[OE-core][PATCH v3 9/9] cve-exclusions: set status for CVE-2023-6240

[Junjie Cao <junjie.cao@linux.dev>]

"Marvin" is Hubert Kario's Bleichenbacher-style timing oracle research:

  https://people.redhat.com/~hkario/marvin/

The affected code is the generic software RSA PKCS#1 v1.5 unpadding in
crypto/rsa-pkcs1pad.c. pkcs1pad_decrypt_complete() has three
secret-dependent early exits (leading zero byte, block type, minimum
padding length) and a loop whose trip count depends on the position of
the separator, so the time taken reveals padding validity. There is no
constant-time unpadding or implicit-rejection fallback in the tree.

Red Hat classifies it CWE-203 and has shipped fixes only in RHEL errata
(RHSA-2024:2758, RHSA-2024:3618 and others); the bugzilla is still NEW.
Ubuntu records it unfixed upstream as of 2024-08-24 and Debian lists
src:linux vulnerable in all suites:

  https://access.redhat.com/security/cve/CVE-2023-6240
  https://ubuntu.com/security/CVE-2023-6240
  https://security-tracker.debian.org/tracker/CVE-2023-6240

Practical exposure is narrow: kernel PKCS#1 v1.5 use is dominated by
signature verification rather than decryption, and an attacker needs a
service driving KEYCTL_PKEY_DECRYPT with a long-lived key. The leaky
primitive is nevertheless reachable.

CC: Paul Barker <paul@pbarker.dev>
AI-Generated: Uses Claude (claude-opus-5)
Signed-off-by: Junjie Cao <junjie.cao@linux.dev>
---
v3:
- drop the Marvell/s390 aside and the unrelated e8829ef1f73f paragraph
  flagged in review as LLM confusion artifacts

v2: https://lore.kernel.org/openembedded-core/20260803084827.1348810-1-junjie.cao@linux.dev/

 meta/recipes-kernel/linux/cve-exclusion.inc | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/meta/recipes-kernel/linux/cve-exclusion.inc b/meta/recipes-kernel/linux/cve-exclusion.inc
index 35e0a66..637f8b6 100644
--- a/meta/recipes-kernel/linux/cve-exclusion.inc
+++ b/meta/recipes-kernel/linux/cve-exclusion.inc
@@ -252,3 +252,10 @@ affected fs/jfs txEnd()/lmLogClose() unmount race is unchanged"
 # https://lore.kernel.org/linux-nvme/20231016060519.231880-1-joshi.k@samsung.com/
 CVE_STATUS[CVE-2023-6238] = "unpatched: the proposed fix was applied to \
 nvme-6.6 and then reverted, no upstream fix has landed since"
+
+# "Marvin": the PKCS#1 v1.5 unpadding in crypto/rsa-pkcs1pad.c branches on
+# secret-derived data, leaking padding validity by timing. Still present in
+# mainline; fixed only in RHEL errata.
+# https://people.redhat.com/~hkario/marvin/
+CVE_STATUS[CVE-2023-6240] = "unpatched: Bleichenbacher-style timing oracle in \
+crypto/rsa-pkcs1pad.c is still present in mainline, fixed only downstream in RHEL"
-- 
2.43.0