From bf4068dd83e0094ef1e9b2b370ecfdcd5ba9e6ba Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Mon, 3 Aug 2026 11:04:26 -0700 Subject: [PATCH] mm/swap: reject swapon() on filesystem-level encrypted files commit c310a8932a3107c9bc8f01d473e9d085f8aa9c98 upstream. 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/20260803180426.3123-1-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 Reviewed-by: Baoquan He Reviewed-by: Muhammad Usama Anjum Reviewed-by: "Darrick J. Wong" Cc: Barry Song Cc: Chris Li Cc: Kairui Song Cc: Kemeng Shi Cc: Nhat Pham Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- Documentation/filesystems/fscrypt.rst | 4 ++++ mm/swapfile.c | 7 +++++++ 2 files changed, 11 insertions(+) diff --git a/Documentation/filesystems/fscrypt.rst b/Documentation/filesystems/fscrypt.rst index 7940a45d3952..d39abc884352 100644 --- a/Documentation/filesystems/fscrypt.rst +++ b/Documentation/filesystems/fscrypt.rst @@ -1063,6 +1063,10 @@ 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. + - 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 c9b9053c7969..04f10e9c36c5 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -3209,6 +3209,13 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) error = -EBUSY; goto bad_swap_unlock_inode; } + if (IS_ENCRYPTED(inode)) { + pr_warn_once( + "Filesystem-level encrypted swapfile '%s' is unsupported. Create a loop device over it, or use dm-crypt\n", + name->name); + error = -EINVAL; + goto bad_swap_unlock_inode; + } /* * Read the swap header.