Re: [PATCH 4/4] ima: support fs-verity file digest based signatures

Lakshmi Ramasubramanian
2021-11-30T05:56:37Z

Hi Mimi,

On 11/29/2021 9:00 AM, Mimi Zohar wrote:
> Instead of calculating a file hash and verifying the signature stored
> in the security.ima xattr against the calculated file hash, verify the
> signature of the fs-verity's file digest. The fs-verity file digest is
> a hash that includes the Merkle tree root hash.
This patch is reading the fs-verity signature for the given file using
the new function fsverity_measure() that was defined in [Patch 1/4]. Is
it also verifying the fs-verity signature here?

>
> Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
> ---
> security/integrity/ima/ima_api.c | 20 ++++++++++++++++++++
> 1 file changed, 20 insertions(+)
>
> diff --git a/security/integrity/ima/ima_api.c b/security/integrity/ima/ima_api.c
> index 179c7f0364c2..ee1701f8c0f3 100644
> --- a/security/integrity/ima/ima_api.c
> +++ b/security/integrity/ima/ima_api.c
> @@ -16,6 +16,7 @@
> #include <linux/xattr.h>
> #include <linux/evm.h>
> #include <linux/iversion.h>
> +#include <linux/fsverity.h>
>
> #include "ima.h"
>
> @@ -205,6 +206,23 @@ int ima_get_action(struct user_namespace *mnt_userns, struct inode *inode,
> allowed_algos);
> }
>
> +static int ima_collect_verity_measurement(struct integrity_iint_cache *iint,
> + struct ima_digest_data *hash)
> +{
> + u8 verity_digest[FS_VERITY_MAX_DIGEST_SIZE];
> + enum hash_algo verity_alg;
> + int rc;
> +
> + rc = fsverity_measure(iint->inode, verity_digest, &verity_alg);
nit: fsverity_collect_measurement() may be more appropriate for this
function (defined in [PATCH 1/4]).

thanks,
-lakshmi

> + if (rc)
> + return -EINVAL;
> + if (hash->algo != verity_alg)
> + return -EINVAL;
> + hash->length = hash_digest_size[verity_alg];
> + memcpy(hash->digest, verity_digest, hash->length);
> + return 0;
> +}
> +
> /*
> * ima_collect_measurement - collect file measurement
> *
> @@ -256,6 +274,8 @@ int ima_collect_measurement(struct integrity_iint_cache *iint,
>
> if (buf)
> result = ima_calc_buffer_hash(buf, size, &hash.hdr);
> + else if (veritysig)
> + result = ima_collect_verity_measurement(iint, &hash.hdr);
> else
> result = ima_calc_file_hash(file, &hash.hdr);
>
>