linux-kernel - Re: [PATCH 1/4] fs-verity: define a function to return the integrity protected file digest

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Date:   Mon, 29 Nov 2021 21:33:29 -0800
From:   Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
To:     Eric Biggers <ebiggers@...nel.org>,
        Mimi Zohar <zohar@...ux.ibm.com>
Cc:     linux-integrity@...r.kernel.org, linux-fscrypt@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] fs-verity: define a function to return the integrity
 protected file digest

Hi Mimi,

On 11/29/2021 6:19 PM, Eric Biggers wrote:
> Generally looks fine.  A few nits below:
> 
> On Mon, Nov 29, 2021 at 12:00:54PM -0500, Mimi Zohar wrote:
>> Define a function named fsverity_measure() to return the verity file digest
>> and the associated hash algorithm (enum hash_algo).
>>
>> Signed-off-by: Mimi Zohar <zohar@...ux.ibm.com>
>> ---
>>   fs/verity/fsverity_private.h |  6 -----
>>   fs/verity/measure.c          | 49 ++++++++++++++++++++++++++++++++++++
>>   include/linux/fsverity.h     | 17 +++++++++++++
>>   3 files changed, 66 insertions(+), 6 deletions(-)
>>
>> diff --git a/fs/verity/fsverity_private.h b/fs/verity/fsverity_private.h
>> index a7920434bae5..54c5f0993541 100644
>> --- a/fs/verity/fsverity_private.h
>> +++ b/fs/verity/fsverity_private.h
>> @@ -26,12 +26,6 @@ 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
> 
> The include of sha2.h should be removed from this file.
> 
>> +/**
>> + * fsverity_measure() - get a verity file's digest
nit: The function name seems to suggest it is measuring the fs-verity 
file's digest. Since it is reading the file's digest: 
fsverity_read_digest() or fsverity_read_measure()?

  -lakshmi

>> + * @inode: inode to get digest of
>> + * @digest: pointer to the digest
>> + * @alg: pointer to the hash algorithm enumeration
> 
> It should be made clear that @digest and @alg are output, for example:
> 
>   * @digest: (out) pointer to the digest
>   * @alg: (out) pointer to the hash algorithm enumeration
> 
>> + * Return the file hash algorithm, digest size, and digest of an fsverity
>> + * protected file.
> 
> The digest size is implied, not returned.
> 
>> +
>> +		if (!strcmp(hash_alg->name, hash_algo_name[i])) {
> 
> As the kernel test robot pointed out, this creates a dependency on
> CRYPTO_HASH_INFO.  So FS_VERITY will need to select CRYPTO_HASH_INFO.
> 
> - Eric
>