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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6AABEC3ABC3 for ; Tue, 13 May 2025 23:16:00 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 88D9E6B00C1; Tue, 13 May 2025 19:15:58 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 80FD86B00C2; Tue, 13 May 2025 19:15:58 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6B1906B00D3; Tue, 13 May 2025 19:15:58 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 4754B6B00C1 for ; Tue, 13 May 2025 19:15:58 -0400 (EDT) Received: from smtpin07.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id D72BB16196F for ; Tue, 13 May 2025 23:15:58 +0000 (UTC) X-FDA: 83439444396.07.2EB9E51 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf26.hostedemail.com (Postfix) with ESMTP id 0CD42140003 for ; Tue, 13 May 2025 23:15:56 +0000 (UTC) Authentication-Results: imf26.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=lbyrfekk; spf=pass (imf26.hostedemail.com: domain of kees@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=kees@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1747178157; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=D1xptH/oUUu2Ir6TIND9ijE6bIO59tshllRcbOwV8RA=; b=lYXVyoalnwh6Xst2Ymk514HERMOf8Ovbm3QrqmEQE+LGxX7lxQX8JTMp8SI5fZ0a+jHZuQ xWpTA0v5h3jmJANxrgwQEeY9G4QtViWGcQdK/PcBbwrm6dC/kJmV0xl9sDFokXd9qInm/p WTuJ+qJVfPHwoKSJkrGXIAp4TKEkF20= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1747178157; a=rsa-sha256; cv=none; b=WuC+26uf8rkVFeArT1BpL2A6SxCiAurGzgAbLpC54Wqsc4kDtjBkYuSfVbb3Vm3ssZA2oe +NGIvd5RKuD5Lx+nKxB7orAZ5JFJ+SCsURNx6Tbs0zQ2wlVNGupv++9EKV3BGL2e8Gbi7P WWcvZbtCn8Sl8ZFWkMJ1jwo3j6Mg0kY= ARC-Authentication-Results: i=1; imf26.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=lbyrfekk; spf=pass (imf26.hostedemail.com: domain of kees@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=kees@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id B2B124ACED; Tue, 13 May 2025 23:15:55 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 71D25C4CEE4; Tue, 13 May 2025 23:15:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1747178155; bh=D1xptH/oUUu2Ir6TIND9ijE6bIO59tshllRcbOwV8RA=; h=Date:From:To:CC:Subject:In-Reply-To:References:From; b=lbyrfekkL4E0T/hAUnBfDulhbb6usyNaJtme2vR2/ky2gRqD+ndeR3IniYfurhtZh lLhSVaSXdO0Ww+iGUxipKvrtqkP1qyTQvKzeiN1r0ijh5byJ/5sgY4jzOj2ESU/2dP ciDrdAQS849TJBCLZ99kl5mI33j18FhF80nfH6RDA9N4gcxqbNTKmow6aZU66sZ+8L +ovjKTewFSR1ErUBCCCu8DtURdLrjSH41VA2veimgDUTEznRiHJiWIJ0hHVgfvlfJj BKEfccUhY9NS1gJGonGxMd2/oWo4JXjvpkUcbSMmQF22CR5tUZt88pDqX+zZRKjnJx AZ1mLZBpGBQ4w== Date: Tue, 13 May 2025 16:15:52 -0700 From: Kees Cook To: Jann Horn CC: Mateusz Guzik , Kees Cook , Christian Brauner , Eric Biederman , Jorge Merlino , Alexander Viro , Thomas Gleixner , Andy Lutomirski , Sebastian Andrzej Siewior , Andrew Morton , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, John Johansen , Paul Moore , James Morris , "Serge E. Hallyn" , Stephen Smalley , Eric Paris , Richard Haines , Casey Schaufler , Xin Long , "David S. Miller" , Todd Kjos , Ondrej Mosnacek , Prashanth Prahlad , Micah Morton , Fenghua Yu , Andrei Vagin , linux-kernel@vger.kernel.org, apparmor@lists.ubuntu.com, linux-security-module@vger.kernel.org, selinux@vger.kernel.org, linux-hardening@vger.kernel.org, oleg@redhat.com Subject: Re: [PATCH 1/2] fs/exec: Explicitly unshare fs_struct on exec User-Agent: K-9 Mail for Android In-Reply-To: References: <20221006082735.1321612-1-keescook@chromium.org> <20221006082735.1321612-2-keescook@chromium.org> <20221006090506.paqjf537cox7lqrq@wittgenstein> <86CE201B-5632-4BB7-BCF6-7CB2C2895409@chromium.org> Message-ID: <6C9B4DB6-0E73-471D-A278-39F61A825DB6@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 0CD42140003 X-Stat-Signature: gns7cqkabpwtesif75u8cewn6ih7w7ma X-Rspam-User: X-HE-Tag: 1747178156-930533 X-HE-Meta: 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 TI88xcfh Z/0JsQOpHk++nn0DjNKLpJWiI/97Add8JMzi8rP3Tf0vxHz0haTGRIKp9YGysFI/1+nBzveloI3wz8tjqr1NNla1vhgupm1VuE/bHTjJjwkWzXkih0oW6zSQYnv/ezCKDyToLfqWmplbTgn+lQbjK7euwcQjJ3Y5AxOtkrOpks+Qok1ict1LFKml5bXAuceifxKedsj9Tvgzfnt0002ihfa0sXapJwIJDuUbbjFvkq6RqcPlgifkApddQB6kZX80Joo9GtaWS03DIVJWz9PXoSRdORC3R140vypYbXwF3uEeyt8urdVwvafXWZTnkckpqmC1b8iGZi6UvW0Zjcqtgok2SNUhmPHL1x/KP+U2iyjLmyhLGfYI+rVMBDoKlQwa37Sh9mCaA7hh3LCms6wJZF/ptYa2CA29XAYPw X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On May 13, 2025 2:09:48 PM PDT, Jann Horn wrote: >On Tue, May 13, 2025 at 10:57=E2=80=AFPM Kees Cook wr= ote: >> On May 13, 2025 6:05:45 AM PDT, Mateusz Guzik wro= te: >> >Here is my proposal: *deny* exec of suid/sgid binaries if fs_struct is >> >shared=2E This will have to be checked for after the execing proc beco= mes >> >single-threaded ofc=2E >> >> Unfortunately the above Chrome helper is setuid and uses CLONE_FS=2E > >Chrome first launches a setuid helper, and then the setuid helper does >CLONE_FS=2E Mateusz's proposal would not impact this usecase=2E > >Mateusz is proposing to block the case where a process first does >CLONE_FS, and *then* one of the processes sharing the fs_struct does a >setuid execve()=2E Linux already downgrades such an execve() to be >non-setuid, which probably means anyone trying to do this will get >hard-to-understand problems=2E Mateusz' proposal would just turn this >hard-to-debug edgecase, which already doesn't really work, into a >clean error; I think that is a nice improvement even just from the >UAPI standpoint=2E > >If this change makes it possible to clean up the kernel code a bit, even = better=2E Ah! Okay, I appreciate the clarification=2E :) I'm game to try making it a= n error instead of silent downgrading=2E -Kees --=20 Kees Cook --=20 Kees Cook