linux-kernel - Re: [PATCH v10 2/8] ima: define and call ima_alloc_kexec_file

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Message-ID: <a8368f2402e1145c134e445d015c434140874e06.camel@linux.ibm.com>
Date: Thu, 20 Mar 2025 09:06:13 -0400
From: Mimi Zohar <zohar@...ux.ibm.com>
To: Baoquan He <bhe@...hat.com>
Cc: steven chen <chenste@...ux.microsoft.com>, stefanb@...ux.ibm.com,
        roberto.sassu@...weicloud.com, roberto.sassu@...wei.com,
        eric.snowberg@...cle.com, ebiederm@...ssion.com, paul@...l-moore.com,
        code@...icks.com, bauermann@...abnow.com,
        linux-integrity@...r.kernel.org, kexec@...ts.infradead.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org,
        madvenka@...ux.microsoft.com, nramas@...ux.microsoft.com,
        James.Bottomley@...senpartnership.com, vgoyal@...hat.com,
        dyoung@...hat.com
Subject: Re: [PATCH v10 2/8] ima: define and call ima_alloc_kexec_file_buf()

On Thu, 2025-03-20 at 09:51 +0800, Baoquan He wrote:
> > > > diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
> > > > index 8567619889d1..45170e283272 100644
> > > > --- a/security/integrity/ima/ima_kexec.c
> > > > +++ b/security/integrity/ima/ima_kexec.c
> > > > @@ -15,6 +15,48 @@
> > > >   #include "ima.h"
> > > >   
> > > >   #ifdef CONFIG_IMA_KEXEC
> > > > +static struct seq_file ima_kexec_file;
> > > > +
> > > > +static void ima_reset_kexec_file(struct seq_file *sf)
> > > > +{
> > > > +	sf->buf = NULL;
> > > > +	sf->size = 0;
> > > > +	sf->read_pos = 0;
> > > > +	sf->count = 0;
> > > > +}
> > > > +
> > > > +static void ima_free_kexec_file_buf(struct seq_file *sf)
> > > > +{
> > > > +	vfree(sf->buf);
> > > > +	ima_reset_kexec_file(sf);
> > > > +}
> > > > +
> > > > +static int ima_alloc_kexec_file_buf(size_t segment_size)
> > > > +{
> > > > +	/*
> > > > +	 * kexec 'load' may be called multiple times.
> > > > +	 * Free and realloc the buffer only if the segment_size is
> > > > +	 * changed from the previous kexec 'load' call.
> > > > +	 */
> > > > +	if (ima_kexec_file.buf && ima_kexec_file.size == segment_size)
> > > > +		goto out;
> > 
> > The call to ima_reset_kexec_file() in ima_add_kexec_buffer() resets
> > ima_kexec_file.buf() hiding the fact that the above test always fails and falls
> > through.  As a result, 'buf' is always being re-allocated.

Hi Steven,

[Reiterating the comment in the "ima: kexec: move IMA log copy from kexec load
to execute" thread, here, for completeness.]

Instead of adding and then removing the ima_reset_kexec_file() call from
ima_add_kexec_buffer(), defer adding the segment size test to when it is
actually possible for the segment size to change. Please make the segment size
test as a separate patch.

ima_reset_kexec_file() will then only be called by ima_free_kexec_file_buf(). 
Inline the ima_reset_kexec_file() code in ima_free_kexec_file_buf().

thanks,

Mimi