.c
index 7a2d32ddbd..06ff18b573 100644
--- a/src/core/load-fragment.c
+++ b/src/core/load-fragment.c
@@ -33,6 +33,11 @@
 #include <sys/stat.h>
 #include <sys/time.h>
 #include <sys/resource.h>
+#ifdef HAVE_SECCOMP
+#include <seccomp.h>
+
+#include "set.h"
+#endif
 
 #include "sd-messages.h"
 #include "unit.h"
@@ -47,13 +52,12 @@
 #include "unit-printf.h"
 #include "utf8.h"
 #include "path-util.h"
-#include "syscall-list.h"
 #include "env-util.h"
 #include "cgroup.h"
 #include "bus-util.h"
 #include "bus-error.h"
 
-#ifndef HAVE_SYSV_COMPAT
+#if !defined(HAVE_SYSV_COMPAT) || !defined(HAVE_SECCOMP)
 int config_parse_warn_compat(const char *unit,
                              const char *filename,
                              unsigned line,
@@ -1916,16 +1920,7 @@ int config_parse_documentation(const char *unit,
         return r;
 }
 
-static void syscall_set(uint32_t *p, int nr) {
-        nr = SYSCALL_TO_INDEX(nr);
-        p[nr >> 4] |= 1 << (nr & 31);
-}
-
-static void syscall_unset(uint32_t *p, int nr) {
-        nr = SYSCALL_TO_INDEX(nr);
-        p[nr >> 4] &= ~(1 << (nr & 31));
-}
-
+#ifdef HAVE_SECCOMP
 int config_parse_syscall_filter(const char *unit,
                                 const char *filename,
                                 unsigned line,
@@ -1936,13 +1931,23 @@ int config_parse_syscall_filter(const char *unit,
                                 const char *rvalue,
                                 void *data,
                                 void *userdata) {
-
         ExecContext *c = data;
         Unit *u = userdata;
         bool invert = false;
         char *w;
         size_t l;
         char *state;
+        _cleanup_strv_free_ char **syscalls = strv_new(NULL, NULL);
+        _cleanup_free_ char *sorted_syscalls = NULL;
+        uint32_t action = SCMP_ACT_ALLOW;
+        Iterator i;
+        void *e;
+        static char const *default_syscalls[] = {"execve",
+                                                 "exit",
+                                                 "exit_group",
+                                                 "rt_sigreturn",
+                                                 "sigreturn",
+                                                 NULL};
 
         assert(filename);
         assert(lvalue);
@@ -1951,34 +1956,37 @@ int config_parse_syscall_filter(const char *unit,
 
         if (isempty(rvalue)) {
                 /* Empty assignment resets the list */
-                free(c->syscall_filter);
-                c->syscall_filter = NULL;
+                set_free(c->filtered_syscalls);
+                c->filtered_syscalls= NULL;
+                free(c->syscall_filter_string);
+                c->syscall_filter_string = NULL;
                 return 0;
         }
 
         if (rvalue[0] == '~') {
                 invert = true;
+                action = SCMP_ACT_KILL;
                 rvalue++;
         }
 
-        if (!c->syscall_filter) {
-                size_t n;
+        if (!c->filtered_syscalls) {
+                c->filtered_syscalls = set_new(trivial_hash_func, trivial_compare_func);
+                if (invert)
+                        c->syscall_filter_default_action = SCMP_ACT_ALLOW;
+                else {
+                        char const **syscall;
 
-                n = (syscall_max() + 31) >> 4;
-                c->syscall_filter = new(uint32_t, n);
-                if (!c->syscall_filter)
-                        return log_oom();
+                        c->syscall_filter_default_action = SCMP_ACT_KILL;
 
-                memset(c->syscall_filter, invert ? 0xFF : 0, n * sizeof(uint32_t));
+                        /* accept default syscalls if we are on a whitelist */
+                        STRV_FOREACH(syscall, default_syscalls) {
+                                int id = seccomp_syscall_resolve_name(*syscall);
+                                if (id < 0)
+                                        continue;
 
-                /* Add these by default */
-                syscall_set(c->syscall_filter, __NR_execve);
-                syscall_set(c->syscall_filter, __NR_rt_sigreturn);
-#ifdef __NR_sigreturn
-                syscall_set(c->syscall_filter, __NR_sigreturn);
-#endif
-                syscall_set(c->syscall_filter, __NR_exit_group);
-                syscall_set(c->syscall_filter, __NR_exit);
+                                set_replace(c->filtered_syscalls, INT_TO_PTR(id + 1));
+                        }
+                }
         }
 
         FOREACH_WORD_QUOTED(w, l, rvalue, state) {
@@ -1989,23 +1997,39 @@ int config_parse_syscall_filter(const char *unit,
                 if (!t)
                         return log_oom();
 
-                id = syscall_from_name(t);
+                id = seccomp_syscall_resolve_name(t);
                 if (id < 0)  {
                         log_syntax(unit, LOG_ERR, filename, line, EINVAL,
                                    "Failed to parse syscall, ignoring: %s", t);
                         continue;
                 }
 
-                if (invert)
-                        syscall_unset(c->syscall_filter, id);
+                /* If we previously wanted to forbid a syscall
+                 * and now we want to allow it, then remove it from the list
+                 * libseccomp will also return -EPERM if we try to add
+                 * a rule with the same action as the default
+                 */
+                if (action == c->syscall_filter_default_action)
+                        set_remove(c->filtered_syscalls, INT_TO_PTR(id + 1));
                 else
-                        syscall_set(c->syscall_filter, id);
+                        set_replace(c->filtered_syscalls, INT_TO_PTR(id + 1));
+        }
+
+        SET_FOREACH(e, c->filtered_syscalls, i) {
+                char *name = seccomp_syscall_resolve_num_arch(SCMP_ARCH_NATIVE, PTR_TO_INT(e) - 1);
+                strv_push(&syscalls, name);
         }
 
+        sorted_syscalls = strv_join(strv_sort(syscalls), " ");
+        if (invert)
+                c->syscall_filter_string = strv_join(STRV_MAKE("~", sorted_syscalls, NULL), "");
+        else
+                c->syscall_filter_string = strdup(sorted_syscalls);
         c->no_new_privileges = true;
 
         return 0;
 }
+#endif
 
 int config_parse_unit_slice(
                 const char *unit,
@@ -2778,7 +2802,11 @@ void unit_dump_config_items(FILE *f) {
                 { config_parse_set_status,            "STATUS" },
                 { config_parse_service_sockets,       "SOCKETS" },
                 { config_parse_environ,               "ENVIRON" },
+#ifdef HAVE_SECCOMP
                 { config_parse_syscall_filter,        "SYSCALL" },
+#else
+                { config_parse_warn_compat,           "NOTSUPPORTED" },
+#endif
                 { config_parse_cpu_shares,            "SHARES" },
                 { config_parse_memory_limit,          "LIMIT" },
                 { config_parse_device_allow,          "DEVICE" },