On 06/20, Eric Biggers wrote:
> 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 04b37475fd280a..6f7675ae0a3110 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 00000000000000..05049b68c74553
> --- /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 7ef2ef82653409..247359c86b72e0 100644
> --- a/include/linux/fsverity.h
> +++ b/include/linux/fsverity.h
> @@ -116,6 +116,10 @@ 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);
> @@ -143,6 +147,13 @@ 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)
> --
> 2.22.0.410.gd8fdbe21b5-goog
