api: create an API level construct as part of the supported APIworking-api_level

WORK IN PROGRESS, DO NOT SHIP

XXX - manpage needed
XXX - tests needed

Signed-off-by: Paul Moore <paul@paul-moore.com>

4 files changed, 98 insertions, 3 deletions

diff --git a/include/seccomp.h.in b/include/seccomp.h.in
index 5843639..85b08b8 100644
--- a/include/seccomp.h.in
+++ b/include/seccomp.h.in
@@ -275,6 +275,16 @@ struct scmp_arg_cmp {
 const struct scmp_version *seccomp_version(void);
 
 /**
+ * XXX
+ */
+const unsigned int seccomp_api_get(void);
+
+/**
+ * XXX
+ */
+int seccomp_api_set(unsigned int level);
+
+/**
  * Initialize the filter state
  * @param def_action the default filter action
  *
diff --git a/src/api.c b/src/api.c
index 5cc04d2..8a38d00 100644
--- a/src/api.c
+++ b/src/api.c
@@ -44,6 +44,8 @@ const struct scmp_version library_version = {
 	.micro = SCMP_VER_MICRO,
 };
 
+unsigned int seccomp_api_level = 0;
+
 /**
  * Validate a filter context
  * @param ctx the filter context
@@ -75,6 +77,30 @@ static int _syscall_valid(const struct db_filter_col *col, int syscall)
 	return 0;
 }
 
+/**
+ * Update the API level
+ *
+ * XXX
+ */
+static void _seccomp_api_update(void)
+{
+	unsigned int level = 1;
+
+	/* if seccomp_api_level > 0 then it's already been set, we're done */
+	if (seccomp_api_level >= 1)
+		return;
+
+	/* NOTE: level 1 is the base level, start checking at 2 */
+
+	/* level 2 */
+	if (sys_chk_seccomp_syscall() &&
+	    sys_chk_seccomp_flag(SECCOMP_FILTER_FLAG_TSYNC))
+		level = 2;
+
+	/* update the stored api level */
+	seccomp_api_level = level;
+}
+
 /* NOTE - function header comment in include/seccomp.h */
 API const struct scmp_version *seccomp_version(void)
 {
@@ -82,6 +108,35 @@ API const struct scmp_version *seccomp_version(void)
 }
 
 /* NOTE - function header comment in include/seccomp.h */
+API const unsigned int seccomp_api_get(void)
+{
+	/* update the api level, if needed */
+	_seccomp_api_update();
+
+	return seccomp_api_level;
+}
+
+/* NOTE - function header comment in include/seccomp.h */
+API int seccomp_api_set(unsigned int level)
+{
+	switch (level) {
+	case 1:
+		sys_set_seccomp_syscall(false);
+		sys_set_seccomp_flag(SECCOMP_FILTER_FLAG_TSYNC, false);
+		break;
+	case 2:
+		sys_set_seccomp_syscall(true);
+		sys_set_seccomp_flag(SECCOMP_FILTER_FLAG_TSYNC, true);
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	seccomp_api_level = level;
+	return 0;
+}
+
+/* NOTE - function header comment in include/seccomp.h */
 API scmp_filter_ctx seccomp_init(uint32_t def_action)
 {
 	if (db_action_valid(def_action) < 0)
diff --git a/src/system.c b/src/system.c
index c0a1adc..f79943a 100644
--- a/src/system.c
+++ b/src/system.c
@@ -40,6 +40,7 @@
 
 static int _nr_seccomp = -1;
 static int _support_seccomp_syscall = -1;
+static int _support_seccomp_flag_tsync = -1;
 
 /**
  * Check to see if the seccomp() syscall is supported
@@ -98,25 +99,51 @@ supported:
 }
 
 /**
+ * XXX
+ */
+void sys_set_seccomp_syscall(bool enable)
+{
+	_support_seccomp_syscall = (enable ? 1 : 0);
+}
+
+/**
  * Check to see if a seccomp() flag is supported
  * @param flag the seccomp() flag
  *
  * This function checks to see if a seccomp() flag is supported by the system.
- * If the flag is supported one is returned, zero if unsupported, negative
- * values on error.
+ * Return one if the syscall is supported, zero if unsupported, negative values
+ * on error.
  *
  */
 int sys_chk_seccomp_flag(int flag)
 {
+	int rc;
+
 	switch (flag) {
 	case SECCOMP_FILTER_FLAG_TSYNC:
-		return sys_chk_seccomp_syscall();
+		if (_support_seccomp_flag_tsync < 0) {
+			rc = sys_chk_seccomp_syscall();
+			_support_seccomp_flag_tsync = (rc == 1 ? 1 : 0);
+		}
+		return _support_seccomp_flag_tsync;
 	}
 
 	return -EOPNOTSUPP;
 }
 
 /**
+ * XXX
+ */
+void sys_set_seccomp_flag(int flag, bool enable)
+{
+	switch (flag) {
+	case SECCOMP_FILTER_FLAG_TSYNC:
+		_support_seccomp_flag_tsync = (enable ? 1 : 0);
+		break;
+	}
+}
+
+/**
  * Loads the filter into the kernel
  * @param col the filter collection
  *
diff --git a/src/system.h b/src/system.h
index eea9973..0e2cd82 100644
--- a/src/system.h
+++ b/src/system.h
@@ -109,7 +109,10 @@ typedef struct sock_filter bpf_instr_raw;
 #endif
 
 int sys_chk_seccomp_syscall(void);
+void sys_set_seccomp_syscall(bool enable);
+
 int sys_chk_seccomp_flag(int flag);
+void sys_set_seccomp_flag(int flag, bool enable);
 
 int sys_filter_load(const struct db_filter_col *col);