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 4AB11253B43; Tue, 11 Feb 2025 18:56:44 +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=1739300205; cv=none; b=FDJZDjWuU5Yrej0B624mnnQEH1g3/GvGxdsOWgNASSxKzHMMY2PBY8bYNV1XKqUe0qaLEDMpQduov0BEQ3TNyOVSEf9zRkeBSHUMehXPE5SEh4lgNv4/3Dfe0HN7nVJXu+TWcEb222VTMVVuaaKNPuNQsycryZiQ0umSdqiTq+8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739300205; c=relaxed/simple; bh=OZZ31STvBMH1Xz8EufSOw05ugO2ZmuZCuqyJ1O75NFM=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=ABW+zCU31g8+MW3Sh6UEYyjrA3uACeXA8zWqdh418UoMiK1ecDQq7xT50U6O+VveAiFqY4HFFkcpekwkGvBTJoMvwo+bobSIUCImqcgAfoabIlaic74VWOBejnNFxFhJbVCQBqZ3B5JDjo0+3pAoz8qa+KtGINiFFOMFO/vtveg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=pH/BTvMs; 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="pH/BTvMs" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EEA62C4CEDD; Tue, 11 Feb 2025 18:56:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1739300204; bh=OZZ31STvBMH1Xz8EufSOw05ugO2ZmuZCuqyJ1O75NFM=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=pH/BTvMs2RKtzr/DhmT9xZke47pG3hBN9jGhZi2eY8cTQVWtgsf56j1jC/LN42d6G JabRB+7J4EDqReLCRE7qZiMpDG5aZJ1LJURWrRqhhBj5ixiQ5nPRsk4lMoOfvvd37c AEz4zQcQRZKGrF7NG/c5k/Y6XV10wRNwnam+OfAQtOfyRfq4rRv4PCqnDl3USJ0Laj XGS+kUf30RE6W85XTWRbmMln6sTovWdTN4MSP/9HDQTtUZl3rIO3Orzpd+plBgYgvT jVJmtCxQSqUzKIsktx1lmkQmJ12++c1ld9HisG/9AsdIs70yCEtb7wtjDwliy+o5Hf TkzaQ+kvjLD+Q== Message-ID: Subject: Re: [PATCH 0/2] acct: don't allow access to internal filesystems From: Jeff Layton To: Christian Brauner , Zicheng Qu , Linus Torvalds Cc: axboe@kernel.dk, joel.granados@kernel.org, tglx@linutronix.de, viro@zeniv.linux.org.uk, hch@lst.de, len.brown@intel.com, pavel@ucw.cz, pengfei.xu@intel.com, rafael@kernel.org, tanghui20@huawei.com, zhangqiao22@huawei.com, judy.chenhui@huawei.com, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, syzkaller-bugs@googlegroups.com, linux-pm@vger.kernel.org, stable@vger.kernel.org Date: Tue, 11 Feb 2025 13:56:41 -0500 In-Reply-To: <20250211-work-acct-v1-0-1c16aecab8b3@kernel.org> References: <20250210-unordnung-petersilie-90e37411db18@brauner> <20250211-work-acct-v1-0-1c16aecab8b3@kernel.org> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; 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text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.54.3 (3.54.3-1.fc41) Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Tue, 2025-02-11 at 18:15 +0100, Christian Brauner wrote: > In [1] it was reported that the acct(2) system call can be used to > trigger a NULL deref in cases where it is set to write to a file that > triggers an internal lookup. >=20 > This can e.g., happen when pointing acct(2) to /sys/power/resume. At the > point the where the write to this file happens the calling task has > already exited and called exit_fs() but an internal lookup might be > triggered through lookup_bdev(). This may trigger a NULL-deref > when accessing current->fs. >=20 > This series does two things: >=20 > - Reorganize the code so that the the final write happens from the > workqueue but with the caller's credentials. This preserves the > (strange) permission model and has almost no regression risk. >=20 > - Block access to kernel internal filesystems as well as procfs and > sysfs in the first place. >=20 > This api should stop to exist imho. >=20 I wonder who uses it these days, and what would we suggest they replace it with? Maybe syscall auditing? config BSD_PROCESS_ACCT bool "BSD Process Accounting" depends on MULTIUSER help If you say Y here, a user level program will be able to instruct = the kernel (via a special system call) to write process accounting information to a file: whenever a process exits, information abou= t that process will be appended to the file by the kernel. The information includes things such as creation time, owning user, command name, memory usage, controlling terminal etc. (the comple= te list is in the struct acct in ). It i= s up to the user level program to do useful things with this information. This is generally a good idea, so say Y. Maybe at least time to replace that last sentence and make this default to 'n'? > Link: https://lore.kernel.org/r/20250127091811.3183623-1-quzicheng@huawei= .com [1] >=20 > Signed-off-by: Christian Brauner > --- > Christian Brauner (2): > acct: perform last write from workqueue > acct: block access to kernel internal filesystems >=20 > kernel/acct.c | 134 ++++++++++++++++++++++++++++++++++++----------------= ------ > 1 file changed, 84 insertions(+), 50 deletions(-) > --- > base-commit: af69e27b3c8240f7889b6c457d71084458984d8e > change-id: 20250211-work-acct-a6d8e92a5fe0 >=20 --=20 Jeff Layton