CVE-2026-68147: fscrypt: Avoid dynamic allocation in fscrypt_get_devices()

From: Greg Kroah-Hartman <[email protected]>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

fscrypt: Avoid dynamic allocation in fscrypt_get_devices()

When a blk_crypto_key starts being used or is evicted, fs/crypto/ calls
fscrypt_get_devices() to get the filesystem's list of block devices,
then iterates over them and calls blk_crypto_config_supported(),
blk_crypto_start_using_key(), or blk_crypto_evict_key() on each one.

Currently, the block device pointers are placed in a dynamically
allocated array.  This dynamic allocation is problematic because:

- It can fail, especially at the fscrypt_destroy_inline_crypt_key() call
  site when it's invoked for inode eviction under direct reclaim.

- fscrypt_destroy_inline_crypt_key() doesn't handle the failure.  It
  just zeroizes and frees the blk_crypto_key without calling
  blk_crypto_evict_key().  That causes a use-after-free.

For now, let's fix this in the straightforward and easily-backportable
way by switching to an on-stack array.  Currently the fscrypt
multi-device functionality is used only by f2fs, which has a hardcoded
limit of 8 block devices.  An on-stack array works fine for that.

(Of course, this solution won't scale up to large number of block
devices.  For that we'd need a different solution, like moving the block
device iteration into the filesystem.  Or in the case of btrfs, which
will only support blk-crypto-fallback, we should make it just call
blk-crypto-fallback directly, so the block devices won't be needed.)

The Linux kernel CVE team has assigned CVE-2026-68147 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.1 with commit 22e9947a4b2ba255888541bd0111cf00b9b16586 and fixed in 6.6.148 with commit 4462ac3d90e897dda52ce4b6af2d526ddae835a8
	Issue introduced in 6.1 with commit 22e9947a4b2ba255888541bd0111cf00b9b16586 and fixed in 6.12.101 with commit 97a688563be71ec6fefc071aff69a66c69dbe244
	Issue introduced in 6.1 with commit 22e9947a4b2ba255888541bd0111cf00b9b16586 and fixed in 6.18.42 with commit 81ea8e8221853950c47dac7164f27c63a96f8f86
	Issue introduced in 6.1 with commit 22e9947a4b2ba255888541bd0111cf00b9b16586 and fixed in 7.1.6 with commit bc2d630296e0e049210ec05ff08459a6893ae749
	Issue introduced in 6.1 with commit 22e9947a4b2ba255888541bd0111cf00b9b16586 and fixed in 7.2-rc5 with commit 6fe4e4b8259e1330945b5f3c9476e08473b8e0e8

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-68147
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	fs/crypto/inline_crypt.c
	fs/f2fs/super.c
	include/linux/fscrypt.h


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/4462ac3d90e897dda52ce4b6af2d526ddae835a8
	https://git.kernel.org/stable/c/97a688563be71ec6fefc071aff69a66c69dbe244
	https://git.kernel.org/stable/c/81ea8e8221853950c47dac7164f27c63a96f8f86
	https://git.kernel.org/stable/c/bc2d630296e0e049210ec05ff08459a6893ae749
	https://git.kernel.org/stable/c/6fe4e4b8259e1330945b5f3c9476e08473b8e0e8