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

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Message-ID: <CAHC9VhSamRVpgrDrSuc2dsbbw3-pvjDi9BsFWoWssHkAD2W5vA@mail.gmail.com>
Date:   Wed, 11 Jan 2023 09:25:56 -0500
From:   Paul Moore <paul@...l-moore.com>
To:     Roberto Sassu <roberto.sassu@...weicloud.com>
Cc:     zohar@...ux.ibm.com, 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, Jan 11, 2023 at 4:31 AM Roberto Sassu
<roberto.sassu@...weicloud.com> wrote:
> On Fri, 2023-01-06 at 16:14 -0500, Paul Moore wrote:
> > 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:
>
> Hi Paul
>
> thanks for the comments. With the patch set to move IMA and EVM to the
> LSM infrastructure we will be back to calling mmap_prot() only once,
> but I guess we could do anyway, as the patch (if accepted) would be
> likely backported to stable kernels.

I think there is value in fixing this now and keeping it separate from
the IMA-to-LSM work as they really are disjoint.

-- 
paul-moore.com