[PATCH 1/2] [lsm] introduce a new hook to query LSM for functionality

[Olga Kornievskaia <olga.kornievskaia@gmail.com>]

From: Olga Kornievskaia <kolga@netapp.com>

Add a new hook func_query_vfs to query an LSM module (such as
SELinux) with the intention of finding whether or not it is enabled
or perhaps supports some functionality.

NFS stores security labels for file system objects and SElinux
or any other LSM module can query those objects. But it's
wasteful to do so when no security enforcement is taking place.
Using a new API call of security_func_query_vfs() and asking if

Suggested-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
---
 include/linux/lsm_hook_defs.h | 1 +
 include/linux/security.h      | 4 ++++
 security/security.c           | 6 ++++++
 security/selinux/hooks.c      | 7 +++++++
 4 files changed, 18 insertions(+)

diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index 32a940117e7a..df3454a1fcac 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -257,6 +257,7 @@ LSM_HOOK(int, 0, inode_notifysecctx, struct inode *inode, void *ctx, u32 ctxlen)
 LSM_HOOK(int, 0, inode_setsecctx, struct dentry *dentry, void *ctx, u32 ctxlen)
 LSM_HOOK(int, 0, inode_getsecctx, struct inode *inode, void **ctx,
 	 u32 *ctxlen)
+LSM_HOOK(int, 0, func_query_vfs, unsigned int)
 
 #if defined(CONFIG_SECURITY) && defined(CONFIG_WATCH_QUEUE)
 LSM_HOOK(int, 0, post_notification, const struct cred *w_cred,
diff --git a/include/linux/security.h b/include/linux/security.h
index bc2725491560..e15964059fa4 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -456,6 +456,10 @@ int security_inode_notifysecctx(struct inode *inode, void *ctx, u32 ctxlen);
 int security_inode_setsecctx(struct dentry *dentry, void *ctx, u32 ctxlen);
 int security_inode_getsecctx(struct inode *inode, void **ctx, u32 *ctxlen);
 int security_locked_down(enum lockdown_reason what);
+#define LSM_FQUERY_VFS_NONE     0x00000000
+#define LSM_FQUERY_VFS_XATTRS   0x00000001
+int security_func_query_vfs(unsigned int flags);
+
 #else /* CONFIG_SECURITY */
 
 static inline int call_blocking_lsm_notifier(enum lsm_event event, void *data)
diff --git a/security/security.c b/security/security.c
index a28045dc9e7f..502b33865238 100644
--- a/security/security.c
+++ b/security/security.c
@@ -2067,6 +2067,12 @@ int security_inode_getsecctx(struct inode *inode, void **ctx, u32 *ctxlen)
 }
 EXPORT_SYMBOL(security_inode_getsecctx);
 
+int security_func_query_vfs(unsigned int flags)
+{
+	return call_int_hook(func_query_vfs, 0, flags);
+}
+EXPORT_SYMBOL(security_func_query_vfs);
+
 #ifdef CONFIG_WATCH_QUEUE
 int security_post_notification(const struct cred *w_cred,
 			       const struct cred *cred,
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 6b1826fc3658..38f47570e214 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -92,6 +92,7 @@
 #include <uapi/linux/mount.h>
 #include <linux/fsnotify.h>
 #include <linux/fanotify.h>
+#include <linux/security.h>
 
 #include "avc.h"
 #include "objsec.h"
@@ -6502,6 +6503,11 @@ static void selinux_inode_invalidate_secctx(struct inode *inode)
 	spin_unlock(&isec->lock);
 }
 
+static int selinux_func_query_vfs(unsigned int flags)
+{
+	return !!(flags & LSM_FQUERY_VFS_XATTRS);
+}
+
 /*
  *	called with inode->i_mutex locked
  */
@@ -7085,6 +7091,7 @@ static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
 	LSM_HOOK_INIT(inode_invalidate_secctx, selinux_inode_invalidate_secctx),
 	LSM_HOOK_INIT(inode_notifysecctx, selinux_inode_notifysecctx),
 	LSM_HOOK_INIT(inode_setsecctx, selinux_inode_setsecctx),
+	LSM_HOOK_INIT(func_query_vfs, selinux_func_query_vfs),
 
 	LSM_HOOK_INIT(unix_stream_connect, selinux_socket_unix_stream_connect),
 	LSM_HOOK_INIT(unix_may_send, selinux_socket_unix_may_send),
-- 
2.18.2