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b=iJnEVe1voUvv8oU3L/LXlxlWg/TMzmxWX/p+WsY0i3YPuE5mFSEJ4cF0TMcimIXHY ghjBzhczgWPekjA8dP0c5k00yvs2tMguPZfnVAQ1KarieF9XzeUMVueazl7OX9zaeG yRbcWd3iB0SupGRkN7oe2OwtgLEhQG1wvVdm67wE= Date: Thu, 30 Jul 2026 12:53:27 -0700 From: Andrew Morton To: Eric Biggers Cc: linux-mm@kvack.org, Chris Li , Kairui Song , linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-fscrypt@vger.kernel.org, linux-kernel@vger.kernel.org, Kemeng Shi , Nhat Pham , Baoquan He , Barry Song , Youngjun Park , stable@vger.kernel.org Subject: Re: [PATCH] mm/swap: reject swapon() on filesystem-level encrypted files Message-Id: <20260730125327.11fc9227d04f659a59136cdd@linux-foundation.org> In-Reply-To: <20260730184853.48347-1-ebiggers@kernel.org> References: <20260730184853.48347-1-ebiggers@kernel.org> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: DBFC8180008 X-Stat-Signature: rqhdua598967d4rf3cem1ib9o3q4feq6 X-HE-Tag: 1785441209-888767 X-HE-Meta: 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 H5Tbu7Iz DtNijQw/+xPn8ZscX6OdiQ8dD21vRNotxbL7spAGGPruxYAvJKDPdxpTnTA1hvbJHbO018Kr2RneyY7LYj3pADr/RkFN0ZNMyh7g3LGx90GtGo0pk4WSwMYoLQ6QC8XQAVVJlKjZx30mq8dgs25RjLRJ4I3/Id2G8vrZBdWKwAOyOv2bsj9sYvdDM5EPv9gbsSVt4LYxkLzUjY2mu9nlsMm6F7jg0J+r7WBtwCdPNNVgZuXTuHIeAmCgB4b9yiWcG5ZEgGTFLEtMr0UbkYYebmvlUTw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, 30 Jul 2026 11:48:53 -0700 Eric Biggers wrote: > ext4 and f2fs don't prevent filesystem-level encrypted files from being > set up directly as swap files. In this case, encryption is bypassed. > > No one should be doing this, vs. the methods of encrypted swap that > actually do work (such as swapping to a dm-crypt device, or swapping to > a loopback device on top of a filesystem-level encrypted file). > > Nevertheless, to prevent user error, make swapon() explicitly reject > this case. Document this behavior in fscrypt.rst as well. > > Fixes: 9bd8212f981e ("ext4 crypto: add encryption policy and password salt support") > Fixes: f424f664f0e8 ("f2fs crypto: add encryption policy and password salt support") Ouch. We are going to break ten year old setups? I don't think we can do this! I think the best we can do is to emit loud warnings which point the operator to some Documentation/ which tells operator that this deprecated configuration will be disallowed in, umm, 2029. > + Alternatively, encrypted swap can use a dm-crypt device instead. That's tautological. s/ intead// ;)