[PATCH v3 10/10] acl: don't depend on IOP_XATTR

[Christian Brauner <brauner@kernel.org>]

All codepaths that don't want to implement POSIX ACLs should simply not
implement the associated inode operations instead of relying on
IOP_XATTR. That's the case for all filesystems today.

For vfs_listxattr() all filesystems that explicitly turn of xattrs for a
given inode all set inode->i_op to a dedicated set of inode operations
that doesn't implement ->listxattr().  We can remove the dependency of
vfs_listxattr() on IOP_XATTR.

Removing this dependency will allow us to decouple POSIX ACLs from
IOP_XATTR and they can still be listed even if no other xattr handlers
are implemented. Otherwise we would have to implement elaborate schemes
to raise IOP_XATTR even if sb->s_xattr is set to NULL.

Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
---
Changes in v3:
- Patch introduced.
---
 fs/posix_acl.c | 12 ++++--------
 fs/xattr.c     | 25 ++++++++++++++++++++++++-
 2 files changed, 28 insertions(+), 9 deletions(-)

diff --git a/fs/posix_acl.c b/fs/posix_acl.c
index 7a4d89897c37..881a7fd1cacb 100644
--- a/fs/posix_acl.c
+++ b/fs/posix_acl.c
@@ -1132,12 +1132,10 @@ int vfs_set_acl(struct user_namespace *mnt_userns, struct dentry *dentry,
 	if (error)
 		goto out_inode_unlock;
 
-	if (inode->i_opflags & IOP_XATTR)
+	if (likely(!is_bad_inode(inode)))
 		error = set_posix_acl(mnt_userns, dentry, acl_type, kacl);
-	else if (unlikely(is_bad_inode(inode)))
-		error = -EIO;
 	else
-		error = -EOPNOTSUPP;
+		error = -EIO;
 	if (!error) {
 		fsnotify_xattr(dentry);
 		evm_inode_post_set_acl(dentry, acl_name, kacl);
@@ -1242,12 +1240,10 @@ int vfs_remove_acl(struct user_namespace *mnt_userns, struct dentry *dentry,
 	if (error)
 		goto out_inode_unlock;
 
-	if (inode->i_opflags & IOP_XATTR)
+	if (likely(!is_bad_inode(inode)))
 		error = set_posix_acl(mnt_userns, dentry, acl_type, NULL);
-	else if (unlikely(is_bad_inode(inode)))
-		error = -EIO;
 	else
-		error = -EOPNOTSUPP;
+		error = -EIO;
 	if (!error) {
 		fsnotify_xattr(dentry);
 		evm_inode_post_remove_acl(mnt_userns, dentry, acl_name);
diff --git a/fs/xattr.c b/fs/xattr.c
index 8743402a5e8b..56e37461014e 100644
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -457,6 +457,28 @@ vfs_getxattr(struct user_namespace *mnt_userns, struct dentry *dentry,
 }
 EXPORT_SYMBOL_GPL(vfs_getxattr);
 
+/**
+ * vfs_listxattr - retrieve \0 separated list of xattr names
+ * @dentry: the dentry from whose inode the xattr names are retrieved
+ * @list: buffer to store xattr names into
+ * @size: size of the buffer
+ *
+ * This function returns the names of all xattrs associated with the
+ * inode of @dentry.
+ *
+ * Note, for legacy reasons the vfs_listxattr() function lists POSIX
+ * ACLs as well. Since POSIX ACLs are decoupled from IOP_XATTR the
+ * vfs_listxattr() function doesn't check for this flag since a
+ * filesystem could implement POSIX ACLs without implementing any other
+ * xattrs.
+ *
+ * However, since all codepaths that remove IOP_XATTR also assign of
+ * inode operations that either don't implement or implement a stub
+ * ->listxattr() operation.
+ *
+ * Return: On success, the size of the buffer that was used. On error a
+ *         negative error code.
+ */
 ssize_t
 vfs_listxattr(struct dentry *dentry, char *list, size_t size)
 {
@@ -466,7 +488,8 @@ vfs_listxattr(struct dentry *dentry, char *list, size_t size)
 	error = security_inode_listxattr(dentry);
 	if (error)
 		return error;
-	if (inode->i_op->listxattr && (inode->i_opflags & IOP_XATTR)) {
+
+	if (inode->i_op->listxattr) {
 		error = inode->i_op->listxattr(dentry, list, size);
 	} else {
 		error = security_inode_listsecurity(inode, list, size);

-- 
2.34.1