[OE-core][PATCH v4 3/8] cve-exclusions: set status for CVE-2021-3864

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

begin_new_exec() resets dumpability to owner-dumpable whenever the real
and effective ids match at exec time. A binary exec'd by a setuid
program that has already called setuid(0) therefore becomes dumpable as
root, and with a relative core_pattern plus an attacker-controlled
working directory the resulting core file can be dropped into a
privileged directory such as /etc/logrotate.d.

Full report with proof of concept:

  https://www.openwall.com/lists/oss-security/2021/10/20/2

Two fixes were proposed and neither was merged. Waiman Long's patch
was judged "not a particularly effective mitigation" by Eric W.
Biederman and the discussion went quiet by early 2022; Wander Lairson
Costa's RFC v2 received design feedback and no v3 followed:

  https://lore.kernel.org/all/20211221021744.864115-1-longman@redhat.com/
  https://lore.kernel.org/all/20211228170910.623156-1-wander@redhat.com/

CC: Paul Barker <paul@pbarker.dev>
AI-Generated: Uses Claude (claude-opus-5)
Signed-off-by: Junjie Cao <junjie.cao@linux.dev>
---
v4:
- use the review's comment and status wording; drop the coredump path
  analysis paragraph
- quote Biederman's assessment verbatim

v3: https://lore.kernel.org/openembedded-core/20260812072842.1176341-1-junjie.cao@linux.dev/

 meta/recipes-kernel/linux/cve-exclusion.inc | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/meta/recipes-kernel/linux/cve-exclusion.inc b/meta/recipes-kernel/linux/cve-exclusion.inc
index 36643ccc..36920e2c 100644
--- a/meta/recipes-kernel/linux/cve-exclusion.inc
+++ b/meta/recipes-kernel/linux/cve-exclusion.inc
@@ -206,3 +206,11 @@ model, no upstream fix"
 # https://ubuntu.com/security/CVE-2021-3714
 CVE_STATUS[CVE-2021-3714] = "unpatched: Timing side channel inherent to Kernel \
 Same-page Merging (KSM) page deduplication"
+
+# Triaged August 2026 - Two fixes proposed upstream but neither was merged,
+# attempts to fix seem to have petered out. Unfixed in Debian/Ubuntu.
+# https://lore.kernel.org/all/20211221021744.864115-1-longman@redhat.com/
+# https://lore.kernel.org/all/20211228170910.623156-1-wander@redhat.com/
+# https://security-tracker.debian.org/tracker/CVE-2021-3864
+# https://ubuntu.com/security/CVE-2021-3864
+CVE_STATUS[CVE-2021-3864] = "unpatched: Proposed fixes were not merged upstream"
-- 
2.43.0