xattr: use posix acl api

In previous patches we built a new posix api solely around get and set
inode operations. Now that we have all the pieces in place we can switch
the system calls and the vfs over to only rely on this api when
interacting with posix acls. This finally removes all type unsafety and
type conversion issues explained in detail in [1] that we aim to get rid
of.

With the new posix acl api we immediately translate into an appropriate
kernel internal struct posix_acl format both when getting and setting
posix acls. This is a stark contrast to before were we hacked unsafe raw
values into the uapi struct that was stored in a void pointer relying
and having filesystems and security modules hack around in the uapi
struct as well.

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, 8 insertions, 2 deletions

diff --git a/include/linux/posix_acl_xattr.h b/include/linux/posix_acl_xattr.h
index bf30296389d7..c5d5fbc348dc 100644
--- a/include/linux/posix_acl_xattr.h
+++ b/include/linux/posix_acl_xattr.h
@@ -33,6 +33,8 @@ posix_acl_xattr_count(size_t size)
 }
 
 #ifdef CONFIG_FS_POSIX_ACL
+struct posix_acl *posix_acl_from_xattr(struct user_namespace *user_ns,
+				       const void *value, size_t size);
 void posix_acl_fix_xattr_from_user(void *value, size_t size);
 void posix_acl_fix_xattr_to_user(void *value, size_t size);
 void posix_acl_getxattr_idmapped_mnt(struct user_namespace *mnt_userns,
@@ -42,6 +44,12 @@ ssize_t vfs_posix_acl_to_xattr(struct user_namespace *mnt_userns,
 			       struct inode *inode, const struct posix_acl *acl,
 			       void *buffer, size_t size);
 #else
+static inline struct posix_acl *
+posix_acl_from_xattr(struct user_namespace *user_ns, const void *value,
+		     size_t size)
+{
+	return ERR_PTR(-EOPNOTSUPP);
+}
 static inline void posix_acl_fix_xattr_from_user(void *value, size_t size)
 {
 }
@@ -63,8 +71,6 @@ static inline ssize_t vfs_posix_acl_to_xattr(struct user_namespace *mnt_userns,
 }
 #endif
 
-struct posix_acl *posix_acl_from_xattr(struct user_namespace *user_ns, 
-				       const void *value, size_t size);
 int posix_acl_to_xattr(struct user_namespace *user_ns,
 		       const struct posix_acl *acl, void *buffer, size_t size);
 struct posix_acl *vfs_set_acl_prepare(struct user_namespace *mnt_userns,