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Commit ebeb6548 authored by Eric Biggers's avatar Eric Biggers Committed by Jaegeuk Kim
Browse files

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: default avatarTheodore Ts'o <tytso@mit.edu>
Reviewed-by: default avatarJaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: default avatarEric Biggers <ebiggers@google.com>
parent 43005f9b

fs/verity/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -3,5 +3,6 @@ 
obj-$(CONFIG_FS_VERITY) += enable.o \

			   hash_algs.o \

			   init.o \

			   measure.o \

			   open.o \

			   verify.o

fs/verity/measure.c

0 → 100644
+57 −0
Original line number Diff line number Diff line 
// 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);

include/linux/fsverity.h

+11 −0
Original line number Diff line number Diff line
@@ -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)