linux-kernel - Re: [PATCH v3 2/7] kexec: add call to LSM hook in original kexec

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Date:   Thu, 24 May 2018 15:50:03 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Mimi Zohar <zohar@...ux.vnet.ibm.com>
Cc:     linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, David Howells <dhowells@...hat.com>,
        "Luis R . Rodriguez" <mcgrof@...nel.org>,
        kexec@...ts.infradead.org, Andres Rodriguez <andresx7@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH v3 2/7] kexec: add call to LSM hook in original kexec_load syscall

Mimi Zohar <zohar@...ux.vnet.ibm.com> writes:

> In order for LSMs and IMA-appraisal to differentiate between the
> original and new syscalls, both the original and new syscalls must call
> an LSM hook.  This patch adds a call to security_kernel_read_data() in
> the original kexec syscall.

Until the lsm hook mess gets cleaned up.

Nacked-by: "Eric W. Biederman" <ebiederm@...ssion.com>

>
> Signed-off-by: Mimi Zohar <zohar@...ux.vnet.ibm.com>
> Cc: Eric Biederman <ebiederm@...ssion.com>
> Cc: Luis R. Rodriguez <mcgrof@...nel.org>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: David Howells <dhowells@...hat.com>
> ---
>  kernel/kexec.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/kernel/kexec.c b/kernel/kexec.c
> index aed8fb2564b3..061ada41c18c 100644
> --- a/kernel/kexec.c
> +++ b/kernel/kexec.c
> @@ -11,6 +11,7 @@
>  #include <linux/capability.h>
>  #include <linux/mm.h>
>  #include <linux/file.h>
> +#include <linux/security.h>
>  #include <linux/kexec.h>
>  #include <linux/mutex.h>
>  #include <linux/list.h>
> @@ -195,10 +196,17 @@ static int do_kexec_load(unsigned long entry, unsigned long nr_segments,
>  static inline int kexec_load_check(unsigned long nr_segments,
>  				   unsigned long flags)
>  {
> +	int result;
> +
>  	/* We only trust the superuser with rebooting the system. */
>  	if (!capable(CAP_SYS_BOOT) || kexec_load_disabled)
>  		return -EPERM;
>  
> +	/* Permit LSMs and IMA to fail the kexec */
> +	result = security_kernel_read_data(NULL, READING_KEXEC_IMAGE);
> +	if (result < 0)
> +		return result;
> +
>  	/*
>  	 * Verify we have a legal set of flags
>  	 * This leaves us room for future extensions.