From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3685E3F0755 for ; Fri, 8 May 2026 14:25:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778250308; cv=none; b=O7NZmVNmRYtccya0X8BMBOUKGNtcMSryECqSAMbG+bndNpeQpYU62+61E9Wzofk8UWLX9dRwyNBrGMV5syOe9nSv2vzkeFYWT+xQYCpfkESF2av810DQEWGyt3+aHuyE/7KWCvZSdmAGKeZuYZ3+PBKF5ACphk/vVKs03VP8SCc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778250308; c=relaxed/simple; bh=4hinr6czEabcxKjU06NuoQeF5oCMw0VtDFsWVodP638=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=uS8l7LxKeMc4O0ow1ZwGeOWHMEI6llzP071i/MUJBkAC0EhJ03CSLohjCb+RkCJ/yGPGwx9kvRnH1au87DffcEGia2fDrRQ8XET72b8PCzFbQNQd4NkdYdniLipKJgmcycboUwES6RA8tRXSDoj2/WzRazJkoWxapJsOmnXesPQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=dmVwzzC8; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="dmVwzzC8" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C121DC2BCB0; Fri, 8 May 2026 14:25:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1778250308; bh=4hinr6czEabcxKjU06NuoQeF5oCMw0VtDFsWVodP638=; h=From:To:Cc:Subject:Date:Reply-To:From; b=dmVwzzC8Yc32u76mLH4LthczoHDvIo4kAVaMRhNc3KXiwArnmtKj+h6NLLoUboW3k bvavBKT2tgTAghLE5joxa3d6Onl3YCLNWAXqHogb6zCw4HKwFhjqNFsvc/xo1E+pj1 1PAmwkZ7e/sig7gRjkVrx14N0hFIvUHygGVpYTZY= From: Greg Kroah-Hartman To: linux-cve-announce@vger.kernel.org Cc: Greg Kroah-Hartman Subject: CVE-2026-43418: sched/mmcid: Prevent CID stalls due to concurrent forks Date: Fri, 8 May 2026 16:22:27 +0200 Message-ID: <2026050846-CVE-2026-43418-8b7a@gregkh> X-Mailer: git-send-email 2.54.0 Reply-To: , Precedence: bulk X-Mailing-List: linux-cve-announce@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=2800; i=gregkh@linuxfoundation.org; h=from:subject:message-id; bh=85KiJEK6APozDoiYeT+0Hub+viRzx/vFL6SuREHAvqw=; b=owGbwMvMwCRo6H6F97bub03G02pJDJl/P1a5TZv6fIeQEcNetmBX1S8TBT7JNQTyPj+TYM6wJ yn23qkzHbEsDIJMDLJiiixftvEc3V9xSNHL0PY0zBxWJpAhDFycAjCRoyUMC+Z+vuB3zUflX+wO 799OVcY3K3Lr9Rnm2QjcuqF85b0qp+zsfR/EFYQab11dAQA= X-Developer-Key: i=gregkh@linuxfoundation.org; a=openpgp; fpr=F4B60CC5BF78C2214A313DCB3147D40DDB2DFB29 Content-Transfer-Encoding: 8bit From: Greg Kroah-Hartman Description =========== In the Linux kernel, the following vulnerability has been resolved: sched/mmcid: Prevent CID stalls due to concurrent forks A newly forked task is accounted as MMCID user before the task is visible in the process' thread list and the global task list. This creates the following problem: CPU1 CPU2 fork() sched_mm_cid_fork(tnew1) tnew1->mm.mm_cid_users++; tnew1->mm_cid.cid = getcid() -> preemption fork() sched_mm_cid_fork(tnew2) tnew2->mm.mm_cid_users++; // Reaches the per CPU threshold mm_cid_fixup_tasks_to_cpus() for_each_other(current, p) .... As tnew1 is not visible yet, this fails to fix up the already allocated CID of tnew1. As a consequence a subsequent schedule in might fail to acquire a (transitional) CID and the machine stalls. Move the invocation of sched_mm_cid_fork() after the new task becomes visible in the thread and the task list to prevent this. This also makes it symmetrical vs. exit() where the task is removed as CID user before the task is removed from the thread and task lists. The Linux kernel CVE team has assigned CVE-2026-43418 to this issue. Affected and fixed versions =========================== Issue introduced in 6.19 with commit fbd0e71dc370af73f6b316e4de9eed273dd90340 and fixed in 6.19.9 with commit f0189d49282e0458f3a737bd486c1ec048148f66 Issue introduced in 6.19 with commit fbd0e71dc370af73f6b316e4de9eed273dd90340 and fixed in 7.0 with commit b2e48c429ec54715d16fefa719dd2fbded2e65be 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-2026-43418 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: include/linux/sched.h kernel/fork.c kernel/sched/core.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/f0189d49282e0458f3a737bd486c1ec048148f66 https://git.kernel.org/stable/c/b2e48c429ec54715d16fefa719dd2fbded2e65be