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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 44455C433EF for ; Fri, 11 Feb 2022 18:32:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240176AbiBKScM (ORCPT ); Fri, 11 Feb 2022 13:32:12 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:39974 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242655AbiBKScK (ORCPT ); Fri, 11 Feb 2022 13:32:10 -0500 Received: from mail-il1-x136.google.com (mail-il1-x136.google.com [IPv6:2607:f8b0:4864:20::136]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8E69D2C9 for ; Fri, 11 Feb 2022 10:32:08 -0800 (PST) Received: by mail-il1-x136.google.com with SMTP id m8so7522199ilg.7 for ; Fri, 11 Feb 2022 10:32:08 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=google; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=hR0BNaskgNQ2rEDEEGiZfn+Qbe1DLRpQ6GavJuM1OP8=; b=dFxKY8uynIlFayqwyn6IlICvauejaukqN8D68uw5nNkmD9+SNZu16EO8U6XC7wv412 i/q5kwSRNGXCLqUkcAWumgWM3bNWLgjugW2dvS+OKzk1l05jnyBv1F82IWhj8IqnavdU bJ/Ak246KOcbC7J+dFGNY2rIBZIxfZOnVAkpU= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=hR0BNaskgNQ2rEDEEGiZfn+Qbe1DLRpQ6GavJuM1OP8=; b=I5cY4hBDonkMRh2mJ04Xrpzt7Yp6Xy7Hrcur/rOGg8ZvktiJ5ANzjmKiEDyP8+vObh VsFcG5N1kBpOSRuagynAqCsEn2iv49QzRMWVh2MLHE2YZAL/tm1Y04MWDtEGM4inoMVU SYEeP1CsHq6AuC+XWyuMQ7RvZVd9vP4yiQVjrtHo4d8V4tEldO0IXuJv/je/lViT7YGJ EdKyY4f4Ic8NCr2/Dfoj2x9JczFn4yDNEvaugcfHDdGG0DUtBRF1VP75MDmLjovgPc45 wM2z/etpwU7vkJ9GRmqTuYM/DjqL0citVCks1fTdFXEg7mkqMKN5vLoP1mxGgRVXA/ky lKpQ== X-Gm-Message-State: AOAM533XODnFa27o9ML/OojhshR2b9NBvE7wPw9AFkCAhxA+INvTn3UP GOpgZ8AOhdlN0oRwuq5uR9/p+g== X-Google-Smtp-Source: ABdhPJyckP23f2ZCgS5vZ2HOrMzLpFaw6fUVynBg7qm1D+pnwiRiF7ejIv1ZASLc7CZwzvDCjnbGfg== X-Received: by 2002:a05:6e02:1c41:: with SMTP id d1mr1562233ilg.88.1644604327941; Fri, 11 Feb 2022 10:32:07 -0800 (PST) Received: from [192.168.1.128] ([71.205.29.0]) by smtp.gmail.com with ESMTPSA id 193sm5542743iob.17.2022.02.11.10.32.07 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 11 Feb 2022 10:32:07 -0800 (PST) Subject: Re: [PATCH 6/8] ucounts: Handle inc_rlimit_ucounts wrapping in fork To: "Eric W. Biederman" , Alexey Gladkov Cc: linux-kernel@vger.kernel.org, Kees Cook , Shuah Khan , Christian Brauner , Solar Designer , Ran Xiaokai , containers@lists.linux-foundation.org, =?UTF-8?Q?Michal_Koutn=c3=bd?= , Shuah Khan References: <87o83e2mbu.fsf@email.froward.int.ebiederm.org> <20220211021324.4116773-6-ebiederm@xmission.com> <20220211113454.socmlrne5heux7q7@example.org> <87sfspz409.fsf@email.froward.int.ebiederm.org> From: Shuah Khan Message-ID: <85eb952b-4bff-73fb-caaa-bf49d6b16248@linuxfoundation.org> Date: Fri, 11 Feb 2022 11:32:06 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <87sfspz409.fsf@email.froward.int.ebiederm.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2/11/22 10:50 AM, Eric W. Biederman wrote: > Alexey Gladkov writes: > >> On Thu, Feb 10, 2022 at 08:13:22PM -0600, Eric W. Biederman wrote: >>> Move inc_rlimit_ucounts from copy_creds into copy_process immediately >>> after copy_creds where it can be called exactly once. Test for and >>> handle it when inc_rlimit_ucounts returns LONG_MAX indicating the >>> count has wrapped. >>> >>> This is good hygenine and fixes a theoretical bug. In practice >>> PID_MAX_LIMIT is at most 2^22 so there is not a chance the number of >>> processes would ever wrap even on an architecture with a 32bit long. >>> >>> Fixes: 21d1c5e386bc ("Reimplement RLIMIT_NPROC on top of ucounts") >>> Signed-off-by: "Eric W. Biederman" >>> --- >>> kernel/cred.c | 2 -- >>> kernel/fork.c | 2 ++ >>> 2 files changed, 2 insertions(+), 2 deletions(-) >>> >>> diff --git a/kernel/cred.c b/kernel/cred.c >>> index 229cff081167..96d5fd6ff26f 100644 >>> --- a/kernel/cred.c >>> +++ b/kernel/cred.c >>> @@ -358,7 +358,6 @@ int copy_creds(struct task_struct *p, unsigned long clone_flags) >>> kdebug("share_creds(%p{%d,%d})", >>> p->cred, atomic_read(&p->cred->usage), >>> read_cred_subscribers(p->cred)); >>> - inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1); >>> return 0; >>> } >>> >>> @@ -395,7 +394,6 @@ int copy_creds(struct task_struct *p, unsigned long clone_flags) >>> #endif >>> >>> p->cred = p->real_cred = get_cred(new); >>> - inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1); >>> alter_cred_subscribers(new, 2); >>> validate_creds(new); >>> return 0; >>> diff --git a/kernel/fork.c b/kernel/fork.c >>> index 6f62d37f3650..69333078259c 100644 >>> --- a/kernel/fork.c >>> +++ b/kernel/fork.c >>> @@ -2026,6 +2026,8 @@ static __latent_entropy struct task_struct *copy_process( >>> goto bad_fork_free; >>> >>> retval = -EAGAIN; >>> + if (inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1) == LONG_MAX) >>> + goto bad_fork_cleanup_count; >>> if (is_ucounts_overlimit(task_ucounts(p), UCOUNT_RLIMIT_NPROC, rlimit(RLIMIT_NPROC))) { >>> if ((task_ucounts(p) != &init_ucounts) && >>> !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN)) >> >> It might make sense to do something like: >> >> if (inc_rlimit_ucounts_overlimit(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1, rlimit(RLIMIT_NPROC)) == LONG_MAX) { >> if ((task_ucounts(p) != &init_ucounts) && >> !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN)) >> >> and the new function: >> >> long inc_rlimit_ucounts_overlimit(struct ucounts *ucounts, enum ucount_type type, long v, unsigned long rlimit) >> { >> struct ucounts *iter; >> long ret = 0; >> long max = rlimit; >> if (rlimit > LONG_MAX) >> max = LONG_MAX; >> for (iter = ucounts; iter; iter = iter->ns->ucounts) { >> long new = atomic_long_add_return(v, &iter->ucount[type]); >> if (new < 0 || new > max) >> ret = LONG_MAX; >> else if (iter == ucounts) >> ret = new; >> max = READ_ONCE(iter->ns->ucount_max[type]); >> } >> return ret; >> } >> >> This will avoid double checking the same userns tree. >> >> Or even modify inc_rlimit_ucounts. This function is used elsewhere like >> this: >> >> >> msgqueue = inc_rlimit_ucounts(info->ucounts, UCOUNT_RLIMIT_MSGQUEUE, mq_bytes); >> if (msgqueue == LONG_MAX || msgqueue > rlimit(RLIMIT_MSGQUEUE)) { >> >> >> memlock = inc_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_MEMLOCK, locked); >> if (!allowed && (memlock == LONG_MAX || memlock > lock_limit) && !capable(CAP_IPC_LOCK)) { >> >> >> In all cases, we have max value for comparison. > > Good point. The downside is that it means we can't use the same code > in exec. The upside is that the code is more idiomatic. > Checking on this a bit more on other callers of inc_rlimit_ucounts(), we might have another issue: 1. mqueue_get_inode() does: spin_lock(&mq_lock); msgqueue = inc_rlimit_ucounts(info->ucounts, UCOUNT_RLIMIT_MSGQUEUE, mq_bytes); if (msgqueue == LONG_MAX || msgqueue > rlimit(RLIMIT_MSGQUEUE)) { dec_rlimit_ucounts(info->ucounts, UCOUNT_RLIMIT_MSGQUEUE, mq_bytes); spin_unlock(&mq_lock); 2. user_shm_lock() &shmlock_user_lock spin_lock(&shmlock_user_lock); memlock = inc_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_MEMLOCK, locked); if (!allowed && (memlock == LONG_MAX || memlock > lock_limit) && !capable(CAP_IPC_LOCK)) { dec_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_MEMLOCK, locked); 3. user_namespace_sysctl_init() Doesn't check for max value. 4. copy_creds() doesn't check for max value in its 3 calls to inc_rlimit_ucounts() You can see that each of these instances some callers dec_rlimit_ucounts(). They hold different locks. So do we have a window where LONG_MAX could overflow and go unnoticed? thanks, -- Shuah