Commit 246d9216 authored by Mimi Zohar's avatar Mimi Zohar
Browse files

fs-verity: define a function to return the integrity protected file digest 



Define a function named fsverity_get_digest() to return the verity file
digest and the associated hash algorithm (enum hash_algo).

This assumes that before calling fsverity_get_digest() the file must have
been opened, which is even true for the IMA measure/appraise on file
open policy rule use case (func=FILE_CHECK).  do_open() calls vfs_open()
immediately prior to ima_file_check().

Acked-by: default avatarEric Biggers <ebiggers@google.com>
Signed-off-by: default avatarMimi Zohar <zohar@linux.ibm.com>
parent 09091c44

fs/verity/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -3,6 +3,7 @@ 
config FS_VERITY

	bool "FS Verity (read-only file-based authenticity protection)"

	select CRYPTO

	select CRYPTO_HASH_INFO

	# SHA-256 is implied as it's intended to be the default hash algorithm.

	# To avoid bloat, other wanted algorithms must be selected explicitly.

	# Note that CRYPTO_SHA256 denotes the generic C implementation, but

fs/verity/fsverity_private.h

+0 −7
Original line number Diff line number Diff line
@@ -14,7 +14,6 @@ 


#define pr_fmt(fmt) "fs-verity: " fmt



#include <crypto/sha2.h>

#include <linux/fsverity.h>

#include <linux/mempool.h>
@@ -26,12 +25,6 @@ struct ahash_request; 
 */

#define FS_VERITY_MAX_LEVELS		8



/*

 * Largest digest size among all hash algorithms supported by fs-verity.

 * Currently assumed to be <= size of fsverity_descriptor::root_hash.

 */

#define FS_VERITY_MAX_DIGEST_SIZE	SHA512_DIGEST_SIZE



/* A hash algorithm supported by fs-verity */

struct fsverity_hash_alg {

	struct crypto_ahash *tfm; /* hash tfm, allocated on demand */

fs/verity/measure.c

+43 −0
Original line number Diff line number Diff line
@@ -57,3 +57,46 @@ int fsverity_ioctl_measure(struct file *filp, void __user *_uarg) 
	return 0;

}

EXPORT_SYMBOL_GPL(fsverity_ioctl_measure);



/**

 * fsverity_get_digest() - get a verity file's digest

 * @inode: inode to get digest of

 * @digest: (out) pointer to the digest

 * @alg: (out) pointer to the hash algorithm enumeration

 *

 * Return the file hash algorithm and digest of an fsverity protected file.

 * Assumption: before calling fsverity_get_digest(), the file must have been

 * opened.

 *

 * Return: 0 on success, -errno on failure

 */

int fsverity_get_digest(struct inode *inode,

			u8 digest[FS_VERITY_MAX_DIGEST_SIZE],

			enum hash_algo *alg)

{

	const struct fsverity_info *vi;

	const struct fsverity_hash_alg *hash_alg;

	int i;



	vi = fsverity_get_info(inode);

	if (!vi)

		return -ENODATA; /* not a verity file */



	hash_alg = vi->tree_params.hash_alg;

	memset(digest, 0, FS_VERITY_MAX_DIGEST_SIZE);



	/* convert the verity hash algorithm name to a hash_algo_name enum */

	i = match_string(hash_algo_name, HASH_ALGO__LAST, hash_alg->name);

	if (i < 0)

		return -EINVAL;

	*alg = i;



	if (WARN_ON_ONCE(hash_alg->digest_size != hash_digest_size[*alg]))

		return -EINVAL;

	memcpy(digest, vi->file_digest, hash_alg->digest_size);



	pr_debug("file digest %s:%*phN\n", hash_algo_name[*alg],

		 hash_digest_size[*alg], digest);



	return 0;

}

include/linux/fsverity.h

+18 −0
Original line number Diff line number Diff line
@@ -12,8 +12,16 @@ 
#define _LINUX_FSVERITY_H



#include <linux/fs.h>

#include <crypto/hash_info.h>

#include <crypto/sha2.h>

#include <uapi/linux/fsverity.h>



/*

 * Largest digest size among all hash algorithms supported by fs-verity.

 * Currently assumed to be <= size of fsverity_descriptor::root_hash.

 */

#define FS_VERITY_MAX_DIGEST_SIZE	SHA512_DIGEST_SIZE



/* Verity operations for filesystems */

struct fsverity_operations {
@@ -131,6 +139,9 @@ int fsverity_ioctl_enable(struct file *filp, const void __user *arg); 
/* measure.c */



int fsverity_ioctl_measure(struct file *filp, void __user *arg);

int fsverity_get_digest(struct inode *inode,

			u8 digest[FS_VERITY_MAX_DIGEST_SIZE],

			enum hash_algo *alg);



/* open.c */
@@ -170,6 +181,13 @@ static inline int fsverity_ioctl_measure(struct file *filp, void __user *arg) 
	return -EOPNOTSUPP;

}



static inline int fsverity_get_digest(struct inode *inode,

				      u8 digest[FS_VERITY_MAX_DIGEST_SIZE],

				      enum hash_algo *alg)

{

	return -EOPNOTSUPP;

}



/* open.c */



static inline int fsverity_file_open(struct inode *inode, struct file *filp)