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 8EB70C433F5 for ; Sat, 2 Apr 2022 21:16:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239719AbiDBVRx (ORCPT ); Sat, 2 Apr 2022 17:17:53 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43878 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236281AbiDBVRs (ORCPT ); Sat, 2 Apr 2022 17:17:48 -0400 Received: from mail-wr1-x436.google.com (mail-wr1-x436.google.com [IPv6:2a00:1450:4864:20::436]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C94861CB24 for ; Sat, 2 Apr 2022 14:15:55 -0700 (PDT) Received: by mail-wr1-x436.google.com with SMTP id m30so8968937wrb.1 for ; Sat, 02 Apr 2022 14:15:55 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=message-id:date:mime-version:user-agent:subject:content-language:to :references:cc:from:in-reply-to:content-transfer-encoding; bh=PRT8NrovPsISh5Psd6i6W0q2XevnObDjaAcnqujaODE=; b=XAeOYVHWOlUB7qIKxjWjAuZXvYTZbcJcqT2j/X8qYMY6BcixoSxSWa4GKdRdSEnK5b L7ePvvCclWVLc/LayzbzCI1vUo1rp3whwWUkUa1aOtJVAzIyHXvM18NW2/W4iYTsb0Nv fEfRlIIEoteXfRdRpeOGdDJy79sm+CqRBMb4v1QP4s0GmAsfG6jt4onPGSVW3Fh37+o4 UqFgLOMeFky4upkJ+cBZRjg1L9wHzkDujeZAmWC7OBsx1fUPWA5cgCwfDs4z8C11cCJh hvvxMMt7eVQvkeROBhSUnGy/no92p/HmK/Lo3YWqE3V4zVNcbxsdvH/9ybXE/fRaxsl5 icYA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:message-id:date:mime-version:user-agent:subject :content-language:to:references:cc:from:in-reply-to :content-transfer-encoding; bh=PRT8NrovPsISh5Psd6i6W0q2XevnObDjaAcnqujaODE=; b=pM+QoVHC3K4tcMqwfqA0/vRK1i3iP8zJZWzM+mZMJLMrQFkwnTTUUrM0U/M00iTVJL GQCrTaHfppQg5RdISj8u5/NNsI6Gwb+tj6jv/zG1eUlsman5noQoys91H8eSJRCnq74u 5+hth24+vw6CV08/VBb/b2g721OtZ/5rDINnuXNR8+7NTm7eMo/pXea5XNiEG2jgbtoq vKu/j4DtFn8DQN3gsT3q5EqrSdF0earKr8DUMGaoj9GpTb2W+l2J4Gm7HkM62tplRpRs 8CT0Nfrq2Y37hKCDMrcmWwmsMOgbnkvP5nQFAz/Sg5yGcQHmVV1CKq598xfpCPXwpSTF 5RKA== X-Gm-Message-State: AOAM533P4eRXjArngbchy5jR5yWM9oR5KcXlZwyUoZtiR+cOA8YtKF1b wd9+vArnuERtOK4yVLmpukw= X-Google-Smtp-Source: ABdhPJwWlcEjr8rpBe7FQKRJtsrRdQInIy4ePZdtG2FoMNXjMjRdRthVRBorVkqeRzMK1sIcCG6/vw== X-Received: by 2002:a05:6000:18a2:b0:203:d2f5:28a0 with SMTP id b2-20020a05600018a200b00203d2f528a0mr12370963wri.355.1648934154224; Sat, 02 Apr 2022 14:15:54 -0700 (PDT) Received: from [192.168.0.160] ([170.253.36.171]) by smtp.gmail.com with ESMTPSA id a2-20020a5d53c2000000b0020604b2667asm3446507wrw.81.2022.04.02.14.15.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 02 Apr 2022 14:15:53 -0700 (PDT) Message-ID: <4fb02f5f-60f9-42af-ddd5-fe5af877231f@gmail.com> Date: Sat, 2 Apr 2022 23:15:52 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.7.0 Subject: vfork(2) fails after unshare(CLONE_NEWTIME) (was: [Bug 215769] man 2 vfork() does not document corner case when PID == 1) Content-Language: en-US To: bugzilla-daemon@kernel.org, "linux-kernel@vger.kernel.org" , =?UTF-8?B?0JrQvtGA0LXQvdCx0LXRgNCzINCc0LDRgNC6?= , Christian Brauner References: Cc: Andrei Vagin , Dmitry Safonov , Thomas Gleixner , Arnd Bergmann , Serge Hallyn From: "Alejandro Colomar (man-pages)" In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org [Added some kernel CCs that may know what's going on] Hi, On 3/31/22 09:53, bugzilla-daemon@kernel.org wrote: > https://bugzilla.kernel.org/show_bug.cgi?id=215769 > > --- Comment #3 from Коренберг Марк (socketpair@gmail.com) --- > Hi, > I appreciate depth of information validation. Actually, you are right. vfork() > DOES work with pid=1 processes. I figured out the cause in my case. In order to > reproduce -- add unshare(CLONE_NEWTIME) just before vfork(). Now, I don't know > if it's a bug in vfork() or in fork(). Yes, both are clone() actually. > > In any case, they should either both give EINVAL or both don't fail. But it's > definitely bug in the kernel around CLONE_NEWTIME. > On 3/31/22 10:12, bugzilla-daemon@kernel.org wrote: > https://bugzilla.kernel.org/show_bug.cgi?id=215769 > > --- Comment #4 from Коренберг Марк (socketpair@gmail.com) --- > #define _GNU_SOURCE 1 > #include > #include > #include > #include > #include > #include > #include > > #ifndef CLONE_NEWTIME > #define CLONE_NEWTIME 0x00000080 > #endif > > int main (void) > { > if (unshare (CLONE_NEWTIME)) err (EXIT_FAILURE, "UNSHARE_NEWTIME"); > > pid_t pid; > switch (pid=vfork ()) > { > case 0: > _exit(0); > case -1: > err(EXIT_FAILURE, "vfork BUG"); > default: > waitpid(pid, NULL, 0); > } > return 0; > } > I could reproduce it with the following code. I tried syscall(SYS_vfork) to make sure it's not a problem in the libc wrapper, and to make sure I do call vfork(2). If I replace vfork(2) with fork(2), I don't get the error. $ cat vfork.c #define _GNU_SOURCE #include #include #include #include #include #include #include int main(void) { pid_t pid; if (unshare(CLONE_NEWTIME) == -1) err(EXIT_FAILURE, "unshare(2)"); if (signal(SIGCHLD, SIG_IGN) == SIG_ERR) err(EXIT_FAILURE, "sigaction(2)"); pid = syscall(SYS_vfork); switch (pid) { case 0: errx(EXIT_SUCCESS, "Grandchild exiting normally."); case -1: /* If we got here, the report is confirmed. */ err(EXIT_FAILURE, "vfork(2)"); default: errx(EXIT_SUCCESS, "Child exiting normally."); } } $ cc -Wall -Wextra -Werror vfork.c $ sudo ./a.out a.out: vfork(2): Invalid argument $ grep_syscall_def vfork kernel/fork.c:2711: SYSCALL_DEFINE0(vfork) { struct kernel_clone_args args = { .flags = CLONE_VFORK | CLONE_VM, .exit_signal = SIGCHLD, }; return kernel_clone(&args); } Maybe someone in the kernel can send some patch for the clone(2) and/or vfork(2) manual pages that explains the reason (if it's intended). Thanks, Alex -- Alejandro Colomar Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/ http://www.alejandro-colomar.es/