From patchwork Sun Feb 21 15:49:16 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: John Wood X-Patchwork-Id: 12097585 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0C7C2C433E6 for ; Sun, 21 Feb 2021 18:38:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CE16064EEF for ; Sun, 21 Feb 2021 18:38:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230158AbhBUSiw (ORCPT ); Sun, 21 Feb 2021 13:38:52 -0500 Received: from mout.gmx.net ([212.227.17.22]:38985 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230088AbhBUSiv (ORCPT ); Sun, 21 Feb 2021 13:38:51 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gmx.net; s=badeba3b8450; t=1613932620; bh=SlIggBd+WqRJccgKoSY+jsgMPGho7MOSNDrdTCHcJIE=; h=X-UI-Sender-Class:From:To:Cc:Subject:Date:In-Reply-To:References; b=JSnUXw2WWYy/DcBcBvxf/eck/peQmc+Fc1fB5o+3gPF41xLs0gwYV+iNV6rUbyUlC yEkqL6t1uAMZrY/8GxV5dIA77bU0VRqkMZDRHwtSUnC2bobeLRVNF+ArmmXGUeJvoV qMU2xhfSMe+3QMQKi5REclkK4rtajjBtRptizwZk= X-UI-Sender-Class: 01bb95c1-4bf8-414a-932a-4f6e2808ef9c Received: from localhost.localdomain ([83.52.229.153]) by mail.gmx.net (mrgmx104 [212.227.17.174]) with ESMTPSA (Nemesis) id 1MQvD5-1lS0sO3gRz-00NyX8; Sun, 21 Feb 2021 19:37:00 +0100 From: John Wood To: Kees Cook , Jann Horn , Randy Dunlap , Jonathan Corbet , James Morris , Shuah Khan Cc: John Wood , "Serge E. Hallyn" , Greg Kroah-Hartman , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [PATCH v3 5/8] security/brute: Mitigate a brute force attack Date: Sun, 21 Feb 2021 16:49:16 +0100 Message-Id: <20210221154919.68050-6-john.wood@gmx.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210221154919.68050-1-john.wood@gmx.com> References: <20210221154919.68050-1-john.wood@gmx.com> MIME-Version: 1.0 X-Provags-ID: V03:K1:UPdUC4a8CRZEE5wqJf0baxsrqjeCTJQ5IRIHSh41m/k51iqL/UV TNftC3ZL3GMVW3AMkaO74Msv+MJHrIxfPoePdQ07ujLmm3w2THpFJXsyR/BShj589SZbV3f ZenPq+NKddx/+ukYG/5ZCcpnMgiIqSbMWKfLkflS1HXDfA/ITxIhF5Iwyy0/LuPoplsmH1i YHsG7FF4rVjmJauyxWI8g== X-UI-Out-Filterresults: notjunk:1;V03:K0:/COfCpmUkGI=:TDb8v4wPPri8+NAYVVpP9V 5SNAtp5VnfkbCzavNXd9GRuDpX4wVOxFBCq1w1UKQ5ca7+ZUOKAA5zVF40h9M7QL3/1VqNJIU nEaBJnZhnJl8JHRWEIUArL4DQ8O1n9F4prk2GxQJYT0iY5AVqoQSv7tmI0sb/BDarbX+2XTnD TQH94UEIRc+h3BXszdMCC4WZm+w2QV7uCvwre2I4p0D7+looHaVXilzHSJ8Qp5oCAfrRz4V4I YgVe9aCIFWhpPA8e3FVCJR2FsZqXzUgF9QwILNR30CxpJ11jM+kluTUHlFdnomdyrPilV5Eqw ok0A6jiOKwZI+g6Kzg5Bq2ciDIKzaundOx8NPNMGntX3pFw4YerbrI8F7gLbi6yUmLVu8qkn6 BOP4VoVbCsTqSHOiRHFCGf11jviWZhrXMPz41gDdshM1JggEw/+AcFyTSM25aKeJsst1+lUF1 +ThWXXbVrKBqpPyWLSFGhxRyLOMlTCVqNFnqhrkKVnKMCoOOOPGe6q3yMvlPYCrponccUrzBc H5u9RKnrawPnzgWgwgzvr/xYPtZtbNmDJ+hooiGCKvw1hhVWRMXBSRqcs2kVCBDKs/fvISSQl XID8JF0jXGCTpsvKy4kPU7XFFgM7Sv9YUcXuZmTMgdiPd5/2Khs5nPW/jSx9udLInAv0E1O6T 71n0VrEWPUvimEnpVMgXqEwf8Oac/VqB7VfayS23qGbXcBHPsnR207l70XJ17APg4RgF/owYb KyP78S3e3kkoPT563Q3nHe5VfCJ7U21//c7BEJlgUTfEUoLFibudAilByxoB1C2nQnYGIe1zf mpx3SnsqK9+3FzgwpRXk6VXY8QUACLJy3t2nMb67EG1ueFvQ14r7kbVP99AQwGwpxmet1wy7d VcLnpD9EUZpVaZdOHwOw== Precedence: bulk List-ID: In order to mitigate a brute force attack all the offending tasks involved in the attack must be killed. In other words, it is necessary to kill all the tasks that share the fork and/or exec statistical data related to the attack. Moreover, if the attack happens through the fork system call, the processes that have the same group_leader that the current task (the task that has crashed) must be avoided since they are in the path to be killed. When the SIGKILL signal is sent to the offending tasks, the function "brute_kill_offending_tasks" will be called in a recursive way from the task_fatal_signal LSM hook due to a small crash period. So, to avoid kill again the same tasks due to a recursive call of this function, it is necessary to disable the attack detection for the involved hierarchies. To disable the attack detection, set to zero the last crash timestamp and avoid to compute the application crash period in this case. Signed-off-by: John Wood --- security/brute/brute.c | 141 ++++++++++++++++++++++++++++++++++++++--- 1 file changed, 132 insertions(+), 9 deletions(-) -- 2.25.1 diff --git a/security/brute/brute.c b/security/brute/brute.c index 8d03ea0ecac5..581aba291438 100644 --- a/security/brute/brute.c +++ b/security/brute/brute.c @@ -22,6 +22,7 @@ #include #include #include +#include #include #include #include @@ -64,7 +65,7 @@ struct brute_cred { * @lock: Lock to protect the brute_stats structure. * @refc: Reference counter. * @faults: Number of crashes. - * @jiffies: Last crash timestamp. + * @jiffies: Last crash timestamp. If zero, the attack detection is disabled. * @period: Crash period's moving average. * @saved_cred: Saved credentials. * @network: Network activity flag. @@ -566,6 +567,125 @@ static inline void print_fork_attack_running(void) pr_warn("Fork brute force attack detected [%s]\n", current->comm); } +/** + * brute_disabled() - Test if the brute force attack detection is disabled. + * @stats: Statistical data shared by all the fork hierarchy processes. + * + * The brute force attack detection enabling/disabling is based on the last + * crash timestamp. A zero timestamp indicates that this feature is disabled. A + * timestamp greater than zero indicates that the attack detection is enabled. + * + * The statistical data shared by all the fork hierarchy processes cannot be + * NULL. + * + * It's mandatory to disable interrupts before acquiring the brute_stats::lock + * since the task_free hook can be called from an IRQ context during the + * execution of the task_fatal_signal hook. + * + * Context: Must be called with interrupts disabled and brute_stats_ptr_lock + * held. + * Return: True if the brute force attack detection is disabled. False + * otherwise. + */ +static bool brute_disabled(struct brute_stats *stats) +{ + bool disabled; + + spin_lock(&stats->lock); + disabled = !stats->jiffies; + spin_unlock(&stats->lock); + + return disabled; +} + +/** + * brute_disable() - Disable the brute force attack detection. + * @stats: Statistical data shared by all the fork hierarchy processes. + * + * To disable the brute force attack detection it is only necessary to set the + * last crash timestamp to zero. A zero timestamp indicates that this feature is + * disabled. A timestamp greater than zero indicates that the attack detection + * is enabled. + * + * The statistical data shared by all the fork hierarchy processes cannot be + * NULL. + * + * Context: Must be called with interrupts disabled and brute_stats_ptr_lock + * and brute_stats::lock held. + */ +static inline void brute_disable(struct brute_stats *stats) +{ + stats->jiffies = 0; +} + +/** + * enum brute_attack_type - Brute force attack type. + * @BRUTE_ATTACK_TYPE_FORK: Attack that happens through the fork system call. + * @BRUTE_ATTACK_TYPE_EXEC: Attack that happens through the execve system call. + */ +enum brute_attack_type { + BRUTE_ATTACK_TYPE_FORK, + BRUTE_ATTACK_TYPE_EXEC, +}; + +/** + * brute_kill_offending_tasks() - Kill the offending tasks. + * @attack_type: Brute force attack type. + * @stats: Statistical data shared by all the fork hierarchy processes. + * + * When a brute force attack is detected all the offending tasks involved in the + * attack must be killed. In other words, it is necessary to kill all the tasks + * that share the same statistical data. Moreover, if the attack happens through + * the fork system call, the processes that have the same group_leader that the + * current task must be avoided since they are in the path to be killed. + * + * When the SIGKILL signal is sent to the offending tasks, this function will be + * called again from the task_fatal_signal hook due to a small crash period. So, + * to avoid kill again the same tasks due to a recursive call of this function, + * it is necessary to disable the attack detection for this fork hierarchy. + * + * The statistical data shared by all the fork hierarchy processes cannot be + * NULL. + * + * It's mandatory to disable interrupts before acquiring the brute_stats::lock + * since the task_free hook can be called from an IRQ context during the + * execution of the task_fatal_signal hook. + * + * Context: Must be called with interrupts disabled and tasklist_lock and + * brute_stats_ptr_lock held. + */ +static void brute_kill_offending_tasks(enum brute_attack_type attack_type, + struct brute_stats *stats) +{ + struct task_struct *p; + struct brute_stats **p_stats; + + spin_lock(&stats->lock); + + if (attack_type == BRUTE_ATTACK_TYPE_FORK && + refcount_read(&stats->refc) == 1) { + spin_unlock(&stats->lock); + return; + } + + brute_disable(stats); + spin_unlock(&stats->lock); + + for_each_process(p) { + if (attack_type == BRUTE_ATTACK_TYPE_FORK && + p->group_leader == current->group_leader) + continue; + + p_stats = brute_stats_ptr(p); + if (*p_stats != stats) + continue; + + do_send_sig_info(SIGKILL, SEND_SIG_PRIV, p, PIDTYPE_PID); + pr_warn_ratelimited("Offending process %d [%s] killed\n", + p->pid, p->comm); + } +} + /** * brute_manage_fork_attack() - Manage a fork brute force attack. * @stats: Statistical data shared by all the fork hierarchy processes. @@ -581,8 +701,8 @@ static inline void print_fork_attack_running(void) * since the task_free hook can be called from an IRQ context during the * execution of the task_fatal_signal hook. * - * Context: Must be called with interrupts disabled and brute_stats_ptr_lock - * held. + * Context: Must be called with interrupts disabled and tasklist_lock and + * brute_stats_ptr_lock held. * Return: The last crash timestamp before updating it. */ static u64 brute_manage_fork_attack(struct brute_stats *stats, u64 now) @@ -590,8 +710,10 @@ static u64 brute_manage_fork_attack(struct brute_stats *stats, u64 now) u64 last_fork_crash; last_fork_crash = brute_update_crash_period(stats, now); - if (brute_attack_running(stats)) + if (brute_attack_running(stats)) { print_fork_attack_running(); + brute_kill_offending_tasks(BRUTE_ATTACK_TYPE_FORK, stats); + } return last_fork_crash; } @@ -778,8 +900,10 @@ static void brute_manage_exec_attack(struct brute_stats *stats, u64 now, if (fork_period == exec_period) return; - if (brute_attack_running(exec_stats)) + if (brute_attack_running(exec_stats)) { print_exec_attack_running(exec_stats); + brute_kill_offending_tasks(BRUTE_ATTACK_TYPE_EXEC, exec_stats); + } } /** @@ -895,10 +1019,9 @@ static void brute_task_fatal_signal(const kernel_siginfo_t *siginfo) read_lock(&tasklist_lock); read_lock_irqsave(&brute_stats_ptr_lock, flags); - if (WARN(!*stats, "No statistical data\n")) - goto unlock; - - if (!brute_threat_model_supported(siginfo, *stats)) + if (WARN(!*stats, "No statistical data\n") || + brute_disabled(*stats) || + !brute_threat_model_supported(siginfo, *stats)) goto unlock; last_fork_crash = brute_manage_fork_attack(*stats, now);