CVE-2026-74590: fsverity: Fix bpf_get_fsverity_digest() dynptr assumptions

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

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

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

fsverity: Fix bpf_get_fsverity_digest() dynptr assumptions

The BPF verifier and the dynptr abstraction ensure that the memory space
referenced by a dynptr remains valid.  They do not, however, provide any
guarantee that the contents of the memory are stable.  kfuncs are
expected to remain memory-safe even if concurrent modifications occur.

bpf_get_fsverity_digest() didn't follow that: it could crash if
arg->digest_size was concurrently modified.

Fix that by using the known-good value hash_alg->digest_size instead.

Also widen 'dynptr_sz' and 'out_digest_sz' to u64 to match the return
type of __bpf_dynptr_size().  It doesn't appear that it can actually be
more than INT_MAX currently (since __bpf_dynptr_data_rw() excludes
file-based pointers), but the correct type might as well be used.

The Linux kernel CVE team has assigned CVE-2026-74590 to this issue.


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

	Issue introduced in 6.8 with commit 67814c00de3161181cddd06c77aeaf86ac4cc584 and fixed in 6.12.104 with commit 1344b632cb5043e32939a84568125719111c5af3
	Issue introduced in 6.8 with commit 67814c00de3161181cddd06c77aeaf86ac4cc584 and fixed in 6.18.45 with commit 2a5cfcad1d56e26d645b7887b0ed24c371851525
	Issue introduced in 6.8 with commit 67814c00de3161181cddd06c77aeaf86ac4cc584 and fixed in 7.1.9 with commit 5bd63cad9df4328a184c409fbdad4f17944bcdb8
	Issue introduced in 6.8 with commit 67814c00de3161181cddd06c77aeaf86ac4cc584 and fixed in 7.2 with commit 3e8ec7c0387273329374f5c7bd61f5f38af71fe1

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-2026-74590
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/verity/measure.c


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/1344b632cb5043e32939a84568125719111c5af3
	https://git.kernel.org/stable/c/2a5cfcad1d56e26d645b7887b0ed24c371851525
	https://git.kernel.org/stable/c/5bd63cad9df4328a184c409fbdad4f17944bcdb8
	https://git.kernel.org/stable/c/3e8ec7c0387273329374f5c7bd61f5f38af71fe1