From: John Wood <john.wood@gmx.com>
To: Jann Horn <jannh@google.com>
Cc: John Wood <john.wood@gmx.com>, Kees Cook <keescook@chromium.org>,
Kernel Hardening <kernel-hardening@lists.openwall.com>,
Matthew Wilcox <willy@infradead.org>,
Jonathan Corbet <corbet@lwn.net>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
Luis Chamberlain <mcgrof@kernel.org>,
Iurii Zaikin <yzaikin@google.com>,
James Morris <jmorris@namei.org>,
"Serge E. Hallyn" <serge@hallyn.com>,
linux-doc@vger.kernel.org,
kernel list <linux-kernel@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
linux-security-module <linux-security-module@vger.kernel.org>
Subject: Re: [RFC PATCH 5/6] security/fbfam: Detect a fork brute force attack
Date: Tue, 15 Sep 2020 19:36:27 +0200 [thread overview]
Message-ID: <20200915173627.GA2900@ubuntu> (raw)
In-Reply-To: <CAG48ez3aQXb3EuGRVvLLo7BxycqJ4Y2mL83QhY9-QMK_qkfCuQ@mail.gmail.com>
Hi,
On Mon, Sep 14, 2020 at 09:39:10PM +0200, Jann Horn wrote:
> On Sun, Sep 13, 2020 at 6:56 PM John Wood <john.wood@gmx.com> wrote:
> > On Fri, Sep 11, 2020 at 02:01:56AM +0200, Jann Horn wrote:
> > > On Fri, Sep 11, 2020 at 1:49 AM Kees Cook <keescook@chromium.org> wrote:
> > > > On Thu, Sep 10, 2020 at 01:21:06PM -0700, Kees Cook wrote:
> > > > [...]
> > > > I don't think this is the right place for detecting a crash -- isn't
> > > > this only for the "dumping core" condition? In other words, don't you
> > > > want to do this in get_signal()'s "fatal" block? (i.e. very close to the
> > > > do_coredump, but without the "should I dump?" check?)
> > > >
> > > > Hmm, but maybe I'm wrong? It looks like you're looking at noticing the
> > > > process taking a signal from SIG_KERNEL_COREDUMP_MASK ?
> > > >
> > > > (Better yet: what are fatal conditions that do NOT match
> > > > SIG_KERNEL_COREDUMP_MASK, and should those be covered?)
> > > >
> > > > Regardless, *this* looks like the only place without an LSM hook. And it
> > > > doesn't seem unreasonable to add one here. I assume it would probably
> > > > just take the siginfo pointer, which is also what you're checking.
> > >
> > > Good point, making this an LSM might be a good idea.
> > >
> > > > e.g. for include/linux/lsm_hook_defs.h:
> > > >
> > > > LSM_HOOK(int, 0, task_coredump, const kernel_siginfo_t *siginfo);
> > >
> > > I guess it should probably be an LSM_RET_VOID hook? And since, as you
> > > said, it's not really semantically about core dumping, maybe it should
> > > be named task_fatal_signal or something like that.
> >
> > If I understand correctly you propose to add a new LSM hook without return
> > value and place it here:
> >
> > diff --git a/kernel/signal.c b/kernel/signal.c
> > index a38b3edc6851..074492d23e98 100644
> > --- a/kernel/signal.c
> > +++ b/kernel/signal.c
> > @@ -2751,6 +2751,8 @@ bool get_signal(struct ksignal *ksig)
> > do_coredump(&ksig->info);
> > }
> >
> > + // Add the new LSM hook here
> > +
> > /*
> > * Death signals, no core dump.
> > */
>
> It should probably be in the "if (sig_kernel_coredump(signr)) {"
> branch. And I'm not sure whether it should be before or after
> do_coredump() - if you do it after do_coredump(), the hook will have
> to wait until the core dump file has been written, which may take a
> little bit of time.
But if the LSM hook is placed in the "if (sig_kernel_coredump(signr)) {"
branch, then only the following signals will be passed to it.
SIGQUIT, SIGILL, SIGTRAP, SIGABRT, SIGFPE, SIGSEGV, SIGBUS, SIGSYS,
SIGXCPU, SIGXFSZ, SIGEMT
The above signals are extracted from SIG_KERNEL_COREDUMP_MASK macro, and
are only related to coredump.
So, if we add a new LSM hook (named task_fatal_signal) to detect a fatal
signal it would be better to place it just above the if statement.
diff --git a/kernel/signal.c b/kernel/signal.c
index a38b3edc6851..406af87f2f96 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2736,6 +2736,8 @@ bool get_signal(struct ksignal *ksig)
*/
current->flags |= PF_SIGNALED;
+ // Place the new LSM hook here
+
if (sig_kernel_coredump(signr)) {
if (print_fatal_signals)
print_fatal_signal(ksig->info.si_signo);
This way all the fatal signals are caught and we also avoid the commented
delay if a core dump is necessary.
Thanks,
John Wood
next prev parent reply other threads:[~2020-09-15 17:38 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-10 20:21 [RESEND][RFC PATCH 0/6] Fork brute force attack mitigation (fbfam) Kees Cook
2020-09-10 20:21 ` [RFC PATCH 1/6] security/fbfam: Add a Kconfig to enable the fbfam feature Kees Cook
2020-09-10 21:21 ` Jann Horn
2020-09-17 17:32 ` John Wood
2020-09-10 23:18 ` Kees Cook
2020-09-17 18:40 ` John Wood
2020-09-17 22:05 ` Kees Cook
2020-09-18 14:50 ` John Wood
2020-09-10 20:21 ` [RFC PATCH 2/6] security/fbfam: Add the api to manage statistics Kees Cook
2020-09-10 23:23 ` Kees Cook
2020-09-10 20:21 ` [RFC PATCH 3/6] security/fbfam: Use " Kees Cook
2020-09-10 20:27 ` Jann Horn
2020-09-10 23:33 ` Kees Cook
2020-09-29 23:47 ` Steven Rostedt
2020-09-29 23:49 ` Steven Rostedt
2020-10-03 9:52 ` John Wood
2020-09-10 20:21 ` [RFC PATCH 4/6] security/fbfam: Add a new sysctl to control the crashing rate threshold Kees Cook
2020-09-10 23:14 ` Kees Cook
2020-09-13 14:33 ` John Wood
2020-09-10 20:21 ` [RFC PATCH 5/6] security/fbfam: Detect a fork brute force attack Kees Cook
2020-09-10 21:10 ` Jann Horn
2020-09-13 17:54 ` John Wood
2020-09-14 19:42 ` Jann Horn
2020-09-15 18:44 ` John Wood
2020-09-10 23:49 ` Kees Cook
2020-09-11 0:01 ` Jann Horn
2020-09-13 16:56 ` John Wood
2020-09-14 19:39 ` Jann Horn
2020-09-15 17:36 ` John Wood [this message]
2020-09-10 20:21 ` [RFC PATCH 6/6] security/fbfam: Mitigate " Kees Cook
2020-09-10 20:55 ` Jann Horn
2020-09-10 23:56 ` Kees Cook
2020-09-11 0:20 ` Jann Horn
2020-09-18 16:02 ` John Wood
2020-09-18 21:35 ` Kees Cook
2020-09-19 8:01 ` John Wood
2020-09-10 20:39 ` [RESEND][RFC PATCH 0/6] Fork brute force attack mitigation (fbfam) Jann Horn
2020-09-10 23:58 ` Kees Cook
[not found] ` <20200911144806.GA4128@ubuntu>
[not found] ` <202009120053.9FB7F2A7@keescook>
2020-09-12 12:24 ` John Wood
2020-09-12 0:03 ` James Morris
2020-09-12 7:56 ` Kees Cook
2020-09-12 9:36 ` John Wood
2020-09-12 14:47 ` Mel Gorman
2020-09-12 20:48 ` Ondrej Mosnacek
2020-09-13 7:24 ` John Wood
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