selinux: stop passing MAY_NOT_BLOCK to the AVC upon follow_link

commit bda0be7ad9 ("security: make inode_follow_link RCU-walk aware")
switched selinux_inode_follow_link() to use avc_has_perm_flags() and
pass down the MAY_NOT_BLOCK flag if called during RCU walk.  However,
the only test of MAY_NOT_BLOCK occurs during slow_avc_audit()
and only if passing an inode as audit data (LSM_AUDIT_DATA_INODE).  Since
selinux_inode_follow_link() passes a dentry directly, passing MAY_NOT_BLOCK
here serves no purpose.  Switch selinux_inode_follow_link() to use
avc_has_perm() and drop avc_has_perm_flags() since there are no other
users.

Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Paul Moore <paul@paul-moore.com>

security/selinux/avc.c

@@ -867,9 +867,8 @@ static int avc_update_node(struct selinux_avc *avc,
 	 * permissive mode that only appear when in enforcing mode.
 	 *
 	 * See the corresponding handling in slow_avc_audit(), and the
-	 * logic in selinux_inode_follow_link and selinux_inode_permission
-	 * for the VFS MAY_NOT_BLOCK flag, which is transliterated into
-	 * AVC_NONBLOCKING for avc_has_perm_noaudit().
+	 * logic in selinux_inode_permission for the MAY_NOT_BLOCK flag,
+	 * which is transliterated into AVC_NONBLOCKING.
 	 */
 	if (flags & AVC_NONBLOCKING)
 		return 0;
@@ -1209,25 +1208,6 @@ int avc_has_perm(struct selinux_state *state, u32 ssid, u32 tsid, u16 tclass,
 	return rc;
 }
 
-int avc_has_perm_flags(struct selinux_state *state,
-		       u32 ssid, u32 tsid, u16 tclass, u32 requested,
-		       struct common_audit_data *auditdata,
-		       int flags)
-{
-	struct av_decision avd;
-	int rc, rc2;
-
-	rc = avc_has_perm_noaudit(state, ssid, tsid, tclass, requested,
-				  (flags & MAY_NOT_BLOCK) ? AVC_NONBLOCKING : 0,
-				  &avd);
-
-	rc2 = avc_audit(state, ssid, tsid, tclass, requested, &avd, rc,
-			auditdata, flags);
-	if (rc2)
-		return rc2;
-	return rc;
-}
-
 u32 avc_policy_seqno(struct selinux_state *state)
 {
 	return state->avc->avc_cache.latest_notif;

security/selinux/hooks.c

@@ -2925,9 +2925,8 @@ static int selinux_inode_follow_link(struct dentry *dentry, struct inode *inode,
 	if (IS_ERR(isec))
 		return PTR_ERR(isec);
 
-	return avc_has_perm_flags(&selinux_state,
-				  sid, isec->sid, isec->sclass, FILE__READ, &ad,
-				  rcu ? MAY_NOT_BLOCK : 0);
+	return avc_has_perm(&selinux_state,
+			    sid, isec->sid, isec->sclass, FILE__READ, &ad);
 }
 
 static noinline int audit_inode_permission(struct inode *inode,

security/selinux/include/avc.h

@@ -153,11 +153,6 @@ int avc_has_perm(struct selinux_state *state,
 		 u32 ssid, u32 tsid,
 		 u16 tclass, u32 requested,
 		 struct common_audit_data *auditdata);
-int avc_has_perm_flags(struct selinux_state *state,
-		       u32 ssid, u32 tsid,
-		       u16 tclass, u32 requested,
-		       struct common_audit_data *auditdata,
-		       int flags);
 
 int avc_has_extended_perms(struct selinux_state *state,
 			   u32 ssid, u32 tsid, u16 tclass, u32 requested,