[OE-core][PATCH v3 3/9] 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 an ineffective mitigation by Eric W. Biederman and the discussion
went quiet in 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/

The flagged logic is unchanged: fs/exec.c still selects
TASK_DUMPABLE_OWNER in that case, and fs/coredump.c only applies the
suid-safe restriction when dumpable is TASK_DUMPABLE_ROOT, so the
dumpable==1 case this CVE describes is not covered. Images that set an
absolute path, a pipe or a socket core_pattern are not exploitable.

CC: Paul Barker <paul@pbarker.dev>
AI-Generated: Uses Claude (claude-opus-5)
Signed-off-by: Junjie Cao <junjie.cao@linux.dev>
---
v3:
- use "unpatched" instead of "upstream-wontfix"; a NAK of one
  mitigation is not an upstream wontfix of the issue
- drop the "NAKed" wording: the discussion went quiet, it was not
  formally rejected

v2: https://lore.kernel.org/openembedded-core/20260803084827.1348810-1-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 af3576d..ba8e467 100644
--- a/meta/recipes-kernel/linux/cve-exclusion.inc
+++ b/meta/recipes-kernel/linux/cve-exclusion.inc
@@ -206,3 +206,11 @@ host model, no upstream kernel fix, mitigated by firewall configuration"
 # https://security-tracker.debian.org/tracker/CVE-2021-3714
 CVE_STATUS[CVE-2021-3714] = "unpatched: timing side channel inherent to \
 KSM page deduplication, only reachable when KSM is enabled and opted into"
+
+# Two mitigation attempts, neither merged; the fs/exec.c logic is
+# unchanged. An absolute, piped or socket kernel.core_pattern (for
+# example systemd-coredump) prevents exploitation.
+# https://www.openwall.com/lists/oss-security/2021/10/20/2
+# https://ubuntu.com/security/CVE-2021-3864
+CVE_STATUS[CVE-2021-3864] = "unpatched: no accepted mainline fix, \
+exploitation requires a relative kernel.core_pattern"
-- 
2.43.0