[PATCH v2 05/12] fs-verity: implement FS_IOC_ENABLE_VERITY ioctl

Eric Biggers
2018-11-01T22:54:22Z

From: Eric Biggers <ebiggers@google.com>

Add a function for filesystems to call to implement the
FS_IOC_ENABLE_VERITY ioctl. This ioctl enables fs-verity on a file,
after userspace has appended verity metadata to it.

This ioctl is documented in Documentation/filesystem/fsverity.rst;
see there for more information.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
fs/verity/Makefile | 2 +-
fs/verity/ioctl.c | 117 +++++++++++++++++++++++++++++++++++++++
include/linux/fsverity.h | 11 ++++
3 files changed, 129 insertions(+), 1 deletion(-)
create mode 100644 fs/verity/ioctl.c

diff --git a/fs/verity/Makefile b/fs/verity/Makefile
index a6c7cefb61ab7..6450925e3a8b7 100644
--- a/fs/verity/Makefile
+++ b/fs/verity/Makefile
@@ -1,3 +1,3 @@
obj-$(CONFIG_FS_VERITY) += fsverity.o

-fsverity-y := hash_algs.o setup.o verify.o
+fsverity-y := hash_algs.o ioctl.o setup.o verify.o
diff --git a/fs/verity/ioctl.c b/fs/verity/ioctl.c
new file mode 100644
index 0000000000000..c5f0022cb3bef
--- /dev/null
+++ b/fs/verity/ioctl.c
@@ -0,0 +1,117 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * fs/verity/ioctl.c: fs-verity ioctls
+ *
+ * Copyright 2018 Google LLC
+ *
+ * Originally written by Jaegeuk Kim and Michael Halcrow;
+ * heavily rewritten by Eric Biggers.
+ */
+
+#include "fsverity_private.h"
+
+#include <linux/mm.h>
+#include <linux/mount.h>
+#include <linux/uaccess.h>
+
+/**
+ * fsverity_ioctl_enable - enable fs-verity on a file
+ *
+ * Enable fs-verity on a file. Verity metadata must have already been appended
+ * to the file. See Documentation/filesystems/fsverity.rst, section
+ * 'FS_IOC_ENABLE_VERITY' for details.
+ *
+ * Return: 0 on success, -errno on failure
+ */
+int fsverity_ioctl_enable(struct file *filp, const void __user *arg)
+{
+ struct inode *inode = file_inode(filp);
+ struct fsverity_info *vi;
+ int err;
+
+ err = inode_permission(inode, MAY_WRITE);
+ if (err)
+ return err;
+
+ if (IS_APPEND(inode))
+ return -EPERM;
+
+ if (arg) /* argument is reserved */
+ return -EINVAL;
+
+ if (S_ISDIR(inode->i_mode))
+ return -EISDIR;
+
+ if (!S_ISREG(inode->i_mode))
+ return -EINVAL;
+
+ err = mnt_want_write_file(filp);
+ if (err)
+ goto out;
+
+ /*
+ * Temporarily lock out writers via writable file descriptors or
+ * truncate(). This should stabilize the contents of the file as well
+ * as its size. Note that at the end of this ioctl we will unlock
+ * writers, but at that point the verity bit will be set (if the ioctl
+ * succeeded), preventing future writers.
+ */
+ err = deny_write_access(filp);
+ if (err) /* -ETXTBSY */
+ goto out_drop_write;
+
+ /*
+ * fsync so that the verity bit can't be persisted to disk prior to the
+ * data, causing verification errors after a crash.
+ */
+ err = vfs_fsync(filp, 1);
+ if (err)
+ goto out_allow_write;
+
+ /* Serialize concurrent use of this ioctl on the same inode */
+ inode_lock(inode);
+
+ if (get_fsverity_info(inode)) { /* fs-verity already enabled? */
+ err = -EEXIST;
+ goto out_unlock;
+ }
+
+ /* Validate the verity metadata */
+ vi = create_fsverity_info(inode, true);
+ if (IS_ERR(vi)) {
+ err = PTR_ERR(vi);
+ if (err == -EINVAL) /* distinguish "invalid metadata" case */
+ err = -EBADMSG;
+ goto out_unlock;
+ }
+
+ /*
+ * Ask the filesystem to mark the file as a verity file, e.g. by setting
+ * the verity bit in the inode.
+ */
+ err = inode->i_sb->s_vop->set_verity(inode, vi->data_i_size);
+ if (err)
+ goto out_free_vi;
+
+ /* Invalidate all cached pages, forcing re-verification */
+ truncate_inode_pages(inode->i_mapping, 0);
+
+ /*
+ * Set ->i_verity_info, unless another task managed to do it already
+ * between ->set_verity() and here.
+ */
+ if (set_fsverity_info(inode, vi))
+ vi = NULL;
+ err = 0;
+out_free_vi:
+ free_fsverity_info(vi);
+out_unlock:
+ inode_unlock(inode);
+out_allow_write:
+ allow_write_access(filp);
+out_drop_write:
+ mnt_drop_write_file(filp);
+out:
+ return err;
+}
+EXPORT_SYMBOL_GPL(fsverity_ioctl_enable);
diff --git a/include/linux/fsverity.h b/include/linux/fsverity.h
index 15478fe7d55aa..5de50b52ccc70 100644
--- a/include/linux/fsverity.h
+++ b/include/linux/fsverity.h
@@ -21,6 +21,9 @@ struct fsverity_operations {

#if __FS_HAS_VERITY

+/* ioctl.c */
+extern int fsverity_ioctl_enable(struct file *filp, const void __user *arg);
+
/* setup.c */
extern int fsverity_file_open(struct inode *inode, struct file *filp);
extern int fsverity_prepare_setattr(struct dentry *dentry, struct iattr *attr);
@@ -40,6 +43,14 @@ static inline bool fsverity_check_hole(struct inode *inode, struct page *page)

#else /* !__FS_HAS_VERITY */

+/* ioctl.c */
+
+static inline int fsverity_ioctl_enable(struct file *filp,
+ const void __user *arg)
+{
+ return -EOPNOTSUPP;
+}
+
/* setup.c */

static inline int fsverity_file_open(struct inode *inode, struct file *filp)
--
2.19.1.568.g152ad8e336-goog