seccomp: on s390 the clone() parameters are reversed

Add a bit of code that tries to get the right parameter order in place
for some of the better known architectures, and skips
restrict_namespaces for other archs.

This also bypasses the test on archs where we don't know the right
order.

In this case I didn't bother with testing the case where no filter is
applied, since that is hopefully just an issue for now, as there's
nothing stopping us from supporting more archs, we just need to know
which order is right.

Fixes: #5241

5 files changed, 55 insertions, 13 deletions

diff --git a/man/systemd.exec.xml b/man/systemd.exec.xml
index fd47b0a20a..e7e5d6b0c7 100644
--- a/man/systemd.exec.xml
+++ b/man/systemd.exec.xml
@@ -1554,11 +1554,10 @@
         <citerefentry><refentrytitle>setns</refentrytitle><manvolnum>2</manvolnum></citerefentry> system calls, taking
         the specified flags parameters into account. Note that — if this option is used — in addition to restricting
         creation and switching of the specified types of namespaces (or all of them, if true) access to the
-        <function>setns()</function> system call with a zero flags parameter is prohibited.
-        If running in user mode, or in system mode, but without the <constant>CAP_SYS_ADMIN</constant>
-        capability (e.g. setting <varname>User=</varname>), <varname>NoNewPrivileges=yes</varname>
-        is implied.
-        </para></listitem>
+        <function>setns()</function> system call with a zero flags parameter is prohibited.  This setting is only
+        supported on x86, x86-64, s390 and s390x, and enforces no restrictions on other architectures. If running in user
+        mode, or in system mode, but without the <constant>CAP_SYS_ADMIN</constant> capability (e.g. setting
+        <varname>User=</varname>), <varname>NoNewPrivileges=yes</varname> is implied.  </para></listitem>
       </varlistentry>
 
       <varlistentry>
diff --git a/src/basic/raw-clone.h b/src/basic/raw-clone.h
index d473828999..c6e531ada4 100644
--- a/src/basic/raw-clone.h
+++ b/src/basic/raw-clone.h
@@ -47,8 +47,8 @@
 static inline int raw_clone(unsigned long flags) {
         assert((flags & (CLONE_VM|CLONE_PARENT_SETTID|CLONE_CHILD_SETTID|
                          CLONE_CHILD_CLEARTID|CLONE_SETTLS)) == 0);
-#if defined(__s390__) || defined(__CRIS__)
-        /* On s390 and cris the order of the first and second arguments
+#if defined(__s390x__) || defined(__s390__) || defined(__CRIS__)
+        /* On s390/s390x and cris the order of the first and second arguments
          * of the raw clone() system call is reversed. */
         return (int) syscall(__NR_clone, NULL, flags);
 #elif defined(__sparc__) && defined(__arch64__)
diff --git a/src/shared/seccomp-util.c b/src/shared/seccomp-util.c
index 44706669b4..e35f18471c 100644
--- a/src/shared/seccomp-util.c
+++ b/src/shared/seccomp-util.c
@@ -750,10 +750,35 @@ int seccomp_restrict_namespaces(unsigned long retain) {
 
         SECCOMP_FOREACH_LOCAL_ARCH(arch) {
                 _cleanup_(seccomp_releasep) scmp_filter_ctx seccomp = NULL;
+                int clone_reversed_order = -1;
                 unsigned i;
 
                 log_debug("Operating on architecture: %s", seccomp_arch_to_string(arch));
 
+                switch (arch) {
+
+                case SCMP_ARCH_X86_64:
+                case SCMP_ARCH_X86:
+                case SCMP_ARCH_X32:
+                        clone_reversed_order = 0;
+                        break;
+
+                case SCMP_ARCH_S390:
+                case SCMP_ARCH_S390X:
+                        /* On s390/s390x the first two parameters to clone are switched */
+                        clone_reversed_order = 1;
+                        break;
+
+                /* Please add more definitions here, if you port systemd to other architectures! */
+
+#if !defined(__i386__) && !defined(__x86_64__) && !defined(__s390__) && !defined(__s390x__)
+#warning "Consider adding the right clone() syscall definitions here!"
+#endif
+                }
+
+                if (clone_reversed_order < 0) /* we don't know the right order, let's ignore this arch... */
+                        continue;
+
                 r = seccomp_init_for_arch(&seccomp, arch, SCMP_ACT_ALLOW);
                 if (r < 0)
                         return r;
@@ -802,12 +827,20 @@ int seccomp_restrict_namespaces(unsigned long retain) {
                                 break;
                         }
 
-                        r = seccomp_rule_add_exact(
-                                        seccomp,
-                                        SCMP_ACT_ERRNO(EPERM),
-                                        SCMP_SYS(clone),
-                                        1,
-                                        SCMP_A0(SCMP_CMP_MASKED_EQ, f, f));
+                        if (clone_reversed_order == 0)
+                                r = seccomp_rule_add_exact(
+                                                seccomp,
+                                                SCMP_ACT_ERRNO(EPERM),
+                                                SCMP_SYS(clone),
+                                                1,
+                                                SCMP_A0(SCMP_CMP_MASKED_EQ, f, f));
+                        else
+                                r = seccomp_rule_add_exact(
+                                                seccomp,
+                                                SCMP_ACT_ERRNO(EPERM),
+                                                SCMP_SYS(clone),
+                                                1,
+                                                SCMP_A1(SCMP_CMP_MASKED_EQ, f, f));
                         if (r < 0) {
                                 log_debug_errno(r, "Failed to add clone() rule for architecture %s, skipping: %m", seccomp_arch_to_string(arch));
                                 break;
diff --git a/src/shared/seccomp-util.h b/src/shared/seccomp-util.h
index bfbfb5ab3d..61f94de638 100644
--- a/src/shared/seccomp-util.h
+++ b/src/shared/seccomp-util.h
@@ -91,6 +91,13 @@ int seccomp_memory_deny_write_execute(void);
 #define SECCOMP_MEMORY_DENY_WRITE_EXECUTE_BROKEN 1
 #endif
 
+/* we don't know the right order of the clone() parameters except for these archs, for now */
+#if defined(__x86_64__) || defined(__i386__) || defined(__s390x__) || defined(__s390__)
+#define SECCOMP_RESTRICT_NAMESPACES_BROKEN 0
+#else
+#define SECCOMP_RESTRICT_NAMESPACES_BROKEN 1
+#endif
+
 extern const uint32_t seccomp_local_archs[];
 
 #define SECCOMP_FOREACH_LOCAL_ARCH(arch) \
diff --git a/src/test/test-seccomp.c b/src/test/test-seccomp.c
index 3659238810..34a1275162 100644
--- a/src/test/test-seccomp.c
+++ b/src/test/test-seccomp.c
@@ -158,6 +158,8 @@ static void test_restrict_namespace(void) {
         assert_se(streq(s, "cgroup ipc net mnt pid user uts"));
         assert_se(namespace_flag_from_string_many(s, &ul) == 0 && ul == NAMESPACE_FLAGS_ALL);
 
+#if SECCOMP_RESTRICT_NAMESPACES_BROKEN == 0
+
         if (!is_seccomp_available())
                 return;
         if (geteuid() != 0)
@@ -216,6 +218,7 @@ static void test_restrict_namespace(void) {
         }
 
         assert_se(wait_for_terminate_and_warn("nsseccomp", pid, true) == EXIT_SUCCESS);
+#endif
 }
 
 static void test_protect_sysctl(void) {