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[174.109.172.136]) by smtp.gmail.com with ESMTPSA id v185sm7964175qki.26.2020.08.24.11.28.40 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 24 Aug 2020 11:28:41 -0700 (PDT) Subject: Re: [PATCH v5 2/9] fs: add O_ALLOW_ENCODED open flag To: Omar Sandoval , linux-fsdevel@vger.kernel.org, linux-btrfs@vger.kernel.org, Al Viro , Christoph Hellwig Cc: Dave Chinner , Jann Horn , Amir Goldstein , Aleksa Sarai , linux-api@vger.kernel.org, kernel-team@fb.com References: From: Josef Bacik Message-ID: <3c44cdf2-e0fd-cea1-4028-d6315ba3b7fd@toxicpanda.com> Date: Mon, 24 Aug 2020 14:28:39 -0400 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-api-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On 8/21/20 3:38 AM, Omar Sandoval wrote: > From: Omar Sandoval > > The upcoming RWF_ENCODED operation introduces some security concerns: > > 1. Compressed writes will pass arbitrary data to decompression > algorithms in the kernel. > 2. Compressed reads can leak truncated/hole punched data. > > Therefore, we need to require privilege for RWF_ENCODED. It's not > possible to do the permissions checks at the time of the read or write > because, e.g., io_uring submits IO from a worker thread. So, add an open > flag which requires CAP_SYS_ADMIN. It can also be set and cleared with > fcntl(). The flag is not cleared in any way on fork or exec; it should > probably be used with O_CLOEXEC in most cases. > > Note that the usual issue that unknown open flags are ignored doesn't > really matter for O_ALLOW_ENCODED; if the kernel doesn't support > O_ALLOW_ENCODED, then it doesn't support RWF_ENCODED, either. It seemed like you agreed to require O_CLOEXEC to be set when using O_ALLOW_ENCODED in your last go around, what happened to that? I know I'd feel better if we had that requirement, and if we aren't I'd like to know why we can't. Thanks, Josef