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 NAKed by Eric W. Biederman as an ineffective mitigation: https://lore.kernel.org/all/[email protected]/ Wander Lairson Costa's RFC v2 received design feedback and no v3 ever followed: https://lore.kernel.org/all/[email protected]/ The flagged logic is unchanged today: fs/exec.c still selects TASK_DUMPABLE_OWNER in that case, and fs/coredump.c only rejects relative core paths when dumpable is 2, so the dumpable==1 case this CVE describes is not covered. Ubuntu records "no fix upstream as of 2022-01-27" and defers it for all releases; Debian lists src:linux as unfixed: https://ubuntu.com/security/CVE-2021-3864 https://security-tracker.debian.org/tracker/CVE-2021-3864 Red Hat rates RHEL 8 and later "Not affected" purely because their default core_pattern does not write relative to the current directory: https://access.redhat.com/security/cve/CVE-2021-3864 Images that set an absolute path, a pipe or a socket core_pattern (for example systemd-coredump) are not exploitable for the same reason. CC: Paul Barker <[email protected]> AI-Generated: Uses Claude (claude-opus-5) Signed-off-by: Junjie Cao <[email protected]> --- changes in v2: - split out of the single combined patch, one CVE per patch as requested - added primary source links (disclosures, distribution trackers, mailing list threads, upstream commits) to every commit message - added the three CVEs with no upstream fix as "unpatched" entries instead of leaving them undocumented - disclosed AI assistance per the contributor guide v1: https://lore.kernel.org/openembedded-core/[email protected]/ meta/recipes-kernel/linux/cve-exclusion.inc | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/meta/recipes-kernel/linux/cve-exclusion.inc b/meta/recipes-kernel/linux/cve-exclusion.inc index 9012d328..d7ae3b03 100644 --- a/meta/recipes-kernel/linux/cve-exclusion.inc +++ b/meta/recipes-kernel/linux/cve-exclusion.inc @@ -206,3 +206,9 @@ host model, no kernel fix exists or is planned, mitigated by firewall configurat # https://bugzilla.redhat.com/show_bug.cgi?id=1931327 CVE_STATUS[CVE-2021-3714] = "upstream-wontfix: inherent design limitation of \ KSM page deduplication, closed WONTFIX by Red Hat, no upstream fix planned" + +# Two fix attempts, neither merged; the fs/exec.c logic is unchanged. +# An absolute, piped or socket kernel.core_pattern prevents exploitation. +# https://www.openwall.com/lists/oss-security/2021/10/20/2 +CVE_STATUS[CVE-2021-3864] = "upstream-wontfix: no accepted mainline fix after \ +several attempts, exploitation requires a relative kernel.core_pattern" -- 2.43.0
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