exec: Add kill action to system call filters

Define explicit action "kill" for SystemCallErrorNumber=.

In addition to errno code, allow specifying "kill" as action for
SystemCallFilter=.

---
v7: seccomp_parse_errno_or_action() returns -EINVAL if !HAVE_SECCOMP
v6: use streq_ptr(), let errno_to_name() handle bad values, kill processes,
 init syscall_errno
v5: actually use seccomp_errno_or_action_to_string(), don't fail bus unit
parsing without seccomp
v4: fix build without seccomp
v3: drop log action
v2: action -> number

src/basic/parse-util.c

@@ -16,6 +16,9 @@
 #include "missing_network.h"
 #include "parse-util.h"
 #include "process-util.h"
+#if HAVE_SECCOMP
+#include "seccomp-util.h"
+#endif
 #include "stat-util.h"
 #include "string-util.h"
 #include "strv.h"
@@ -314,6 +317,7 @@ int parse_errno(const char *t) {
         return e;
 }
 
+#if HAVE_SECCOMP
 int parse_syscall_and_errno(const char *in, char **name, int *error) {
         _cleanup_free_ char *n = NULL;
         char *p;
@@ -332,7 +336,7 @@ int parse_syscall_and_errno(const char *in, char **name, int *error) {
 
         p = strchr(in, ':');
         if (p) {
-                e = parse_errno(p + 1);
+                e = seccomp_parse_errno_or_action(p + 1);
                 if (e < 0)
                         return e;
 
@@ -351,6 +355,7 @@ int parse_syscall_and_errno(const char *in, char **name, int *error) {
 
         return 0;
 }
+#endif
 
 static const char *mangle_base(const char *s, unsigned *base) {
         const char *k;