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 879B82C1AD for ; Wed, 28 Feb 2024 08:18:03 +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=1709108283; cv=none; b=fpOVsTubd8GhbQ2wkefq0DGbsKIhYRXDR48Hq5SO2IcGvfo7OzMnRzDaQkn6GS1laGW7cZHoM3x9vQ6czRqJKFVezigXWnrMDqAVUNZmx9Z/UEsqnVZmcD0z0N9dyk6680TOfY/IlGjTj8MiwkBW3KFch3ChatX4L2pGan9Kavk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1709108283; c=relaxed/simple; bh=omWmSPBBG3fhg35dtrwSvJO/MxmUqWmzBuEZMHQ0tIU=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=M/fG5GO7mlEGhq/mP0UiecB5jUc4ylw1McscFLv4A2/lwOMiesmKWCF+96+h2NaZmIHhFdUDtLOwVL2v7DvPVhaU3b4Ot77FXFVOv/LNcrCYeyO+j9UyBaP3dXzBU90wc05ftL/l07M45rtWCRI5cFxbdYIQ9uZ+GLv/oJk8dsY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=iLFQZrKG; 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="iLFQZrKG" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 17C95C433C7; Wed, 28 Feb 2024 08:18:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1709108283; bh=omWmSPBBG3fhg35dtrwSvJO/MxmUqWmzBuEZMHQ0tIU=; h=From:To:Cc:Subject:Date:Reply-to:From; b=iLFQZrKGV+4klzwH/6pBchOWBdnmqDjb7eq3HR9aAunh+iznZ7u35iqlpVlw5hrfE sFUvewngIgurYrPMEqeo//MWF1VG8UzDaZ8YHcqIJbHVOs0NVLk17NTln/BMbSOK+i Qogi/qk9kVDkTj/DfZr7NRgOvQWZtqQzetqZmT9s= From: Greg Kroah-Hartman To: linux-cve-announce@vger.kernel.org Cc: gregkh@kernel.org Subject: CVE-2021-47044: sched/fair: Fix shift-out-of-bounds in load_balance() Date: Wed, 28 Feb 2024 09:15:32 +0100 Message-ID: <2024022839-CVE-2021-47044-2e16@gregkh> X-Mailer: git-send-email 2.44.0 Precedence: bulk X-Mailing-List: linux-cve-announce@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Reply-to: , X-Developer-Signature: v=1; a=openpgp-sha256; l=3718; i=gregkh@linuxfoundation.org; h=from:subject:message-id; bh=SusXK9mVuPDS1aMPTIeaYmv9Nhed2wgfvIwEm8rGDyw=; b=owGbwMvMwCRo6H6F97bub03G02pJDKn3Xuf/q1qldCX9X8tnpo8x807cEH7Ub/nn6eK757uYj 0/YkfzgZ0csC4MgE4OsmCLLl208R/dXHFL0MrQ9DTOHlQlkCAMXpwBMpNCQYcFGlm833Pc8zDMv yc3W/LDd1/YMUy3DXLkd+44oGayeuD3WtkBxa9+hrNkfcgA= X-Developer-Key: i=gregkh@linuxfoundation.org; a=openpgp; fpr=F4B60CC5BF78C2214A313DCB3147D40DDB2DFB29 Content-Transfer-Encoding: 8bit From: gregkh@kernel.org Description =========== In the Linux kernel, the following vulnerability has been resolved: sched/fair: Fix shift-out-of-bounds in load_balance() Syzbot reported a handful of occurrences where an sd->nr_balance_failed can grow to much higher values than one would expect. A successful load_balance() resets it to 0; a failed one increments it. Once it gets to sd->cache_nice_tries + 3, this *should* trigger an active balance, which will either set it to sd->cache_nice_tries+1 or reset it to 0. However, in case the to-be-active-balanced task is not allowed to run on env->dst_cpu, then the increment is done without any further modification. This could then be repeated ad nauseam, and would explain the absurdly high values reported by syzbot (86, 149). VincentG noted there is value in letting sd->cache_nice_tries grow, so the shift itself should be fixed. That means preventing: """ If the value of the right operand is negative or is greater than or equal to the width of the promoted left operand, the behavior is undefined. """ Thus we need to cap the shift exponent to BITS_PER_TYPE(typeof(lefthand)) - 1. I had a look around for other similar cases via coccinelle: @expr@ position pos; expression E1; expression E2; @@ ( E1 >> E2@pos | E1 >> E2@pos ) @cst depends on expr@ position pos; expression expr.E1; constant cst; @@ ( E1 >> cst@pos | E1 << cst@pos ) @script:python depends on !cst@ pos << expr.pos; exp << expr.E2; @@ # Dirty hack to ignore constexpr if exp.upper() != exp: coccilib.report.print_report(pos[0], "Possible UB shift here") The only other match in kernel/sched is rq_clock_thermal() which employs sched_thermal_decay_shift, and that exponent is already capped to 10, so that one is fine. The Linux kernel CVE team has assigned CVE-2021-47044 to this issue. Affected and fixed versions =========================== Issue introduced in 5.10 with commit 5a7f55590467 and fixed in 5.10.37 with commit 80862cbf76c2 Issue introduced in 5.10 with commit 5a7f55590467 and fixed in 5.11.21 with commit 2f3eab368e31 Issue introduced in 5.10 with commit 5a7f55590467 and fixed in 5.12.4 with commit 805cea93e66c Issue introduced in 5.10 with commit 5a7f55590467 and fixed in 5.13 with commit 39a2a6eb5c9b Please see https://www.kernel.org or 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-2021-47044 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: kernel/sched/fair.c kernel/sched/sched.h 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/80862cbf76c2646f709a57c4517aefe0b094c774 https://git.kernel.org/stable/c/2f3eab368e313dba35fc2f51ede778bf7b030b54 https://git.kernel.org/stable/c/805cea93e66ca7deaaf6ad3b67224ce47c104c2f https://git.kernel.org/stable/c/39a2a6eb5c9b66ea7c8055026303b3aa681b49a5