kernel-hardening.lists.openwall.com archive mirror
 help / color / mirror / Atom feed
From: John Wood <john.wood@gmx.com>
To: Alexander Lobakin <alobakin@pm.me>
Cc: John Wood <john.wood@gmx.com>, Kees Cook <keescook@chromium.org>,
	Jann Horn <jannh@google.com>, Jonathan Corbet <corbet@lwn.net>,
	James Morris <jmorris@namei.org>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	Shuah Khan <shuah@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	Arnd Bergmann <arnd@arndb.de>, Andi Kleen <ak@linux.intel.com>,
	valdis.kletnieks@vt.edu,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Randy Dunlap <rdunlap@infradead.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-security-module@vger.kernel.org,
	linux-kselftest@vger.kernel.org, linux-arch@vger.kernel.org,
	linux-hardening@vger.kernel.org,
	kernel-hardening@lists.openwall.com
Subject: Re: [PATCH v8 3/8] security/brute: Detect a brute force attack
Date: Fri, 2 Jul 2021 16:59:54 +0200	[thread overview]
Message-ID: <20210702145954.GA4513@ubuntu> (raw)
In-Reply-To: <20210701234807.50453-1-alobakin@pm.me>

Hi,

On Thu, Jul 01, 2021 at 11:55:14PM +0000, Alexander Lobakin wrote:
> Hi,
>
> From: John Wood <john.wood@gmx.com>
> Date: Sat, 5 Jun 2021 17:04:00 +0200
>
> > +static int brute_task_execve(struct linux_binprm *bprm, struct file *file)
> > +{
> > +	struct dentry *dentry = file_dentry(bprm->file);
> > +	struct inode *inode = file_inode(bprm->file);
> > +	struct brute_stats stats;
> > +	int rc;
> > +
> > +	inode_lock(inode);
> > +	rc = brute_get_xattr_stats(dentry, inode, &stats);
> > +	if (WARN_ON_ONCE(rc && rc != -ENODATA))
> > +		goto unlock;
>
> I think I caught a problem here. Have you tested this with
> initramfs?

No, it has not been tested with initramfs :(

> According to init/do_mount.c's
> init_rootfs()/rootfs_init_fs_context(), when `root=` cmdline
> parameter is not empty, kernel creates rootfs of type ramfs
> (tmpfs otherwise).
> The thing about ramfs is that it doesn't support xattrs.

It is a known issue that systems without xattr support are not
suitable for Brute (there are a note in the documentation).
However, the purpose is not to panic the system :(

> I'm running this v8 on a regular PC with initramfs and having
> `root=` in cmdline, and Brute doesn't allow the kernel to run
> any init processes (/init, /sbin/init, ...) with err == -95
> (-EOPNOTSUPP) -- I'm getting a
>
> WARNING: CPU: 0 PID: 173 at brute_task_execve+0x15d/0x200
> <snip>
> Failed to execute /init (error -95)
>
> and so on (and a panic at the end).
>
> If I omit `root=` from cmdline, then the kernel runs init process
> just fine -- I guess because initramfs is then placed inside tmpfs
> with xattr support.
>
> As for me, this ramfs/tmpfs selection based on `root=` presence
> is ridiculous and I don't see or know any reasons behind that.
> But that's another story, and ramfs might be not the only one
> system without xattr support.
> I think Brute should have a fallback here, e.g. it could simply
> ignore files from xattr-incapable filesystems instead of such
> WARNING splats and stuff.

Ok, it seems reasonable to me: if the file system doesn't support
xattr, but Brute is enabled, Brute will do nothing and the system
will work normally.

I will work on it for the next version.
Thanks for the feedback.

John Wood

  reply	other threads:[~2021-07-02 15:01 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-01 23:55 [PATCH v8 3/8] security/brute: Detect a brute force attack Alexander Lobakin
2021-07-02 14:59 ` John Wood [this message]
2021-07-02 17:08   ` Alexander Lobakin
2021-07-03 10:59     ` John Wood
2021-07-04 14:01       ` John Wood
2021-07-05 12:52         ` Alexander Lobakin
  -- strict thread matches above, loose matches on Subject: below --
2021-06-05 15:03 [PATCH v8 0/8] Fork brute force attack mitigation John Wood
2021-06-05 15:04 ` [PATCH v8 3/8] security/brute: Detect a brute force attack John Wood

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=20210702145954.GA4513@ubuntu \
    --to=john.wood@gmx.com \
    --cc=ak@linux.intel.com \
    --cc=akpm@linux-foundation.org \
    --cc=alobakin@pm.me \
    --cc=arnd@arndb.de \
    --cc=bp@alien8.de \
    --cc=corbet@lwn.net \
    --cc=gregkh@linuxfoundation.org \
    --cc=hpa@zytor.com \
    --cc=jannh@google.com \
    --cc=jmorris@namei.org \
    --cc=keescook@chromium.org \
    --cc=kernel-hardening@lists.openwall.com \
    --cc=linux-arch@vger.kernel.org \
    --cc=linux-doc@vger.kernel.org \
    --cc=linux-hardening@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-kselftest@vger.kernel.org \
    --cc=linux-security-module@vger.kernel.org \
    --cc=mingo@redhat.com \
    --cc=rdunlap@infradead.org \
    --cc=serge@hallyn.com \
    --cc=shuah@kernel.org \
    --cc=tglx@linutronix.de \
    --cc=valdis.kletnieks@vt.edu \
    --cc=x86@kernel.org \
    /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).