[PATCH v2 19/25] fs: add vfs_remove_fscaps()

[Seth Forshee (DigitalOcean)]

Provide a type-safe interface for removing filesystem capabilities and a
generic implementation suitable for most filesystems. Also add an
internal interface, vfs_remove_fscaps_nosec(), which is called with the
inode lock held and skips security checks for later use from the
capability code.

Signed-off-by: Seth Forshee (DigitalOcean) <sforshee at kernel.org>
---
 fs/xattr.c         | 81 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/fs.h |  2 ++
 2 files changed, 83 insertions(+)

diff --git a/fs/xattr.c b/fs/xattr.c
index 96de43928a51..8b0f7384cbc9 100644
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -324,6 +324,87 @@ int vfs_set_fscaps(struct mnt_idmap *idmap, struct dentry *dentry,
 }
 EXPORT_SYMBOL(vfs_set_fscaps);
 
+static int generic_remove_fscaps(struct mnt_idmap *idmap, struct dentry *dentry)
+{
+	return __vfs_removexattr(idmap, dentry, XATTR_NAME_CAPS);
+}
+
+/**
+ * vfs_remove_fscaps_nosec - remove filesystem capabilities without
+ *                           security checks
+ * @idmap: idmap of the mount the inode was found from
+ * @dentry: the dentry from which to remove filesystem capabilities
+ *
+ * This function removes any filesystem capabilities from the specified
+ * dentry. Does not perform any security checks, and callers must hold the
+ * inode lock.
+ *
+ * Return: 0 on success, a negative errno on error.
+ */
+int vfs_remove_fscaps_nosec(struct mnt_idmap *idmap, struct dentry *dentry)
+{
+	struct inode *inode = dentry->d_inode;
+	int error;
+
+	if (inode->i_op->set_fscaps)
+		error =  inode->i_op->set_fscaps(idmap, dentry, NULL,
+						 XATTR_REPLACE);
+	else
+		error = generic_remove_fscaps(idmap, dentry);
+
+	return error;
+}
+
+/**
+ * vfs_remove_fscaps - remove filesystem capabilities
+ * @idmap: idmap of the mount the inode was found from
+ * @dentry: the dentry from which to remove filesystem capabilities
+ *
+ * This function removes any filesystem capabilities from the specified
+ * dentry.
+ *
+ * Return: 0 on success, a negative errno on error.
+ */
+int vfs_remove_fscaps(struct mnt_idmap *idmap, struct dentry *dentry)
+{
+	struct inode *inode = dentry->d_inode;
+	struct inode *delegated_inode = NULL;
+	int error;
+
+retry_deleg:
+	inode_lock(inode);
+
+	error = xattr_permission(idmap, inode, XATTR_NAME_CAPS, MAY_WRITE);
+	if (error)
+		goto out_inode_unlock;
+
+	error = security_inode_remove_fscaps(idmap, dentry);
+	if (error)
+		goto out_inode_unlock;
+
+	error = try_break_deleg(inode, &delegated_inode);
+	if (error)
+		goto out_inode_unlock;
+
+	error = vfs_remove_fscaps_nosec(idmap, dentry);
+	if (!error) {
+		fsnotify_xattr(dentry);
+		evm_inode_post_remove_fscaps(dentry);
+	}
+
+out_inode_unlock:
+	inode_unlock(inode);
+
+	if (delegated_inode) {
+		error = break_deleg_wait(&delegated_inode);
+		if (!error)
+			goto retry_deleg;
+	}
+
+	return error;
+}
+EXPORT_SYMBOL(vfs_remove_fscaps);
+
 int
 __vfs_setxattr(struct mnt_idmap *idmap, struct dentry *dentry,
 	       struct inode *inode, const char *name, const void *value,
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 4f5d7ed44644..c07427d2fc71 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2122,6 +2122,8 @@ extern int vfs_get_fscaps(struct mnt_idmap *idmap, struct dentry *dentry,
 			  struct vfs_caps *caps);
 extern int vfs_set_fscaps(struct mnt_idmap *idmap, struct dentry *dentry,
 			  const struct vfs_caps *caps, int setxattr_flags);
+extern int vfs_remove_fscaps_nosec(struct mnt_idmap *idmap, struct dentry *dentry);
+extern int vfs_remove_fscaps(struct mnt_idmap *idmap, struct dentry *dentry);
 
 /**
  * enum freeze_holder - holder of the freeze

-- 
2.43.0