From: Eric Biggers <ebiggers@xxxxxxxxxx>
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@xxxxxxx>
Reviewed-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
---
fs/verity/Makefile | 1 +
fs/verity/measure.c | 57 ++++++++++++++++++++++++++++++++++++++++
include/linux/fsverity.h | 11 ++++++++
3 files changed, 69 insertions(+)
create mode 100644 fs/verity/measure.c
diff --git a/fs/verity/Makefile b/fs/verity/Makefile
index 04b37475fd280..6f7675ae0a311 100644
--- a/fs/verity/Makefile
+++ b/fs/verity/Makefile
@@ -3,5 +3,6 @@
obj-$(CONFIG_FS_VERITY) += enable.o \
hash_algs.o \
init.o \
+ measure.o \
open.o \
verify.o
diff --git a/fs/verity/measure.c b/fs/verity/measure.c
new file mode 100644
index 0000000000000..05049b68c7455
--- /dev/null
+++ b/fs/verity/measure.c
@@ -0,0 +1,57 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * fs/verity/measure.c: ioctl to get a verity file's measurement
+ *
+ * Copyright 2019 Google LLC
+ */
+
+#include "fsverity_private.h"
+
+#include <linux/uaccess.h>
+
+/**
+ * fsverity_ioctl_measure() - get a verity file's measurement
+ *
+ * Retrieve the file measurement that the kernel is enforcing for reads from a
+ * verity file. See the "FS_IOC_MEASURE_VERITY" section of
+ * Documentation/filesystems/fsverity.rst for the documentation.
+ *
+ * Return: 0 on success, -errno on failure
+ */
+int fsverity_ioctl_measure(struct file *filp, void __user *_uarg)
+{
+ const struct inode *inode = file_inode(filp);
+ struct fsverity_digest __user *uarg = _uarg;
+ const struct fsverity_info *vi;
+ const struct fsverity_hash_alg *hash_alg;
+ struct fsverity_digest arg;
+
+ vi = fsverity_get_info(inode);
+ if (!vi)
+ return -ENODATA; /* not a verity file */
+ hash_alg = vi->tree_params.hash_alg;
+
+ /*
+ * The user specifies the digest_size their buffer has space for; we can
+ * return the digest if it fits in the available space. We write back
+ * the actual size, which may be shorter than the user-specified size.
+ */
+
+ if (get_user(arg.digest_size, &uarg->digest_size))
+ return -EFAULT;
+ if (arg.digest_size < hash_alg->digest_size)
+ return -EOVERFLOW;
+
+ memset(&arg, 0, sizeof(arg));
+ arg.digest_algorithm = hash_alg - fsverity_hash_algs;
+ arg.digest_size = hash_alg->digest_size;
+
+ if (copy_to_user(uarg, &arg, sizeof(arg)))
+ return -EFAULT;
+
+ if (copy_to_user(uarg->digest, vi->measurement, hash_alg->digest_size))
+ return -EFAULT;
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(fsverity_ioctl_measure);
diff --git a/include/linux/fsverity.h b/include/linux/fsverity.h
index d1a5dbf450c46..3b6b8ccebe7d2 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)
--
2.22.0
