libselinux: lazy init

Revive Steve Grubb's patch for libselinux lazy init and extend it to
address not only the reading of /etc/selinux/config but also probing
for /selinux/class and reading of /selinux/mls.  This should reduce the
need for dontaudit rules for programs that link with libselinux and it
should reduce unnecessary overhead.

I did not convert init_selinuxmnt over to lazy init since the functions
that use selinux_mnt are not localized, and it only requires stat'ing
of /selinux in the common case.

I couldn't see a valid reason why we needed fini_obj_class_compat(), as
the existence of /selinux/class will only change across a reboot with
different kernel versions.  fini_context_translations() already had a
comment saying that it was unnecessary as well.

Before:
$ strace ls 2> err
$ grep selinux err
open("/lib/libselinux.so.1", O_RDONLY)  = 3
open("/etc/selinux/config", O_RDONLY|O_LARGEFILE) = 3
statfs64("/selinux", 84, {f_type=0xf97cff8c, f_bsize=4096, f_blocks=0, f_bfree=0, f_bavail=0, f_files=0, f_ffree=0, f_fsid={0, 0}, f_namelen=255, f_frsize=4096}) = 0
stat64("/selinux/class", {st_mode=S_IFDIR|0555, st_size=0, ...}) = 0
open("/selinux/mls", O_RDONLY|O_LARGEFILE) = 3

After:
$ strace ls 2> err
$ grep selinux err
open("/lib/libselinux.so.1", O_RDONLY)  = 3
statfs64("/selinux", 84, {f_type=0xf97cff8c, f_bsize=4096, f_blocks=0, f_bfree=0, f_bavail=0, f_files=0, f_ffree=0, f_fsid={0, 0}, f_namelen=255, f_frsize=4096}) = 0

Original-patch-by:  Steve Grubb <linux_4ever@yahoo.com>
Signed-off-by:  Stephen Smalley <sds@tycho.nsa.gov>

1 files changed, 27 insertions, 1 deletions

diff --git a/libselinux/src/stringrep.c b/libselinux/src/stringrep.c
index b3f3120e..b19bce73 100644
--- a/libselinux/src/stringrep.c
+++ b/libselinux/src/stringrep.c
@@ -152,7 +152,25 @@ static const struct av_inherit {
 #define NVECTORS ARRAY_SIZE(av_perm_to_string)
 #define MAXVECTORS 8*sizeof(access_vector_t)
 
-extern int obj_class_compat;
+static pthread_once_t once = PTHREAD_ONCE_INIT;
+
+static int obj_class_compat;
+
+static void init_obj_class_compat(void)
+{
+	char path[PATH_MAX];
+	struct stat s;
+
+	if (!selinux_mnt)
+		return;
+
+	snprintf(path,PATH_MAX,"%s/class",selinux_mnt);
+	if (stat(path,&s) < 0)
+		return;
+
+	if (S_ISDIR(s.st_mode))
+		obj_class_compat = 0;
+}
 
 struct discover_class_node {
 	char *name;
@@ -420,6 +438,8 @@ security_class_t string_to_security_class(const char *s)
 {
 	struct discover_class_node *node;
 
+	__selinux_once(once, init_obj_class_compat);
+
 	if (obj_class_compat)
 		return string_to_security_class_compat(s);
 
@@ -441,6 +461,8 @@ access_vector_t string_to_av_perm(security_class_t tclass, const char *s)
 	struct discover_class_node *node;
 	security_class_t kclass = unmap_class(tclass);
 
+	__selinux_once(once, init_obj_class_compat);
+
 	if (obj_class_compat)
 		return map_perm(tclass, string_to_av_perm_compat(kclass, s));
 
@@ -462,6 +484,8 @@ const char *security_class_to_string(security_class_t tclass)
 
 	tclass = unmap_class(tclass);
 
+	__selinux_once(once, init_obj_class_compat);
+
 	if (obj_class_compat)
 		return security_class_to_string_compat(tclass);
 
@@ -481,6 +505,8 @@ const char *security_av_perm_to_string(security_class_t tclass,
 	av = unmap_perm(tclass, av);
 	tclass = unmap_class(tclass);
 
+	__selinux_once(once, init_obj_class_compat);
+
 	if (obj_class_compat)
 		return security_av_perm_to_string_compat(tclass,av);