lsm: add a --lsm-profile flag

In LXD, we use the container name in the LSM profile. If the container name
is changed on migrate (on the host side), we want to use a different LSM
profile name (a. la. --cgroup-root). This flag adds that support.

v2: remove unused field, add comment about double detection in
    kerndat_lsm()
Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

cr-restore.c

@@ -2827,29 +2827,35 @@ static int sigreturn_restore(pid_t pid, CoreEntry *core)
 	if (!creds)
 		goto err;
 
-	if (creds->lsm_profile) {
-		char *rendered;
+	if (creds->lsm_profile || opts.lsm_supplied) {
+		char *rendered, *profile;
 		int ret;
 
-		if (validate_lsm(creds) < 0)
+		profile = creds->lsm_profile;
+		if (opts.lsm_supplied)
+			profile = opts.lsm_profile;
+
+		if (validate_lsm(profile) < 0)
 			return -1;
 
-		ret = render_lsm_profile(creds->lsm_profile, &rendered);
-		if (ret < 0) {
-			goto err_nv;
-		}
+		if (profile) {
+			ret = render_lsm_profile(profile, &rendered);
+			if (ret < 0) {
+				goto err_nv;
+			}
+
+			lsm_pos = rst_mem_cpos(RM_PRIVATE);
+			lsm_profile_len = strlen(rendered);
+			lsm = rst_mem_alloc(lsm_profile_len + 1, RM_PRIVATE);
+			if (!lsm) {
+				xfree(rendered);
+				goto err_nv;
+			}
 
-		lsm_pos = rst_mem_cpos(RM_PRIVATE);
-		lsm_profile_len = strlen(rendered);
-		lsm = rst_mem_alloc(lsm_profile_len + 1, RM_PRIVATE);
-		if (!lsm) {
+			strncpy(lsm, rendered, lsm_profile_len);
 			xfree(rendered);
-			goto err_nv;
 		}
 
-		strncpy(lsm, rendered, lsm_profile_len);
-		xfree(rendered);
-
 	}
 
 	if (seccomp_filters_get_rst_pos(core, &n_seccomp_filters, &seccomp_filter_pos) < 0)

crtools.c

@@ -41,6 +41,7 @@
 #include "security.h"
 #include "irmap.h"
 #include "fault-injection.h"
+#include "lsm.h"
 
 #include "setproctitle.h"
 
@@ -253,6 +254,7 @@ int main(int argc, char *argv[], char *envp[])
 		{ "freeze-cgroup",		required_argument,	0, 1068 },
 		{ "ghost-limit",		required_argument,	0, 1069 },
 		{ "irmap-scan-path",		required_argument,	0, 1070 },
+		{ "lsm-profile",		required_argument,	0, 1071 },
 		{ },
 	};
 
@@ -498,6 +500,10 @@ int main(int argc, char *argv[], char *envp[])
 			if (irmap_scan_path_add(optarg))
 				return -1;
 			break;
+		case 1071:
+			if (parse_lsm_arg(optarg) < 0)
+				return -1;
+			break;
 		case 'M':
 			{
 				char *aux;

include/cr_options.h

@@ -95,6 +95,8 @@ struct cr_options {
 	bool			overlayfs;
 	size_t			ghost_limit;
 	struct list_head	irmap_scan_paths;
+	bool			lsm_supplied;
+	char			*lsm_profile;
 };
 
 extern struct cr_options opts;

include/lsm.h

@@ -23,7 +23,7 @@ extern int collect_lsm_profile(pid_t, CredsEntry *);
  * Validate that the LSM profiles can be correctly applied (must happen after
  * pstree is set up).
  */
-int validate_lsm(CredsEntry *ce);
+int validate_lsm(char *profile);
 
 /*
  * Render the profile name in the way that the LSM wants it written to
@@ -31,4 +31,5 @@ int validate_lsm(CredsEntry *ce);
  */
 int render_lsm_profile(char *profile, char **val);
 
+extern int parse_lsm_arg(char *arg);
 #endif /* __CR_LSM_H__ */

lsm.c

@@ -7,6 +7,7 @@
 #include "config.h"
 #include "pstree.h"
 #include "util.h"
+#include "cr_options.h"
 
 #include "protobuf.h"
 #include "protobuf/inventory.pb-c.h"
@@ -106,6 +107,14 @@ static int selinux_get_label(pid_t pid, char **output)
 
 void kerndat_lsm(void)
 {
+	/* On restore, if someone passes --lsm-profile, we might end up doing
+	 * detection twice, once during flag parsing and once for
+	 * kerndat_init_rst(). Let's detect when we've already done detection
+	 * and not do it again.
+	 */
+	if (name)
+		return;
+
 	if (access("/sys/kernel/security/apparmor", F_OK) == 0) {
 		get_label = apparmor_get_label;
 		lsmtype = LSMTYPE__APPARMOR;
@@ -156,7 +165,7 @@ int collect_lsm_profile(pid_t pid, CredsEntry *ce)
 // in inventory.c
 extern Lsmtype image_lsm;
 
-int validate_lsm(CredsEntry *ce)
+int validate_lsm(char *lsm_profile)
 {
 	if (image_lsm == LSMTYPE__NO_LSM || image_lsm == lsmtype)
 		return 0;
@@ -166,7 +175,7 @@ int validate_lsm(CredsEntry *ce)
 	 * specified an LSM profile. If not, we won't restore anything anyway,
 	 * so it's fine.
 	 */
-	if (ce->lsm_profile) {
+	if (lsm_profile) {
 		pr_err("mismatched lsm types and lsm profile specified\n");
 		return -1;
 	}
@@ -197,3 +206,44 @@ int render_lsm_profile(char *profile, char **val)
 
 	return 0;
 }
+
+int parse_lsm_arg(char *arg)
+{
+	char *aux;
+
+	kerndat_lsm();
+
+	aux = strchr(arg, ':');
+	if (aux == NULL) {
+		pr_err("invalid argument %s for --lsm-profile", arg);
+		return -1;
+	}
+
+	*aux = '\0';
+	aux++;
+
+	if (strcmp(arg, "apparmor") == 0) {
+		if (lsmtype != LSMTYPE__APPARMOR) {
+			pr_err("apparmor LSM specified but apparmor not supported by kernel\n");
+			return -1;
+		}
+
+		opts.lsm_profile = aux;
+	} else if (strcmp(arg, "selinux") == 0) {
+		if (lsmtype != LSMTYPE__SELINUX) {
+			pr_err("selinux LSM specified but selinux not supported by kernel\n");
+			return -1;
+		}
+
+		opts.lsm_profile = aux;
+	} else if (strcmp(arg, "none") == 0) {
+		opts.lsm_profile = NULL;
+	} else {
+		pr_err("unknown lsm %s\n", arg);
+		return -1;
+	}
+
+	opts.lsm_supplied = true;
+
+	return 0;
+}