ovl: fix xattr get and set with selinux

inode_doinit_with_dentry() in SELinux wants to read the upper inode's xattr
to get security label, and ovl_xattr_get() calls ovl_dentry_real(), which
depends on dentry->d_inode, but d_inode is null and not initialized yet at
this point resulting in an Oops.

Fix by getting the upperdentry info from the inode directly in this case.
Reported-by: NEryu Guan <eguan@redhat.com>
Fixes: 09d8b586 ("ovl: move __upperdentry to ovl_inode")
Signed-off-by: NMiklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/inode.c

@@ -202,37 +202,38 @@ bool ovl_is_private_xattr(const char *name)
 		       sizeof(OVL_XATTR_PREFIX) - 1) == 0;
 }
 
-int ovl_xattr_set(struct dentry *dentry, const char *name, const void *value,
-		  size_t size, int flags)
+int ovl_xattr_set(struct dentry *dentry, struct inode *inode, const char *name,
+		  const void *value, size_t size, int flags)
 {
 	int err;
-	struct path realpath;
-	enum ovl_path_type type = ovl_path_real(dentry, &realpath);
+	struct dentry *upperdentry = ovl_i_dentry_upper(inode);
+	struct dentry *realdentry = upperdentry ?: ovl_dentry_lower(dentry);
 	const struct cred *old_cred;
 
 	err = ovl_want_write(dentry);
 	if (err)
 		goto out;
 
-	if (!value && !OVL_TYPE_UPPER(type)) {
-		err = vfs_getxattr(realpath.dentry, name, NULL, 0);
+	if (!value && !upperdentry) {
+		err = vfs_getxattr(realdentry, name, NULL, 0);
 		if (err < 0)
 			goto out_drop_write;
 	}
 
-	err = ovl_copy_up(dentry);
-	if (err)
-		goto out_drop_write;
+	if (!upperdentry) {
+		err = ovl_copy_up(dentry);
+		if (err)
+			goto out_drop_write;
 
-	if (!OVL_TYPE_UPPER(type))
-		ovl_path_upper(dentry, &realpath);
+		realdentry = ovl_dentry_upper(dentry);
+	}
 
 	old_cred = ovl_override_creds(dentry->d_sb);
 	if (value)
-		err = vfs_setxattr(realpath.dentry, name, value, size, flags);
+		err = vfs_setxattr(realdentry, name, value, size, flags);
 	else {
 		WARN_ON(flags != XATTR_REPLACE);
-		err = vfs_removexattr(realpath.dentry, name);
+		err = vfs_removexattr(realdentry, name);
 	}
 	revert_creds(old_cred);
 
@@ -242,12 +243,13 @@ int ovl_xattr_set(struct dentry *dentry, const char *name, const void *value,
 	return err;
 }
 
-int ovl_xattr_get(struct dentry *dentry, const char *name,
+int ovl_xattr_get(struct dentry *dentry, struct inode *inode, const char *name,
 		  void *value, size_t size)
 {
-	struct dentry *realdentry = ovl_dentry_real(dentry);
 	ssize_t res;
 	const struct cred *old_cred;
+	struct dentry *realdentry =
+		ovl_i_dentry_upper(inode) ?: ovl_dentry_lower(dentry);
 
 	old_cred = ovl_override_creds(dentry->d_sb);
 	res = vfs_getxattr(realdentry, name, value, size);

fs/overlayfs/overlayfs.h

@@ -200,6 +200,7 @@ enum ovl_path_type ovl_path_real(struct dentry *dentry, struct path *path);
 struct dentry *ovl_dentry_upper(struct dentry *dentry);
 struct dentry *ovl_dentry_lower(struct dentry *dentry);
 struct dentry *ovl_dentry_real(struct dentry *dentry);
+struct dentry *ovl_i_dentry_upper(struct inode *inode);
 struct inode *ovl_inode_upper(struct inode *inode);
 struct inode *ovl_inode_lower(struct inode *inode);
 struct inode *ovl_inode_real(struct inode *inode);
@@ -271,9 +272,9 @@ int ovl_setattr(struct dentry *dentry, struct iattr *attr);
 int ovl_getattr(const struct path *path, struct kstat *stat,
 		u32 request_mask, unsigned int flags);
 int ovl_permission(struct inode *inode, int mask);
-int ovl_xattr_set(struct dentry *dentry, const char *name, const void *value,
-		  size_t size, int flags);
-int ovl_xattr_get(struct dentry *dentry, const char *name,
+int ovl_xattr_set(struct dentry *dentry, struct inode *inode, const char *name,
+		  const void *value, size_t size, int flags);
+int ovl_xattr_get(struct dentry *dentry, struct inode *inode, const char *name,
 		  void *value, size_t size);
 ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size);
 struct posix_acl *ovl_get_acl(struct inode *inode, int type);

fs/overlayfs/super.c

@@ -692,7 +692,7 @@ ovl_posix_acl_xattr_get(const struct xattr_handler *handler,
 			struct dentry *dentry, struct inode *inode,
 			const char *name, void *buffer, size_t size)
 {
-	return ovl_xattr_get(dentry, handler->name, buffer, size);
+	return ovl_xattr_get(dentry, inode, handler->name, buffer, size);
 }
 
 static int __maybe_unused
@@ -742,7 +742,7 @@ ovl_posix_acl_xattr_set(const struct xattr_handler *handler,
 			return err;
 	}
 
-	err = ovl_xattr_set(dentry, handler->name, value, size, flags);
+	err = ovl_xattr_set(dentry, inode, handler->name, value, size, flags);
 	if (!err)
 		ovl_copyattr(ovl_inode_real(inode), inode);
 
@@ -772,7 +772,7 @@ static int ovl_other_xattr_get(const struct xattr_handler *handler,
 			       struct dentry *dentry, struct inode *inode,
 			       const char *name, void *buffer, size_t size)
 {
-	return ovl_xattr_get(dentry, name, buffer, size);
+	return ovl_xattr_get(dentry, inode, name, buffer, size);
 }
 
 static int ovl_other_xattr_set(const struct xattr_handler *handler,
@@ -780,7 +780,7 @@ static int ovl_other_xattr_set(const struct xattr_handler *handler,
 			       const char *name, const void *value,
 			       size_t size, int flags)
 {
-	return ovl_xattr_set(dentry, name, value, size, flags);
+	return ovl_xattr_set(dentry, inode, name, value, size, flags);
 }
 
 static const struct xattr_handler __maybe_unused

fs/overlayfs/util.c

@@ -157,9 +157,14 @@ struct dentry *ovl_dentry_real(struct dentry *dentry)
 	return ovl_dentry_upper(dentry) ?: ovl_dentry_lower(dentry);
 }
 
+struct dentry *ovl_i_dentry_upper(struct inode *inode)
+{
+	return ovl_upperdentry_dereference(OVL_I(inode));
+}
+
 struct inode *ovl_inode_upper(struct inode *inode)
 {
-	struct dentry *upperdentry = ovl_upperdentry_dereference(OVL_I(inode));
+	struct dentry *upperdentry = ovl_i_dentry_upper(inode);
 
 	return upperdentry ? d_inode(upperdentry) : NULL;
 }