From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-180.mta1.migadu.com (out-180.mta1.migadu.com [95.215.58.180]) (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 189D22E6116; Fri, 31 Jul 2026 15:11:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.180 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785510689; cv=none; b=aQr6SKGRj28DrBdub4ayjxlq+s4/0zqjTXGk/UeGRFLO5Vzql0FUHtRdeJPb6kK4ZbNjJVx2oZMBpRBaP3O+bICSvSQoVmLA3TsYG10PVvBo2h4REgoCVmPFFg4ccqO3lGUMDOScE0lhXFVn2gd12sOfKK+644hwb4yzheRJbzg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785510689; c=relaxed/simple; bh=ifviHQm94ylXfpXEdFpn4qmwWPwyoSq7qx/7zBSGoiI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Y4Nv3mDX/1bg+ht054UE7rSI2k1k95Sthr8QXUEOwI/JGW+zOO2WPPlSnSli5wl2nevYRgEwn3pyV1OStKSAm1lUXhSSNe3FvMX/O/bnC+fG6VAwZ5bSHYUzoB34LJqtxP82t6it8TbqOSW2d/TQfM2/Zx8JsTbHW3yF9o9BkTc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=jD5wOdrf; arc=none smtp.client-ip=95.215.58.180 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="jD5wOdrf" Date: Fri, 31 Jul 2026 23:11:02 +0800 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1785510674; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=qo1LR7qrIwKJFtiU17ykHkbB13kJdtxhqwfYwUfZhvA=; b=jD5wOdrf8h5mlWbkWIIredTfjWIAiJ71znqBSjQ7zbpML8PWy6RmmcRGZa7BCDL9qZfsqO uttlq0r3C6Ao7WiRTJedjWVOP1f4x8cSC63BJ6wDixAojIUP2Bczt0P/nV4vsRWngQ7EiD bDcZFs4H/FkW1LFUeXED4/+7zqbkY44= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Baoquan He To: Eric Biggers Cc: linux-mm@kvack.org, Andrew Morton , 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 , Barry Song , Youngjun Park , stable@vger.kernel.org Subject: Re: [PATCH] mm/swap: reject swapon() on filesystem-level encrypted files Message-ID: References: <20260730184853.48347-1-ebiggers@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260730184853.48347-1-ebiggers@kernel.org> X-Migadu-Flow: FLOW_OUT On 07/30/26 at 11:48am, 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") > Cc: stable@vger.kernel.org > Signed-off-by: Eric Biggers > --- > Documentation/filesystems/fscrypt.rst | 4 ++++ > mm/swapfile.c | 4 ++++ > 2 files changed, 8 insertions(+) > > diff --git a/Documentation/filesystems/fscrypt.rst b/Documentation/filesystems/fscrypt.rst > index c0dd35f1af12..cba1989777da 100644 > --- a/Documentation/filesystems/fscrypt.rst > +++ b/Documentation/filesystems/fscrypt.rst > @@ -1238,6 +1238,10 @@ astute users may notice some differences in behavior: > > - DAX (Direct Access) is not supported on encrypted files. > > +- Encrypted files cannot be used directly as swap files. To swap to > + an encrypted file, set up a loopback device on top of it. > + Alternatively, encrypted swap can use a dm-crypt device instead. > + > - The maximum length of an encrypted symlink is 2 bytes shorter than > the maximum length of an unencrypted symlink. For example, on an > EXT4 filesystem with a 4K block size, unencrypted symlinks can be up > diff --git a/mm/swapfile.c b/mm/swapfile.c > index 78b49b0658ad..e4991da81b5f 100644 > --- a/mm/swapfile.c > +++ b/mm/swapfile.c > @@ -3650,6 +3650,10 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) > error = -EBUSY; > goto bad_swap_unlock_inode; > } > + if (IS_ENCRYPTED(inode)) { > + error = -EINVAL; > + goto bad_swap_unlock_inode; > + } Sounds reasonable to me. One minor suggestion: it might be helpful to emit a pr_warn_once() explaining *why* the swapon was rejected and pointing users to the dm-crypt / loopback alternatives, so the -EINVAL isn't opaque. Optional though -- the check itself is what matters. And this patch updates fscrypt.rst. Would it be good to also update the swapon(8) man page to document the new -EINVAL condition? Other than these, Reviewed-by: Baoquan He > > /* > * The swap subsystem needs a major overhaul to support this. > > base-commit: f5098b6bae761e346ebcd9da7f95622c04733cff > -- > 2.55.0 >