linux-kernel - Re: [PATCH 3/5] ima: Fix ima digest hash table key calculation

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Message-Id: <1587588987.5165.20.camel@linux.ibm.com>
Date:   Wed, 22 Apr 2020 16:56:27 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Roberto Sassu <roberto.sassu@...wei.com>
Cc:     linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, krzysztof.struczynski@...wei.com,
        silviu.vlasceanu@...wei.com, stable@...r.kernel.org
Subject: Re: [PATCH 3/5] ima: Fix ima digest hash table key calculation

Hi Roberto, Krsysztof,

On Wed, 2020-03-25 at 17:11 +0100, Roberto Sassu wrote:
> From: Krzysztof Struczynski <krzysztof.struczynski@...wei.com>
> 
> Function hash_long() accepts unsigned long, while currently only one byte
> is passed from ima_hash_key(), which calculates a key for ima_htable. Use
> more bytes to avoid frequent collisions.
> 
> Length of the buffer is not explicitly passed as a function parameter,
> because this function expects a digest whose length is greater than the
> size of unsigned long.

Somehow I missed the original report of this problem https://lore.kern
el.org/patchwork/patch/674684/.  This patch is definitely better, but
how many unique keys are actually being used?  Is it anywhere near
IMA_MEASURE_HTABLE_SIZE(512)?

Do we need a new securityfs entry to display the number used?

Mimi

> 
> Cc: stable@...r.kernel.org
> Fixes: 3323eec921ef ("integrity: IMA as an integrity service provider")
> Signed-off-by: Krzysztof Struczynski <krzysztof.struczynski@...wei.com>
> ---
>  security/integrity/ima/ima.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> index 64317d95363e..cf0022c2bc14 100644
> --- a/security/integrity/ima/ima.h
> +++ b/security/integrity/ima/ima.h
> @@ -177,7 +177,7 @@ extern struct ima_h_table ima_htable;
>  
>  static inline unsigned long ima_hash_key(u8 *digest)
>  {
> -	return hash_long(*digest, IMA_HASH_BITS);
> +	return hash_long(*((unsigned long *)digest), IMA_HASH_BITS);
>  }
>  
>  #define __ima_hooks(hook)		\