lkml.org 
[lkml]   [2022]   [Mar]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH v7 1/5] fs-verity: define a function to return the integrity protected file digest
From
On 2022/3/26 6:38, Mimi Zohar wrote:
> 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: Eric Biggers <ebiggers@google.com>
> Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
> ---
> fs/verity/Kconfig | 1 +
> fs/verity/fsverity_private.h | 7 ------
> fs/verity/measure.c | 43 ++++++++++++++++++++++++++++++++++++
> include/linux/fsverity.h | 18 +++++++++++++++
> 4 files changed, 62 insertions(+), 7 deletions(-)
>
> diff --git a/fs/verity/Kconfig b/fs/verity/Kconfig
> index 24d1b54de807..54598cd80145 100644
> --- a/fs/verity/Kconfig
> +++ b/fs/verity/Kconfig
> @@ -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
> diff --git a/fs/verity/fsverity_private.h b/fs/verity/fsverity_private.h
> index a7920434bae5..c6fb62e0ef1a 100644
> --- a/fs/verity/fsverity_private.h
> +++ b/fs/verity/fsverity_private.h
> @@ -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 */
> diff --git a/fs/verity/measure.c b/fs/verity/measure.c
> index f0d7b30c62db..e99c00350c28 100644
> --- a/fs/verity/measure.c
> +++ b/fs/verity/measure.c
> @@ -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);

Hi Mimi,

I would suggest moving this memset downward right before the memcpy.

> +
> + /* 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;
> +}
--
Best
GUO Zihua

\
 
 \ /
  Last update: 2022-03-28 05:46    [W:0.718 / U:0.548 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site