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 E9F08C433EF for ; Mon, 18 Oct 2021 16:06:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C397D60FC2 for ; Mon, 18 Oct 2021 16:06:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232806AbhJRQJG (ORCPT ); Mon, 18 Oct 2021 12:09:06 -0400 Received: from out03.mta.xmission.com ([166.70.13.233]:33454 "EHLO out03.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229634AbhJRQJE (ORCPT ); Mon, 18 Oct 2021 12:09:04 -0400 Received: from in02.mta.xmission.com ([166.70.13.52]:59168) by out03.mta.xmission.com with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1mcVA3-00EDJj-RO; Mon, 18 Oct 2021 10:06:51 -0600 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95]:42518 helo=email.xmission.com) by in02.mta.xmission.com with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1mcVA2-00D6IZ-IN; Mon, 18 Oct 2021 10:06:51 -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, Hillf Danton 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> <87mtnavszx.fsf_-_@disp2133> Date: Mon, 18 Oct 2021 11:06:43 -0500 In-Reply-To: <87mtnavszx.fsf_-_@disp2133> (Eric W. Biederman's message of "Fri, 15 Oct 2021 17:10:58 -0500") Message-ID: <87fssytizw.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=1mcVA2-00D6IZ-IN;;;mid=<87fssytizw.fsf_-_@disp2133>;;;hst=in02.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX18lOS2RhPYdr9TbNbhkR5E8AaClnBvyS5I= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: [PATCH v2] 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 in02.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. The new function inc_rlimit_get_ucounts returns 0 on failure to increment the ucount. This is different than inc_rlimit_ucounts which increments the ucounts and returns LONG_MAX if the ucount counter has exceeded it's maximum or it wrapped (to indicate the counter needs to decremented). I wish we had a single user to account all pending signals to across all of the threads of a process so this complexity was not necessary Cc: stable@vger.kernel.org Fixes: d64696905554 ("Reimplement RLIMIT_SIGPENDING on top of ucounts") v1: https://lkml.kernel.org/r/87mtnavszx.fsf_-_@disp2133 Tested-by: Rune Kleveland Tested-by: Yu Zhao Tested-by: Jordan Glover Signed-off-by: "Eric W. Biederman" --- This is my version of the fix with all of the feedback rolled in. I have tested it and believe this is ready to send out. If folks code take a once over and see if I have spotted things. For the people who are testing or have tested this I have added your tested-by's please let me know if you mind. Eric include/linux/user_namespace.h | 2 ++ kernel/signal.c | 25 +++++------------ kernel/ucount.c | 49 ++++++++++++++++++++++++++++++++++ 3 files changed, 57 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..13d2505a14a0 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) + 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 bb51849e6375..eb03f3c68375 100644 --- a/kernel/ucount.c +++ b/kernel/ucount.c @@ -284,6 +284,55 @@ 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, *next; + for (iter = ucounts; iter != last; iter = next) { + long dec = atomic_long_add_return(-1, &iter->ucount[type]); + WARN_ON_ONCE(dec < 0); + next = iter->ns->ucounts; + 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) +{ + /* Caller must hold a reference to ucounts */ + 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; + if (iter == ucounts) + ret = new; + /* + * Grab an extra ucount reference for the caller when + * the rlimit count was previously 0. + */ + if (new != 1) + continue; + if (!get_ucounts(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 0; +} + bool is_ucounts_overlimit(struct ucounts *ucounts, enum ucount_type type, unsigned long max) { struct ucounts *iter; -- 2.20.1