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 96ACF1B86DB; Wed, 7 Aug 2024 11:37:23 +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=1723030643; cv=none; b=TlYiBAV2kCHnVgwZJvs6ZDVtlTDSiPIP2KHVIa2kGPtLjVaDlLewuK4FJF/2Q0ITxXJT+G5zfG93B8zzoXs9gKXwwwxrxwdqNh+YaYqBuTwdV8d5zTpc8D44jJLaJP8rzNrWpw37wYQ0D9ZbDKFtMycQY6ZNRTfjB5wz0CyRoIo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723030643; c=relaxed/simple; bh=f36Eut4cpuTeN/nHR83eH313AyJ5JQ3s2RGRYRnZE2U=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=F9zV/s5GB/DvK8J96EayTFDpPqrMAzMm4HJa0/dnCCpoZJCwtpaWwDh8pUf9qvekAqsxpQaFFPSJwDVDqUtH5UoEBYjyuW3H9tslJ1MpvTnZ+XlEhPCS/7Zn6Za60u+J9QUtHZAU6RlwBev8Wr6V1CwdyA7GgUuvxdrS3CuwkBU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=U5BQyklx; 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="U5BQyklx" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2FBAAC32782; Wed, 7 Aug 2024 11:37:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1723030643; bh=f36Eut4cpuTeN/nHR83eH313AyJ5JQ3s2RGRYRnZE2U=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=U5BQyklxnmNN5PAXzuPelTAWieKNWfAsDmMIfL6P1mZ1nq+oy7hBxwu7BgG6CW0Cf MANwNVDDKlb+/RtVlrjpxcyVAWb8UCkDS17WsJwjB2JFDb7gsmFpSu5zEeABoAk+uh LY5lkJfGKMIYcBixGENYZT9XAqoNlArnLzpOEv4xfF5s0RE9Z1o87t/AqT/J8OKPbr 7faYb3lVH4mef0qPvRQvjDjru+nbiAYdM2UuGR+qerm1kgcB1U9eTx0HDDto0dcu7/ 9Tgx5fzaAc+nRxG23Tn9Bf8QSWiFCRvRNda7pD9chEFE22oPcTk+lsTOwHs73W9auG ybhnGmm9Y2Lxw== Message-ID: <0892524d-e9c1-4b27-8622-11cd697451ea@kernel.org> Date: Wed, 7 Aug 2024 19:37:22 +0800 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] f2fs: Require FMODE_WRITE for atomic write ioctls To: Jann Horn , Jaegeuk Kim Cc: linux-f2fs-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20240806-f2fs-atomic-write-v1-1-8a586e194fd7@google.com> Content-Language: en-US From: Chao Yu Autocrypt: addr=chao@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2024/8/6 22:07, Jann Horn wrote: > The F2FS ioctls for starting and committing atomic writes check for > inode_owner_or_capable(), but this does not give LSMs like SELinux or > Landlock an opportunity to deny the write access - if the caller's FSUID > matches the inode's UID, inode_owner_or_capable() immediately returns true. > > There are scenarios where LSMs want to deny a process the ability to write > particular files, even files that the FSUID of the process owns; but this > can currently partially be bypassed using atomic write ioctls in two ways: > > - F2FS_IOC_START_ATOMIC_REPLACE + F2FS_IOC_COMMIT_ATOMIC_WRITE can > truncate an inode to size 0 > - F2FS_IOC_START_ATOMIC_WRITE + F2FS_IOC_ABORT_ATOMIC_WRITE can revert > changes another process concurrently made to a file > > Fix it by requiring FMODE_WRITE for these operations, just like for > F2FS_IOC_MOVE_RANGE. Since any legitimate caller should only be using these > ioctls when intending to write into the file, that seems unlikely to break > anything. > > Fixes: 88b88a667971 ("f2fs: support atomic writes") > Cc: stable@vger.kernel.org > Signed-off-by: Jann Horn Reviewed-by: Chao Yu Thanks,