ovl: implement get acl method

The current way of setting and getting posix acls through the generic
xattr interface is error prone and type unsafe. The vfs needs to
interpret and fixup posix acls before storing or reporting it to
userspace. Various hacks exist to make this work. The code is hard to
understand and difficult to maintain in it's current form. Instead of
making this work by hacking posix acls through xattr handlers we are
building a dedicated posix acl api around the get and set inode
operations. This removes a lot of hackiness and makes the codepaths
easier to maintain. A lot of background can be found in [1].

In order to build a type safe posix api around get and set acl we need
all filesystem to implement get and set acl.

Now that we have added get and set acl inode operations that allow easy
access to the dentry we give overlayfs it's own get and set acl inode
operations.

Since overlayfs is a stacking filesystem it will use the newly added
posix acl api when retrieving posix acls from the relevant layer.

Since overlayfs can also be mounted on top of idmapped layers. If
idmapped layers are used overlayfs must take the layer's idmapping into
account after it retrieved the posix acls from the relevant layer.

Note, until the vfs has been switched to the new posix acl api this
patch is a non-functional change.

Link: https://lore.kernel.org/all/20220801145520.1532837-1-brauner@kernel.org [1]
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>

1 files changed, 15 insertions, 2 deletions

diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index eee8f08d32b6..d334977030c8 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -594,9 +594,22 @@ int ovl_xattr_get(struct dentry *dentry, struct inode *inode, const char *name,
 ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size);
 
 #ifdef CONFIG_FS_POSIX_ACL
-struct posix_acl *ovl_get_acl(struct inode *inode, int type, bool rcu);
+struct posix_acl *do_ovl_get_acl(struct user_namespace *mnt_userns,
+				 struct inode *inode, int type,
+				 bool rcu, bool noperm);
+static inline struct posix_acl *ovl_get_inode_acl(struct inode *inode, int type,
+						  bool rcu)
+{
+	return do_ovl_get_acl(&init_user_ns, inode, type, rcu, true);
+}
+static inline struct posix_acl *ovl_get_acl(struct user_namespace *mnt_userns,
+					    struct dentry *dentry, int type)
+{
+	return do_ovl_get_acl(mnt_userns, d_inode(dentry), type, false, false);
+}
 #else
-#define ovl_get_acl	NULL
+#define ovl_get_inode_acl	NULL
+#define ovl_get_acl		NULL
 #endif
 
 int ovl_update_time(struct inode *inode, struct timespec64 *ts, int flags);