Re: [PATCH V34 21/29] Lock down /proc/kcore

Kees Cook
2019-06-23T00:05:33Z

On Fri, Jun 21, 2019 at 05:03:50PM -0700, Matthew Garrett wrote:
> From: David Howells <dhowells@redhat.com>
>
> Disallow access to /proc/kcore when the kernel is locked down to prevent
> access to cryptographic data. This is limited to lockdown
> confidentiality mode and is still permitted in integrity mode.
>
> Signed-off-by: David Howells <dhowells@redhat.com>
> Signed-off-by: Matthew Garrett <mjg59@google.com>
> ---
> fs/proc/kcore.c | 5 +++++
> include/linux/security.h | 1 +
> security/lockdown/lockdown.c | 1 +
> 3 files changed, 7 insertions(+)
>
> diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
> index d29d869abec1..4e95edb1e282 100644
> --- a/fs/proc/kcore.c
> +++ b/fs/proc/kcore.c
> @@ -31,6 +31,7 @@
> #include <linux/ioport.h>
> #include <linux/memory.h>
> #include <linux/sched/task.h>
> +#include <linux/security.h>
> #include <asm/sections.h>
> #include "internal.h"
>
> @@ -545,6 +546,10 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
>
> static int open_kcore(struct inode *inode, struct file *filp)
> {
> + int ret = security_locked_down(LOCKDOWN_KCORE);
> +
> + if (ret)
> + return ret;
> if (!capable(CAP_SYS_RAWIO))
> return -EPERM;

Another capable() check ordering fix needed. With that:

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

>
> diff --git a/include/linux/security.h b/include/linux/security.h
> index c649cb91e762..3875f6df2ecc 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -95,6 +95,7 @@ enum lockdown_reason {
> LOCKDOWN_MODULE_PARAMETERS,
> LOCKDOWN_MMIOTRACE,
> LOCKDOWN_INTEGRITY_MAX,
> + LOCKDOWN_KCORE,
> LOCKDOWN_CONFIDENTIALITY_MAX,
> };
>
> diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
> index cd86ed9f4d4b..4c9b324dfc55 100644
> --- a/security/lockdown/lockdown.c
> +++ b/security/lockdown/lockdown.c
> @@ -31,6 +31,7 @@ static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {
> [LOCKDOWN_MODULE_PARAMETERS] = "unsafe module parameters",
> [LOCKDOWN_MMIOTRACE] = "unsafe mmio",
> [LOCKDOWN_INTEGRITY_MAX] = "integrity",
> + [LOCKDOWN_KCORE] = "/proc/kcore access",
> [LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
> };
>
> --
> 2.22.0.410.gd8fdbe21b5-goog
>

--
Kees Cook