cmd/snap-confine: add sc_init_invocation()

The new helper function handles initialization of sc_invocation,
which mostly involves internal consistency checks.

Signed-off-by: Zygmunt Krynicki <zygmunt.krynicki@canonical.com>

cmd/Makefile.am

@@ -226,6 +226,8 @@ snap_confine_snap_confine_SOURCES = \
 	snap-confine/ns-support.h \
 	snap-confine/snap-confine-args.c \
 	snap-confine/snap-confine-args.h \
+	snap-confine/snap-confine-invocation.c \
+	snap-confine/snap-confine-invocation.h \
 	snap-confine/snap-confine-invocation.h \
 	snap-confine/snap-confine.c \
 	snap-confine/udev-support.c \

cmd/snap-confine/snap-confine-invocation.c

@@ -0,0 +1,71 @@
+/*
+ * Copyright (C) 2019 Canonical Ltd
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 3 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include "snap-confine-invocation.h"
+
+#include <string.h>
+
+#include "../libsnap-confine-private/snap.h"
+#include "../libsnap-confine-private/utils.h"
+
+void sc_init_invocation(sc_invocation * inv, const struct sc_args *args,
+			const char *snap_instance)
+{
+	/* Snap instance name is conveyed via untrusted environment. It may be
+	 * unset (typically when experimenting with snap-confine by hand). It
+	 * must also be a valid snap instance name. */
+	if (snap_instance == NULL) {
+		die("SNAP_INSTANCE_NAME is not set");
+	}
+	sc_instance_name_validate(snap_instance, NULL);
+
+	/* The security tag is conveyed via untrusted command line. It must be
+	 * in agreement with snap instance name and must be a valid security
+	 * tag. */
+	const char *security_tag = sc_args_security_tag(args);
+	if (!verify_security_tag(security_tag, snap_instance)) {
+		die("security tag %s not allowed", security_tag);
+	}
+
+	/* The base snap name is conveyed via untrusted, optional, command line
+	 * argument. It may be omitted where it implies the "core" snap is the
+	 * base. */
+	const char *base_snap_name = sc_args_base_snap(args) ? : "core";
+	sc_snap_name_validate(base_snap_name, NULL);
+
+	/* The executable is conveyed via untrusted command lne. It must be set
+	 * but cannot be validated further than that at this time. It might be
+	 * arguable to validate it to be snap-exec in one of the well-known
+	 * locations or one of the special-cases like strace / gdb but this is
+	 * not done at this time. */
+	const char *executable = sc_args_executable(args);
+	/* TODO: validate NULL */
+
+	/* Invocation helps to pass relevant data to various parts of snap-confine. */
+	memset(inv, 0, sizeof *inv);
+	inv->base_snap_name = base_snap_name;
+	inv->executable = executable;
+	inv->security_tag = security_tag;
+	inv->snap_instance = snap_instance;
+	inv->classic_confinement = sc_args_is_classic_confinement(args);
+
+	debug("security tag: %s", inv->security_tag);
+	debug("executable:   %s", inv->executable);
+	debug("confinement:  %s",
+	      inv->classic_confinement ? "classic" : "non-classic");
+	debug("base snap:    %s", inv->base_snap_name);
+}

cmd/snap-confine/snap-confine-invocation.h

@@ -20,6 +20,8 @@
 
 #include <stdbool.h>
 
+#include "snap-confine-args.h"
+
 /**
  * sc_invocation contains information about how snap-confine was invoked.
  *
@@ -36,4 +38,14 @@ typedef struct sc_invocation {
 	bool is_normal_mode;
 } sc_invocation;
 
+/**
+ * sc_init_invocation initializes the invocation object.
+ *
+ * Invocation is constructed based on command line arguments as well as
+ * environment value (SNAP_INSTANCE_NAME). All input is untrustee and is
+ * validated internally.
+ **/
+void sc_init_invocation(sc_invocation * inv, const struct sc_args *args,
+			const char *snap_instance);
+
 #endif