From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 18CC425CC5F; Mon, 5 May 2025 14:56:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746456971; cv=none; b=gLyJJD1lD+/2kc8XrlXg+CtTbNsPbcLo6vMdMqOsjn5d8F4cdb6w/khFVNBaHZ5eXJ0IWIHykNAVp/mx/eL/eMxArrFO+7obKwxsJPam9Mjv3RUYaWkUwyfEhp02cM2GdoWhmCfF8+6giE9wLBedZOxYbpcwzCu0ZD0tLfOhwSU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746456971; c=relaxed/simple; bh=bJ1ZR3VtEee2Lfg/kc3hGzfdhOtsDj5T36f80c1czIU=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=LrhsoYBTc370mRN4wWCJckuwBftxFyGrd88pGmv1fkjV7cnY6u4ozVga9tRcFcpv+fkgxcc8zpjbdOFkWlKr0nTyt7xZxQDinkZ9eLNVV/ELGqPtlyDLpsKApyiljziP0doZGTdFYn56Xrgkj8b8q/0c/vld5Ps/PgU2e4vm93E= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=MRwqshts; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="MRwqshts" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 85628C4CEE4; Mon, 5 May 2025 14:56:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1746456970; bh=bJ1ZR3VtEee2Lfg/kc3hGzfdhOtsDj5T36f80c1czIU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=MRwqshts24jqjgjY1AtD3qf06P0iH2vwFAk7rRhwRDq+kAF3AVGZOFjdShogWem1F Ia2HiFQAmi8PwvQ5/boqKCnj+ixY751rrAWJ4VWGkIJgh9o3IHj/DXXCvmDa2fm4UE HK7HsJrnuJf6WfgN+UfDAsl1AM8QSbmsLCxQWBrUSEdDluMUKWNRCtYFkjl29YOEvo KOHk4vMShT3Hg5qXjxz7bf6lETU3hz1YyE/kctreCQGzfpNCywnlx52ClHTealAnSy RGbkmcWx/e3j6o4lYfIbuvablzzwMC949ZlySeyIH2Qw5PwMSnlfg7muZNKzGYeW7Q eCdSjNUSxKhUA== Date: Mon, 5 May 2025 16:56:04 +0200 From: Christian Brauner To: =?utf-8?Q?Micka=C3=ABl_Sala=C3=BCn?= Cc: Eric Dumazet , Kuniyuki Iwashima , Oleg Nesterov , linux-fsdevel@vger.kernel.org, Jann Horn , "David S. Miller" , Alexander Viro , Daan De Meyer , David Rheinsberg , Jakub Kicinski , Jan Kara , Lennart Poettering , Luca Boccassi , Mike Yuan , Paolo Abeni , Simon Horman , Zbigniew =?utf-8?Q?J=C4=99drzejewski-Szmek?= , linux-kernel@vger.kernel.org, netdev@vger.kernel.org, Alexander Mikhalitsyn , linux-security-module@vger.kernel.org Subject: Re: [PATCH RFC v3 00/10] coredump: add coredump socket Message-ID: <20250505-unberechenbar-kosenamen-da3fb108080e@brauner> References: <20250505-work-coredump-socket-v3-0-e1832f0e1eae@kernel.org> <20250505.aFia3choo1aw@digikod.net> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20250505.aFia3choo1aw@digikod.net> On Mon, May 05, 2025 at 04:41:28PM +0200, Mickaël Salaün wrote: > On Mon, May 05, 2025 at 01:13:38PM +0200, 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: > > > > @linuxafsk/coredump_socket > > > > The "@" at the beginning indicates to the kernel that the abstract > > AF_UNIX coredump socket will be used to process coredumps. > > > > The coredump socket uses the fixed address "linuxafsk/coredump.socket" > > for now. > > > > The coredump socket is located in the initial network namespace. To bind > > the coredump socket userspace must hold CAP_SYS_ADMIN in the initial > > user namespace. Listening and reading can happen from whatever > > unprivileged context is necessary to safely process coredumps. > > > > When a task coredumps it opens a client socket in the initial network > > namespace and connects to the coredump socket. For now only tasks that > > are acctually coredumping are allowed to connect to the initial coredump > > socket. > > I think we should avoid using abstract UNIX sockets, especially for new Abstract unix sockets are at the core of a modern Linux system. During boot alone about 100 or so are created on a modern system when I counted during testing. Sorry, but this is a no-show argument.