+ mm-swap-reject-swapon-on-filesystem-level-encrypted-files.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/swap: reject swapon() on filesystem-level encrypted files
has been added to the -mm mm-new branch.  Its filename is
     mm-swap-reject-swapon-on-filesystem-level-encrypted-files.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-swap-reject-swapon-on-filesystem-level-encrypted-files.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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------------------------------------------------------
From: Eric Biggers <ebiggers@kernel.org>
Subject: mm/swap: reject swapon() on filesystem-level encrypted files
Date: Thu, 30 Jul 2026 11:48:53 -0700

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.

Link: https://lore.kernel.org/20260730184853.48347-1-ebiggers@kernel.org
Fixes: 9bd8212f981e ("ext4 crypto: add encryption policy and password salt support")
Fixes: f424f664f0e8 ("f2fs crypto: add encryption policy and password salt support")
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: Barry Song <baohua@kernel.org>
Cc: Chris Li <chrisl@kernel.org>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: "Darrick J. Wong" <djwong@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 Documentation/filesystems/fscrypt.rst |    4 ++++
 mm/swapfile.c                         |    4 ++++
 2 files changed, 8 insertions(+)

--- a/Documentation/filesystems/fscrypt.rst~mm-swap-reject-swapon-on-filesystem-level-encrypted-files
+++ a/Documentation/filesystems/fscrypt.rst
@@ -1238,6 +1238,10 @@ astute users may notice some differences
 
 - 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
--- a/mm/swapfile.c~mm-swap-reject-swapon-on-filesystem-level-encrypted-files
+++ a/mm/swapfile.c
@@ -3662,6 +3662,10 @@ SYSCALL_DEFINE2(swapon, const char __use
 		error = -EBUSY;
 		goto bad_swap_unlock_inode;
 	}
+	if (IS_ENCRYPTED(inode)) {
+		error = -EINVAL;
+		goto bad_swap_unlock_inode;
+	}
 
 	/*
 	 * The swap subsystem needs a major overhaul to support this.
_

Patches currently in -mm which might be from ebiggers@kernel.org are

mm-swap-reject-swapon-on-filesystem-level-encrypted-files.patch