SELINUX: Make selinux cache VFS RCU walks safe

Now that the security modules can decide whether they support the
dcache RCU walk or not it's possible to make selinux a bit more
RCU friendly.  The SELinux AVC and security server access decision
code is RCU safe.  A specific piece of the LSM audit code may not
be RCU safe.

This patch makes the VFS RCU walk retry if it would hit the non RCU
safe chunk of code.  It will normally just work under RCU.  This is
done simply by passing the VFS RCU state as a flag down into the
avc_audit() code and returning ECHILD there if it would have an issue.

Based-on-patch-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Eric Paris <eparis@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 13 insertions, 5 deletions

diff --git a/security/selinux/include/avc.h b/security/selinux/include/avc.h
index 5615081..e77b2ac 100644
--- a/security/selinux/include/avc.h
+++ b/security/selinux/include/avc.h
@@ -54,11 +54,11 @@ struct avc_cache_stats {
 
 void __init avc_init(void);
 
-void avc_audit(u32 ssid, u32 tsid,
+int avc_audit(u32 ssid, u32 tsid,
 	       u16 tclass, u32 requested,
 	       struct av_decision *avd,
 	       int result,
-	       struct common_audit_data *a);
+	      struct common_audit_data *a, unsigned flags);
 
 #define AVC_STRICT 1 /* Ignore permissive mode. */
 int avc_has_perm_noaudit(u32 ssid, u32 tsid,
@@ -66,9 +66,17 @@ int avc_has_perm_noaudit(u32 ssid, u32 tsid,
 			 unsigned flags,
 			 struct av_decision *avd);
 
-int avc_has_perm(u32 ssid, u32 tsid,
-		 u16 tclass, u32 requested,
-		 struct common_audit_data *auditdata);
+int avc_has_perm_flags(u32 ssid, u32 tsid,
+		       u16 tclass, u32 requested,
+		       struct common_audit_data *auditdata,
+		       unsigned);
+
+static inline int avc_has_perm(u32 ssid, u32 tsid,
+			       u16 tclass, u32 requested,
+			       struct common_audit_data *auditdata)
+{
+	return avc_has_perm_flags(ssid, tsid, tclass, requested, auditdata, 0);
+}
 
 u32 avc_policy_seqno(void);