linux-kernel - Re: [PATCH v2] security: Restore passing final prot to ima_file

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Message-ID: <CAHC9VhQUAuF-Fan72j7BOqOdLE=B=mJpJ_GpR5p5cUmXruYT=Q@mail.gmail.com>
Date:   Fri, 6 Jan 2023 16:14:47 -0500
From:   Paul Moore <paul@...l-moore.com>
To:     Roberto Sassu <roberto.sassu@...weicloud.com>, zohar@...ux.ibm.com
Cc:     jmorris@...ei.org, serge@...lyn.com,
        linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, viro@...iv.linux.org.uk,
        Roberto Sassu <roberto.sassu@...wei.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH v2] security: Restore passing final prot to ima_file_mmap()

On Wed, Dec 21, 2022 at 9:10 AM Roberto Sassu
<roberto.sassu@...weicloud.com> wrote:
>
> From: Roberto Sassu <roberto.sassu@...wei.com>
>
> Commit 98de59bfe4b2f ("take calculation of final prot in
> security_mmap_file() into a helper") moved the code to update prot with the
> actual protection flags to be granted to the requestor by the kernel to a
> helper called mmap_prot(). However, the patch didn't update the argument
> passed to ima_file_mmap(), making it receive the requested prot instead of
> the final computed prot.
>
> A possible consequence is that files mmapped as executable might not be
> measured/appraised if PROT_EXEC is not requested but subsequently added in
> the final prot.
>
> Replace prot with mmap_prot(file, prot) as the second argument of
> ima_file_mmap() to restore the original behavior.
>
> Cc: stable@...r.kernel.org
> Fixes: 98de59bfe4b2 ("take calculation of final prot in security_mmap_file() into a helper")
> Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
> ---
>  security/security.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/security/security.c b/security/security.c
> index d1571900a8c7..0d2359d588a1 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -1666,7 +1666,7 @@ int security_mmap_file(struct file *file, unsigned long prot,
>                                         mmap_prot(file, prot), flags);
>         if (ret)
>                 return ret;
> -       return ima_file_mmap(file, prot);
> +       return ima_file_mmap(file, mmap_prot(file, prot));
>  }

This seems like a reasonable fix, although as the original commit is
~10 years old at this point I am a little concerned about the impact
this might have on IMA.  Mimi, what do you think?

Beyond that, my only other comment would be to only call mmap_prot()
once and cache the results in a local variable.  You could also fix up
some of the ugly indentation crimes in security_mmap_file() while you
are at it, e.g. something like this:

diff --git a/security/security.c b/security/security.c
index d1571900a8c7..2f9cad9ecac8 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1662,11 +1662,12 @@ int security_mmap_file(struct file *file, unsigned long
prot,
                       unsigned long flags)
{
       int ret;
-       ret = call_int_hook(mmap_file, 0, file, prot,
-                                       mmap_prot(file, prot), flags);
+       unsigned long prot_adj = mmap_prot(file, prot);
+
+       ret = call_int_hook(mmap_file, 0, file, prot, prot_adj, flags);
       if (ret)
               return ret;
-       return ima_file_mmap(file, prot);
+       return ima_file_mmap(file, prot_adj);
}

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