Hi all, I discovered that it's possible for userspace to write to active swap files and swap devices. While activated, the kernel effectively holds an irrevocable (except by swapoff) longterm lease on the storage associated with the swap device, so we need to shut down this vector for memory corruption of userspace programs.
Nothing new for v3 other than rebasing against 5.3-rc4. If you're going to start using this mess, you probably ought to just pull from my git trees, which are linked below. This has been lightly tested with fstests. Enjoy! Comments and questions are, as always, welcome. --D kernel git tree: https://git.kernel.org/cgit/linux/kernel/git/djwong/xfs-linux.git/log/?h=immutable-swapfiles fstests git tree: https://git.kernel.org/cgit/linux/kernel/git/djwong/xfstests-dev.git/log/?h=immutable-swapfiles