fs-verity: implement FS_IOC_MEASURE_VERITY ioctl

Add a function for filesystems to call to implement the
FS_IOC_MEASURE_VERITY ioctl.  This ioctl retrieves the file measurement
that fs-verity calculated for the given file and is enforcing for reads;
i.e., reads that don't match this hash will fail.  This ioctl can be
used for authentication or logging of file measurements in userspace.

See the "FS_IOC_MEASURE_VERITY" section of
Documentation/filesystems/fsverity.rst for the documentation.

Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/include/linux/fsverity.h b/include/linux/fsverity.h
index d1a5dbf450c4..3b6b8ccebe7d 100644
--- a/include/linux/fsverity.h
+++ b/include/linux/fsverity.h
@@ -118,6 +118,10 @@ static inline struct fsverity_info *fsverity_get_info(const struct inode *inode)
 
 extern int fsverity_ioctl_enable(struct file *filp, const void __user *arg);
 
+/* measure.c */
+
+extern int fsverity_ioctl_measure(struct file *filp, void __user *arg);
+
 /* open.c */
 
 extern int fsverity_file_open(struct inode *inode, struct file *filp);
@@ -145,6 +149,13 @@ static inline int fsverity_ioctl_enable(struct file *filp,
 	return -EOPNOTSUPP;
 }
 
+/* measure.c */
+
+static inline int fsverity_ioctl_measure(struct file *filp, void __user *arg)
+{
+	return -EOPNOTSUPP;
+}
+
 /* open.c */
 
 static inline int fsverity_file_open(struct inode *inode, struct file *filp)