From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A68B3C433F5 for ; Fri, 15 Oct 2021 22:11:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 870146058D for ; Fri, 15 Oct 2021 22:11:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243306AbhJOWN4 (ORCPT ); Fri, 15 Oct 2021 18:13:56 -0400 Received: from out01.mta.xmission.com ([166.70.13.231]:41370 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243322AbhJOWNs (ORCPT ); Fri, 15 Oct 2021 18:13:48 -0400 Received: from in01.mta.xmission.com ([166.70.13.51]:44566) by out01.mta.xmission.com with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1mbVQR-002qU4-4e; Fri, 15 Oct 2021 16:11:39 -0600 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95]:47268 helo=email.xmission.com) by in01.mta.xmission.com with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1mbVQO-00Gjfh-QR; Fri, 15 Oct 2021 16:11:38 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: Rune Kleveland Cc: Yu Zhao , Alexey Gladkov , Jordan Glover , LKML , linux-mm@kvack.org, containers@lists.linux-foundation.org References: <1M9_d6wrcu6rdPe1ON0_k0lOxJMyyot3KAb1gdyuwzDPC777XVUWPHoTCEVmcK3fYfgu7sIo3PSaLe9KulUdm4TWVuqlbKyYGxRAjsf_Cpk=@protonmail.ch> <87ee9pa6xw.fsf@disp2133> <878rzw77i3.fsf@disp2133> <20210929173611.fo5traia77o63gpw@example.org> <20210930130640.wudkpmn3cmah2cjz@example.org> <878rz8wwb6.fsf@disp2133> <87v92cvhbf.fsf@disp2133> Date: Fri, 15 Oct 2021 17:10:58 -0500 In-Reply-To: (Rune Kleveland's message of "Sun, 10 Oct 2021 10:59:10 +0200") Message-ID: <87mtnavszx.fsf_-_@disp2133> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1mbVQO-00Gjfh-QR;;;mid=<87mtnavszx.fsf_-_@disp2133>;;;hst=in01.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX1/UyOiU0KmRrKw/e3bqzd52ydXHDbwubbA= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: [CFT][PATCH] ucounts: Fix signal ucount refcounting X-SA-Exim-Version: 4.2.1 (built Sat, 08 Feb 2020 21:53:50 +0000) X-SA-Exim-Scanned: Yes (on in01.mta.xmission.com) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org In commit fda31c50292a ("signal: avoid double atomic counter increments for user accounting") Linus made a clever optimization to how rlimits and the struct user_struct. Unfortunately that optimization does not work in the obvious way when moved to nested rlimits. The problem is that the last decrement of the per user namespace per user sigpending counter might also be the last decrement of the sigpending counter in the parent user namespace as well. Which means that simply freeing the leaf ucount in __free_sigqueue is not enough. Maintain the optimization and handle the tricky cases by introducing inc_rlimit_get_ucounts and dec_rlimit_put_ucounts. By moving the entire optimization into functions that perform all of the work it becomes possible to ensure that every level is handled properly. I wish we had a single user across all of the threads whose rlimit could be charged so we did not need this complexity. Cc: stable@vger.kernel.org Fixes: d64696905554 ("Reimplement RLIMIT_SIGPENDING on top of ucounts") Signed-off-by: "Eric W. Biederman" --- With a lot of help from Alex who found a way I could reproduce this I believe I have found the issue. Could people who are seeing this issue test and verify this solves the problem for them? include/linux/user_namespace.h | 2 ++ kernel/signal.c | 25 +++++---------------- kernel/ucount.c | 41 ++++++++++++++++++++++++++++++++++ 3 files changed, 49 insertions(+), 19 deletions(-) diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h index eb70cabe6e7f..33a4240e6a6f 100644 --- a/include/linux/user_namespace.h +++ b/include/linux/user_namespace.h @@ -127,6 +127,8 @@ static inline long get_ucounts_value(struct ucounts *ucounts, enum ucount_type t long inc_rlimit_ucounts(struct ucounts *ucounts, enum ucount_type type, long v); bool dec_rlimit_ucounts(struct ucounts *ucounts, enum ucount_type type, long v); +long inc_rlimit_get_ucounts(struct ucounts *ucounts, enum ucount_type type); +void dec_rlimit_put_ucounts(struct ucounts *ucounts, enum ucount_type type); bool is_ucounts_overlimit(struct ucounts *ucounts, enum ucount_type type, unsigned long max); static inline void set_rlimit_ucount_max(struct user_namespace *ns, diff --git a/kernel/signal.c b/kernel/signal.c index a3229add4455..762de58c6e76 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -425,22 +425,10 @@ __sigqueue_alloc(int sig, struct task_struct *t, gfp_t gfp_flags, */ rcu_read_lock(); ucounts = task_ucounts(t); - sigpending = inc_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_SIGPENDING, 1); - switch (sigpending) { - case 1: - if (likely(get_ucounts(ucounts))) - break; - fallthrough; - case LONG_MAX: - /* - * we need to decrease the ucount in the userns tree on any - * failure to avoid counts leaking. - */ - dec_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_SIGPENDING, 1); - rcu_read_unlock(); - return NULL; - } + sigpending = inc_rlimit_get_ucounts(ucounts, UCOUNT_RLIMIT_SIGPENDING); rcu_read_unlock(); + if (sigpending == LONG_MAX) + return NULL; if (override_rlimit || likely(sigpending <= task_rlimit(t, RLIMIT_SIGPENDING))) { q = kmem_cache_alloc(sigqueue_cachep, gfp_flags); @@ -449,8 +437,7 @@ __sigqueue_alloc(int sig, struct task_struct *t, gfp_t gfp_flags, } if (unlikely(q == NULL)) { - if (dec_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_SIGPENDING, 1)) - put_ucounts(ucounts); + dec_rlimit_put_ucounts(ucounts, UCOUNT_RLIMIT_SIGPENDING); } else { INIT_LIST_HEAD(&q->list); q->flags = sigqueue_flags; @@ -463,8 +450,8 @@ static void __sigqueue_free(struct sigqueue *q) { if (q->flags & SIGQUEUE_PREALLOC) return; - if (q->ucounts && dec_rlimit_ucounts(q->ucounts, UCOUNT_RLIMIT_SIGPENDING, 1)) { - put_ucounts(q->ucounts); + if (q->ucounts) { + dec_rlimit_put_ucounts(q->ucounts, UCOUNT_RLIMIT_SIGPENDING); q->ucounts = NULL; } kmem_cache_free(sigqueue_cachep, q); diff --git a/kernel/ucount.c b/kernel/ucount.c index 3b7e176cf7a2..687d77aa66bb 100644 --- a/kernel/ucount.c +++ b/kernel/ucount.c @@ -285,6 +285,47 @@ bool dec_rlimit_ucounts(struct ucounts *ucounts, enum ucount_type type, long v) return (new == 0); } +static void do_dec_rlimit_put_ucounts(struct ucounts *ucounts, + struct ucounts *last, enum ucount_type type) +{ + struct ucounts *iter; + for (iter = ucounts; iter != last; iter = iter->ns->ucounts) { + long dec = atomic_long_add_return(-1, &iter->ucount[type]); + WARN_ON_ONCE(dec < 0); + if (dec == 0) + put_ucounts(iter); + } +} + +void dec_rlimit_put_ucounts(struct ucounts *ucounts, enum ucount_type type) +{ + do_dec_rlimit_put_ucounts(ucounts, NULL, type); +} + +long inc_rlimit_get_ucounts(struct ucounts *ucounts, enum ucount_type type) +{ + struct ucounts *iter; + long dec, ret = 0; + + for (iter = ucounts; iter; iter = iter->ns->ucounts) { + long max = READ_ONCE(iter->ns->ucount_max[type]); + long new = atomic_long_add_return(1, &iter->ucount[type]); + if (new < 0 || new > max) + goto unwind; + else if (iter == ucounts) + ret = new; + if ((new == 1) && (get_ucounts(iter) != iter)) + goto dec_unwind; + } + return ret; +dec_unwind: + dec = atomic_long_add_return(1, &iter->ucount[type]); + WARN_ON_ONCE(dec < 0); +unwind: + do_dec_rlimit_put_ucounts(ucounts, iter, type); + return LONG_MAX; +} + bool is_ucounts_overlimit(struct ucounts *ucounts, enum ucount_type type, unsigned long max) { struct ucounts *iter; -- 2.20.1