linux-kernel - Re: [PATCH v2 2/2] ima: Alloc ima_max_digest_data in xattr_verify() if CONFIG_VMAP

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Date:   Thu, 1 Dec 2022 10:55:27 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     Roberto Sassu <roberto.sassu@...weicloud.com>
Cc:     zohar@...ux.ibm.com, dmitry.kasatkin@...il.com,
        paul@...l-moore.com, jmorris@...ei.org, serge@...lyn.com,
        linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Roberto Sassu <roberto.sassu@...wei.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH v2 2/2] ima: Alloc ima_max_digest_data in xattr_verify()
 if CONFIG_VMAP_STACK=y

On Thu, Dec 01, 2022 at 11:06:25AM +0100, Roberto Sassu wrote:
> From: Roberto Sassu <roberto.sassu@...wei.com>
> 
> Similarly to evm_verify_hmac(), which allocates an evm_digest structure to
> satisfy the linear mapping requirement if CONFIG_VMAP_STACK is enabled, do
> the same in xattr_verify(). Allocate an ima_max_digest_data structure and
> use that instead of the in-stack counterpart.
> 
> Cc: stable@...r.kernel.org # 4.9.x
> Fixes: ba14a194a434 ("fork: Add generic vmalloced stack support")
> Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>

Likewise, what is the actual problem here?  Where specifically is a scatterlist
being used to represent an on-stack buffer?

- Eric