From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp-fw-52002.amazon.com (smtp-fw-52002.amazon.com [52.119.213.150]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 20D9328F3; Tue, 13 May 2025 00:18:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=52.119.213.150 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747095490; cv=none; b=N5nTrhhNHQvkB0yv7CBVTk86wM6yxPAbKe996nxF1bMsiSwZ3Hz1HBlYslT6EjPvxMzzCotouFVzHYDvpTUZefZIydrgKVvk1gbWHUR4CfX6DwG9RcxkcJv4GGKSHSdUGqpR34f14WNklu8KSrv1INrMlBrNqPz1zNwVgxGWZnI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747095490; c=relaxed/simple; bh=SsVMbcIv3zVzCdAnix7sRxmHxtkf9TkXt3Sbd72U9PU=; h=From:To:CC:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=gmIa2iIUyKgcH3Apsb2GuRrZXde7iXu3VUrCj5JhI7cuAw2eaxhwMKMn1KbWi2uIq0GMPUdZzEJt6Hcm0Pf3LS4dC+ZYECLMDwmLqxkIyIMnhyqb2sqJ57Q2jGmqOqfRq3oafcfAZi8ZE6svJap0jvvn7vvu7A38nfLZXmjmU4U= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amazon.com; spf=pass smtp.mailfrom=amazon.co.jp; dkim=pass (2048-bit key) header.d=amazon.com header.i=@amazon.com header.b=edFefTng; arc=none smtp.client-ip=52.119.213.150 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amazon.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=amazon.co.jp Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=amazon.com header.i=@amazon.com header.b="edFefTng" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazoncorp2; t=1747095489; x=1778631489; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=J/O6pzhVKHaw/TXHTk58VZBH72gJWEpxM01lZaMwbpc=; b=edFefTngE3GVjt3Gvn/EwecX6DNgvS/RNO3GKrEXGlewaIotA6D2QRTq j4el3Ww4nxzlRquI3Vnk1wailzF/iQ0uvy8Q1PUGBDoZ2G1uVIjImFzza l3GPAutVtuvqjAGJAX7sy/QVWrT+6e1rYf3DQ8bnnnDCGWJdayZow2kmb 4JxBSd/ssgNq6LNli9UV+5KnOvHOLeBfet7IxSM92A6o4LBUJcBkG84Ao 84OReEEdJHTvSxjpk5RFqN5heimQZDSzWkTwukMjIwZ/L2gTqiMyBLuJ/ GT1sPLZjhh8MDIiGXHQwQgY+8Q3dLOXfJ5OtAyy6c1mw61ylVtGNAJt6d g==; X-IronPort-AV: E=Sophos;i="6.15,283,1739836800"; d="scan'208";a="722057387" Received: from iad12-co-svc-p1-lb1-vlan3.amazon.com (HELO smtpout.prod.us-west-2.prod.farcaster.email.amazon.dev) ([10.43.8.6]) by smtp-border-fw-52002.iad7.amazon.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 13 May 2025 00:18:04 +0000 Received: from EX19MTAUWC002.ant.amazon.com [10.0.21.151:64555] by smtpin.naws.us-west-2.prod.farcaster.email.amazon.dev [10.0.51.68:2525] with esmtp (Farcaster) id f44233c5-dd2b-4c7c-bdca-3a8a74545c69; Tue, 13 May 2025 00:18:03 +0000 (UTC) X-Farcaster-Flow-ID: f44233c5-dd2b-4c7c-bdca-3a8a74545c69 Received: from EX19D004ANA001.ant.amazon.com (10.37.240.138) by EX19MTAUWC002.ant.amazon.com (10.250.64.143) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.1544.14; Tue, 13 May 2025 00:18:03 +0000 Received: from 6c7e67bfbae3.amazon.com (10.187.170.42) by EX19D004ANA001.ant.amazon.com (10.37.240.138) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.1544.14; Tue, 13 May 2025 00:17:59 +0000 From: Kuniyuki Iwashima To: CC: , , , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH v6 4/9] coredump: add coredump socket Date: Mon, 12 May 2025 17:17:36 -0700 Message-ID: <20250513001751.71660-1-kuniyu@amazon.com> X-Mailer: git-send-email 2.49.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-ClientProxiedBy: EX19D046UWA002.ant.amazon.com (10.13.139.39) To EX19D004ANA001.ant.amazon.com (10.37.240.138) From: Luca Boccassi Date: Mon, 12 May 2025 11:58:54 +0100 > On Mon, 12 May 2025 at 09:56, Christian Brauner wrote: > > > > Coredumping currently supports two modes: > > > > (1) Dumping directly into a file somewhere on the filesystem. > > (2) Dumping into a pipe connected to a usermode helper process > > spawned as a child of the system_unbound_wq or kthreadd. > > > > For simplicity I'm mostly ignoring (1). There's probably still some > > users of (1) out there but processing coredumps in this way can be > > considered adventurous especially in the face of set*id binaries. > > > > The most common option should be (2) by now. It works by allowing > > userspace to put a string into /proc/sys/kernel/core_pattern like: > > > > |/usr/lib/systemd/systemd-coredump %P %u %g %s %t %c %h > > > > The "|" at the beginning indicates to the kernel that a pipe must be > > used. The path following the pipe indicator is a path to a binary that > > will be spawned as a usermode helper process. Any additional parameters > > pass information about the task that is generating the coredump to the > > binary that processes the coredump. > > > > In the example core_pattern shown above systemd-coredump is spawned as a > > usermode helper. There's various conceptual consequences of this > > (non-exhaustive list): > > > > - systemd-coredump is spawned with file descriptor number 0 (stdin) > > connected to the read-end of the pipe. All other file descriptors are > > closed. That specifically includes 1 (stdout) and 2 (stderr). This has > > already caused bugs because userspace assumed that this cannot happen > > (Whether or not this is a sane assumption is irrelevant.). > > > > - systemd-coredump will be spawned as a child of system_unbound_wq. So > > it is not a child of any userspace process and specifically not a > > child of PID 1. It cannot be waited upon and is in a weird hybrid > > upcall which are difficult for userspace to control correctly. > > > > - systemd-coredump is spawned with full kernel privileges. This > > necessitates all kinds of weird privilege dropping excercises in > > userspace to make this safe. > > > > - A new usermode helper has to be spawned for each crashing process. > > > > This series adds a new mode: > > > > (3) Dumping into an abstract AF_UNIX socket. > > > > Userspace can set /proc/sys/kernel/core_pattern to: > > > > @address SO_COOKIE > > > > The "@" at the beginning indicates to the kernel that the abstract > > AF_UNIX coredump socket will be used to process coredumps. The address > > is given by @address and must be followed by the socket cookie of the > > coredump listening socket. > > > > The socket cookie is used to verify the socket connection. If the > > coredump server restarts or crashes and someone recycles the socket > > address the kernel will detect that the address has been recycled as the > > socket cookie will have necessarily changed and refuse to connect. > > This dynamic/cookie prefix makes it impossible to use this with socket > activation units. The way systemd-coredump works is that every > instance is an independent templated unit, spawned when there's a > connection to the private socket. If the path was fixed, we could just > reuse the same mechanism, it would fit very nicely with minimal > changes. Note this version does not use prefix. Now it requires users to just pass the socket cookie via core_pattern so that the kernel can verify the peer. > > But because you need a "server" to be permanently running, this means > socket-based activation can no longer work, and systemd-coredump must > switch to a persistently-running mode. The only thing for systemd to do is assign a cookie after socket creation. As long as systemd hold the file descriptor of the socket, you don't need a dedicated "server" running permanently, and the fd can be passed around to a spawned/activated process. > This is a severe degradation of > functionality, will continuously waste CPU/memory resources for no > good reasons, and makes the whole thing more fragile and complex, as > if there are any issues with this server, you start losing core files. > And honestly I don't really see the point? Setting the pattern is a > privileged operation anyway. systemd manages the socket with a socket > unit and again that's privileged already. > > Could we drop this cookie prefix and go back to the previous version > (v5), please? Or if there is some specific non-systemd use case in > mind that I am not aware of, have both options, so that we can use the > simpler and more straightforward one with systemd-coredump.