From: Laszlo Ersek <lersek@redhat.com>
To: Javier Martinez Canillas <javierm@redhat.com>,
linux-kernel@vger.kernel.org
Cc: Ivan Hu <ivan.hu@canonical.com>,
linux-efi@vger.kernel.org, Laura Abbott <labbott@redhat.com>,
Josh Boyer <jwboyer@redhat.com>, Peter Jones <pjones@redhat.com>,
Ard Biesheuvel <ard.biesheuvel@linaro.org>,
Janne Karhunen <janne.karhunen@gmail.com>,
Kees Cook <keescook@chromium.org>,
David Howells <dhowells@redhat.com>,
linux-security-module@vger.kernel.org,
Casey Schaufler <casey@schaufler-ca.com>,
Micah Morton <mortonm@chromium.org>,
"Steven Rostedt (VMware)" <rostedt@goodmis.org>,
James Morris <jmorris@namei.org>,
Al Viro <viro@zeniv.linux.org.uk>,
Matthew Garrett <matthewgarrett@google.com>,
"Serge E. Hallyn" <serge@hallyn.com>
Subject: Re: [PATCH v2] efi/efi_test: lock down /dev/efi_test and require CAP_SYS_ADMIN
Date: Tue, 8 Oct 2019 20:15:27 +0200 [thread overview]
Message-ID: <affd623b-2e9f-cb10-f9e8-c14b8c5f186c@redhat.com> (raw)
In-Reply-To: <20191008105510.6975-1-javierm@redhat.com>
On 10/08/19 12:55, Javier Martinez Canillas wrote:
> The driver exposes EFI runtime services to user-space through an IOCTL
> interface, calling the EFI services function pointers directly without
> using the efivar API.
>
> Disallow access to the /dev/efi_test character device when the kernel is
> locked down to prevent arbitrary user-space to call EFI runtime services.
>
> Also require CAP_SYS_ADMIN to open the chardev to prevent unprivileged
> users to call the EFI runtime services, instead of just relying on the
> chardev file mode bits for this.
>
> The main user of this driver is the fwts [0] tool that already checks if
> the effective user ID is 0 and fails otherwise. So this change shouldn't
> cause any regression to this tool.
>
> [0]: https://wiki.ubuntu.com/FirmwareTestSuite/Reference/uefivarinfo
>
> Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
> Acked-by: Laszlo Ersek <lersek@redhat.com>
>
> ---
>
> Changes in v2:
> - Also disable /dev/efi_test access when the kernel is locked down as
> suggested by Matthew Garrett.
Right; if you remember the pre-patch discussion off-list, we kind of
expected that lockdown might affect this. :)
... And, I can see Matt's comment now, at
<https://bugzilla.redhat.com/show_bug.cgi?id=1759325#c1>. Thanks for that!
While this change decreases the usability of the module, I fully agree
it is justified for production use. While it's more convenient for me to
keep SB enabled in the test VM(s) in general, and just run the test
whenever I need it, security trumps convenience. I can disable SB when
necessary, or even dedicate separate VMs (with SB generally disabled) to
this kind of testing.
> - Add Acked-by tag from Laszlo Ersek.
My ACK stands -- I don't know enough to validate the
security_locked_down() call and its friends, but I'm OK with the intent.
Thanks all!
Laszlo
>
> drivers/firmware/efi/test/efi_test.c | 8 ++++++++
> include/linux/security.h | 1 +
> security/lockdown/lockdown.c | 1 +
> 3 files changed, 10 insertions(+)
>
> diff --git a/drivers/firmware/efi/test/efi_test.c b/drivers/firmware/efi/test/efi_test.c
> index 877745c3aaf..7baf48c01e7 100644
> --- a/drivers/firmware/efi/test/efi_test.c
> +++ b/drivers/firmware/efi/test/efi_test.c
> @@ -14,6 +14,7 @@
> #include <linux/init.h>
> #include <linux/proc_fs.h>
> #include <linux/efi.h>
> +#include <linux/security.h>
> #include <linux/slab.h>
> #include <linux/uaccess.h>
>
> @@ -717,6 +718,13 @@ static long efi_test_ioctl(struct file *file, unsigned int cmd,
>
> static int efi_test_open(struct inode *inode, struct file *file)
> {
> + int ret = security_locked_down(LOCKDOWN_EFI_TEST);
> +
> + if (ret)
> + return ret;
> +
> + if (!capable(CAP_SYS_ADMIN))
> + return -EACCES;
> /*
> * nothing special to do here
> * We do accept multiple open files at the same time as we
> diff --git a/include/linux/security.h b/include/linux/security.h
> index a8d59d612d2..9df7547afc0 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -105,6 +105,7 @@ enum lockdown_reason {
> LOCKDOWN_NONE,
> LOCKDOWN_MODULE_SIGNATURE,
> LOCKDOWN_DEV_MEM,
> + LOCKDOWN_EFI_TEST,
> LOCKDOWN_KEXEC,
> LOCKDOWN_HIBERNATION,
> LOCKDOWN_PCI_ACCESS,
> diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
> index 8a10b43daf7..40b790536de 100644
> --- a/security/lockdown/lockdown.c
> +++ b/security/lockdown/lockdown.c
> @@ -20,6 +20,7 @@ static const char *const lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {
> [LOCKDOWN_NONE] = "none",
> [LOCKDOWN_MODULE_SIGNATURE] = "unsigned module loading",
> [LOCKDOWN_DEV_MEM] = "/dev/mem,kmem,port",
> + [LOCKDOWN_EFI_TEST] = "/dev/efi_test access",
> [LOCKDOWN_KEXEC] = "kexec of unsigned images",
> [LOCKDOWN_HIBERNATION] = "hibernation",
> [LOCKDOWN_PCI_ACCESS] = "direct PCI access",
>
next prev parent reply other threads:[~2019-10-08 18:15 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-08 10:55 [PATCH v2] efi/efi_test: lock down /dev/efi_test and require CAP_SYS_ADMIN Javier Martinez Canillas
2019-10-08 18:15 ` Laszlo Ersek [this message]
2019-10-09 2:17 ` Matthew Garrett
2019-10-09 13:02 ` Ard Biesheuvel
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=affd623b-2e9f-cb10-f9e8-c14b8c5f186c@redhat.com \
--to=lersek@redhat.com \
--cc=ard.biesheuvel@linaro.org \
--cc=casey@schaufler-ca.com \
--cc=dhowells@redhat.com \
--cc=ivan.hu@canonical.com \
--cc=janne.karhunen@gmail.com \
--cc=javierm@redhat.com \
--cc=jmorris@namei.org \
--cc=jwboyer@redhat.com \
--cc=keescook@chromium.org \
--cc=labbott@redhat.com \
--cc=linux-efi@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-security-module@vger.kernel.org \
--cc=matthewgarrett@google.com \
--cc=mortonm@chromium.org \
--cc=pjones@redhat.com \
--cc=rostedt@goodmis.org \
--cc=serge@hallyn.com \
--cc=viro@zeniv.linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).