aufs: bugfix, support for selinux

SELinux's d_instantiate hook calls __vfs_getxattr() BEFORE d_inode is
set.  Aufs should not rely upon d_inode and should use the parameter
inode instead.
Reported-by: "jon bird" <news@onasticksoftware.co.uk>
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>
(cherry picked from commit 5777718fd657e1cfdf006cd16b524c65cf2fe09b)

fs/aufs/i_op.c

@@ -1170,15 +1170,14 @@ static void au_refresh_iattr(struct inode *inode, struct kstat *st,
  * returns zero or negative (an error).
  * @dentry will be read-locked in success.
  */
-int au_h_path_getattr(struct dentry *dentry, int force, struct path *h_path,
-		      int locked)
+int au_h_path_getattr(struct dentry *dentry, struct inode *inode, int force,
+		      struct path *h_path, int locked)
 {
 	int err;
 	unsigned int mnt_flags, sigen;
 	unsigned char udba_none;
 	aufs_bindex_t bindex;
 	struct super_block *sb, *h_sb;
-	struct inode *inode;
 
 	h_path->mnt = NULL;
 	h_path->dentry = NULL;
@@ -1219,7 +1218,11 @@ int au_h_path_getattr(struct dentry *dentry, int force, struct path *h_path,
 		di_read_lock_child(dentry, AuLock_IR);
 
 body:
+	if (!inode) {
 		inode = d_inode(dentry);
+		if (unlikely(!inode))
+			goto out;
+	}
 	bindex = au_ibtop(inode);
 	h_path->mnt = au_sbr_mnt(sb, bindex);
 	h_sb = h_path->mnt->mnt_sb;
@@ -1259,7 +1262,8 @@ static int aufs_getattr(const struct path *path, struct kstat *st,
 	err = si_read_lock(sb, AuLock_FLUSH | AuLock_NOPLM);
 	if (unlikely(err))
 		goto out;
-	err = au_h_path_getattr(dentry, /*force*/0, &h_path, /*locked*/0);
+	err = au_h_path_getattr(dentry, /*inode*/NULL, /*force*/0, &h_path,
+				/*locked*/0);
 	if (unlikely(err))
 		goto out_si;
 	if (unlikely(!h_path.dentry))

fs/aufs/inode.h

@@ -194,8 +194,8 @@ struct au_icpup_args {
 int au_pin_and_icpup(struct dentry *dentry, struct iattr *ia,
 		     struct au_icpup_args *a);
 
-int au_h_path_getattr(struct dentry *dentry, int force, struct path *h_path,
-		      int locked);
+int au_h_path_getattr(struct dentry *dentry, struct inode *inode, int force,
+		      struct path *h_path, int locked);
 
 /* i_op_add.c */
 int au_may_add(struct dentry *dentry, aufs_bindex_t bindex,

fs/aufs/xattr.c

@@ -181,7 +181,7 @@ out:
 
 static int au_smack_reentering(struct super_block *sb)
 {
-#if IS_ENABLED(CONFIG_SECURITY_SMACK)
+#if IS_ENABLED(CONFIG_SECURITY_SMACK) || IS_ENABLED(CONFIG_SECURITY_SELINUX)
 	/*
 	 * as a part of lookup, smack_d_instantiate() is called, and it calls
 	 * i_op->getxattr(). ouch.
@@ -212,7 +212,8 @@ struct au_lgxattr {
 	} u;
 };
 
-static ssize_t au_lgxattr(struct dentry *dentry, struct au_lgxattr *arg)
+static ssize_t au_lgxattr(struct dentry *dentry, struct inode *inode,
+			  struct au_lgxattr *arg)
 {
 	ssize_t err;
 	int reenter;
@@ -226,7 +227,7 @@ static ssize_t au_lgxattr(struct dentry *dentry, struct au_lgxattr *arg)
 		if (unlikely(err))
 			goto out;
 	}
-	err = au_h_path_getattr(dentry, /*force*/1, &h_path, reenter);
+	err = au_h_path_getattr(dentry, inode, /*force*/1, &h_path, reenter);
 	if (unlikely(err))
 		goto out_si;
 	if (unlikely(!h_path.dentry))
@@ -268,11 +269,10 @@ ssize_t aufs_listxattr(struct dentry *dentry, char *list, size_t size)
 		},
 	};
 
-	return au_lgxattr(dentry, &arg);
+	return au_lgxattr(dentry, /*inode*/NULL, &arg);
 }
 
-static ssize_t au_getxattr(struct dentry *dentry,
-			   struct inode *inode __maybe_unused,
+static ssize_t au_getxattr(struct dentry *dentry, struct inode *inode,
 			   const char *name, void *value, size_t size)
 {
 	struct au_lgxattr arg = {
@@ -284,7 +284,7 @@ static ssize_t au_getxattr(struct dentry *dentry,
 		},
 	};
 
-	return au_lgxattr(dentry, &arg);
+	return au_lgxattr(dentry, inode, &arg);
 }
 
 static int au_setxattr(struct dentry *dentry, struct inode *inode,