[PATCH v2] libsemanage: set selinux policy root around calls to selinux_boolean_sub

[Stephen Smalley <sds@tycho.nsa.gov>]

As reported in #109, semodule -p /path/to/policyroot -s minimum -n -B
tries to use /etc/selinux/targeted/booleans.subs_dist.  This is because
it invokes the libselinux selinux_boolean_sub() interface, which uses
the active/installed policy files rather than the libsemanage ones.

Switch the selinux policy root around the selinux_boolean_sub() call
to incorporate the semanage root as a prefix and to use the specified
policy store as a suffix so that the correct booleans.subs_dist file
(if any) is used.

The underlying bug is that booleans.subs_dist is not itself managed
via libsemanage. If it was managed and therefore lived within the
policy store, then libsemanage could access the appropriate
booleans.subs_dist file without using the libselinux interface at all,
and thus would not need to modify the selinux policy root.  Moving
booleans.subs_dist to a managed file is deferred to a future change.

Test:
dnf install selinux-policy-minimum selinux-policy-targeted
cd / && tar cf - etc/selinux var/lib/selinux | (cd ~/policy-root; tar xvpf -)
strace semodule -p ~/policy-root -s minimum -n -B

Before:
openat(AT_FDCWD, "/etc/selinux/targeted/booleans.subs_dist", O_RDONLY|O_CLOEXEC) = 5

After:
openat(AT_FDCWD, "/home/sds/policy-root/etc/selinux/minimum/booleans.subs_dist", O_RDONLY|O_CLOEXEC) = 5

Fixes https://github.com/SELinuxProject/selinux/issues/109

Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
---
v2 skips setting of the policy root if they already match, introduces a
hidden prototype and definition for internal callers of semanage_root(),
and tests that selinux_policy_root() is non-NULL before strdup'ing it.
 libsemanage/src/boolean_record.c  | 54 +++++++++++++++++++++++++++++--
 libsemanage/src/handle.c          |  2 ++
 libsemanage/src/handle_internal.h |  9 +++---
 3 files changed, 59 insertions(+), 6 deletions(-)

diff --git a/libsemanage/src/boolean_record.c b/libsemanage/src/boolean_record.c
index 665c0223..c234094e 100644
--- a/libsemanage/src/boolean_record.c
+++ b/libsemanage/src/boolean_record.c
@@ -6,7 +6,9 @@
  * Implements: record_key_t (Database Record Key)
  */
 
+#include <string.h>
 #include <sepol/boolean_record.h>
+#include "handle_internal.h"
 
 typedef sepol_bool_t semanage_bool_t;
 typedef sepol_bool_key_t semanage_bool_key_t;
@@ -84,10 +86,58 @@ hidden_def(semanage_bool_get_name)
 int semanage_bool_set_name(semanage_handle_t * handle,
 			   semanage_bool_t * boolean, const char *name)
 {
-	int rc;
-	char *subname = selinux_boolean_sub(name);
+	int rc = -1;
+	const char *prefix = semanage_root();
+	const char *storename = handle->conf->store_path;
+	const char *selinux_root = selinux_policy_root();
+	char *oldroot;
+	char *olddir;
+	char *subname = NULL;
+	char *newroot = NULL;
+	char *end;
+
+	if (!selinux_root)
+		return -1;
+
+	oldroot = strdup(selinux_root);
+	if (!oldroot)
+		return -1;
+	olddir = strdup(oldroot);
+	if (!olddir)
+		goto out;
+	end = strrchr(olddir, '/');
+	if (!end)
+		goto out;
+	end++;
+	*end = '\0';
+	rc = asprintf(&newroot, "%s%s%s", prefix, olddir, storename);
+	if (rc < 0)
+		goto out;
+
+	if (strcmp(oldroot, newroot)) {
+		rc = selinux_set_policy_root(newroot);
+		if (rc)
+			goto out;
+	}
+
+	subname = selinux_boolean_sub(name);
+	if (!subname) {
+		rc = -1;
+		goto out;
+	}
+
+	if (strcmp(oldroot, newroot)) {
+		rc = selinux_set_policy_root(oldroot);
+		if (rc)
+			goto out;
+	}
+
 	rc = sepol_bool_set_name(handle->sepolh, boolean, subname);
+out:
 	free(subname);
+	free(oldroot);
+	free(olddir);
+	free(newroot);
 	return rc;
 }
 
diff --git a/libsemanage/src/handle.c b/libsemanage/src/handle.c
index a6567bd4..e5109aef 100644
--- a/libsemanage/src/handle.c
+++ b/libsemanage/src/handle.c
@@ -58,6 +58,8 @@ const char * semanage_root(void)
 	return private_semanage_root;
 }
 
+hidden_def(semanage_root);
+
 semanage_handle_t *semanage_handle_create(void)
 {
 	semanage_handle_t *sh = NULL;
diff --git a/libsemanage/src/handle_internal.h b/libsemanage/src/handle_internal.h
index 66ce2708..d4b4d9c7 100644
--- a/libsemanage/src/handle_internal.h
+++ b/libsemanage/src/handle_internal.h
@@ -5,8 +5,9 @@
 #include "dso.h"
 
 hidden_proto(semanage_begin_transaction)
-    hidden_proto(semanage_handle_destroy)
-    hidden_proto(semanage_reload_policy)
-    hidden_proto(semanage_access_check)
-    hidden_proto(semanage_set_root)
+hidden_proto(semanage_handle_destroy)
+hidden_proto(semanage_reload_policy)
+hidden_proto(semanage_access_check)
+hidden_proto(semanage_set_root)
+hidden_proto(semanage_root)
 #endif
-- 
2.20.1