From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 E84F5592204 for ; Thu, 17 Sep 2026 16:13:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789661603; cv=none; b=V9E4aju/QPaZc0cTWoYJQduGDEAoRxhVrmw/m7r2pykab0l2hhHqPlNvZ5fpwWkKBFBPlTLb33gOhpkagH208INHPXW96lNd/FEmAU4YFZ1+ZT548Eslwb/4uTZTJdNGO5rXKS58ib8jAtIoilqlehVpdM1Us8D2x3hlgJATT4w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789661603; c=relaxed/simple; bh=aoGeqpqy7iy2EDCTvbqNOuxihlc+hudKh1rK1dlhHCo=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=Wd2QsNwxLNFnRQR0PDK9MgNZCVO01d8H6ueN/TREclSE3FjfUoW60FpNHJ05m5jPhwAuCI3rDjqktCZZ23c/WyVoRRTJNEp69WWrnXHVV4Qy7yTvI/laV7TcnenTIZHrqE7PyC5nPq9SD947IOWo4MQx/iSa+8BW7xWJkm3idNM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=puAPNmD1; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="puAPNmD1" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1E1581F000FF; Thu, 17 Sep 2026 16:13:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1789661600; bh=HmMyfLakRG75ai+fmvoDVIRT+1RQRGkxoHINurPnkuo=; h=From:To:Cc:Subject:Date:Reply-To; b=puAPNmD1jlQrRukeq3W/RxHJ5r0dw5S7zlLPeiASJ9Q1GjRZV7Rg6ILSK5cEs5GmP Sc+u9TdyFTqAVcWKMx4WU3nX5HXzjCrwJdNZcYCYd8UPq/17axi4i4DDubQCi0TFlx tbCpZ6+rYduwprGnrPpDlvp+RZm1Y+g7MEo2y5FA= From: Greg Kroah-Hartman To: linux-cve-announce@vger.kernel.org Cc: Greg Kroah-Hartman Subject: CVE-2026-90075: net/sched: fq_codel: clamp default quantum and mtu Date: Thu, 17 Sep 2026 17:08:25 +0100 Message-ID: <2026091708-CVE-2026-90075-40b2@gregkh> X-Mailer: git-send-email 2.55.0 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=4216; i=gregkh@linuxfoundation.org; h=from:subject:message-id; bh=TGDPDHB2pUoCrm/yWm/BKT5D75UUgpmknWbeMlQotsw=; b=owGbwMvMwCRo6H6F97bub03G02pJDFlrBDLW2W2eWBJ5hqOsRundtHUlh79s9zoW/C7rbXHt0 gCj7zlKHbEsDIJMDLJiiixftvEc3V9xSNHL0PY0zBxWJpAhDFycAjARk6cMC05fFVHOTa4Q82q6 YKo1s/Ej0+bXPAzzXd5erS9bu85oKu+cKdXGr2Y5vNXXBQA= 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: net/sched: fq_codel: clamp default quantum and mtu fq_codel_init() sets q->quantum = psched_mtu(qdisc_dev(sch)) without clamping. A device with a huge MTU (e.g. dummy with max_mtu == 0 accepting MTU 2147483634) makes psched_mtu() return 0x80000000, which overflows the signed flow->deficit to INT_MIN in fq_codel_dequeue(), causing an infinite loop and soft lockup. Emulate fq_codel_change() and constrain to [256, FQ_CODEL_QUANTUM_MAX]. The same unclamped psched_mtu() is assigned to q->cparams.mtu a bit below, and fq_codel_change() never updates it. codel_should_drop() tests "*backlog <= params->mtu"; with mtu == 0x80000000 (~2 GiB) and the default 32 MiB memory_limit, the test is always true, so CoDel is silently and completely disabled (no drops, no ECN). Declare a single clamped mtu and assign both q->quantum and q->cparams.mtu from it, which also removes the double psched_mtu() call. Conditions to recreate the bug: a device whose MTU (plus hard_header_len) wraps psched_mtu() into the sign bit (e.g. a dummy device with max_mtu == 0 accepting MTU 2147483634). Requires CAP_NET_ADMIN in a user namespace. The Linux kernel CVE team has assigned CVE-2026-90075 to this issue. Affected and fixed versions =========================== Issue introduced in 3.5 with commit 4b549a2ef4bef9965d97cbd992ba67930cd3e0fe and fixed in 5.10.270 with commit d315ee8a07fd1810880227319cf60e6cd925ef22 Issue introduced in 3.5 with commit 4b549a2ef4bef9965d97cbd992ba67930cd3e0fe and fixed in 5.15.221 with commit a9a5b2943a00df2ab81a2209f31dd9e87016f120 Issue introduced in 3.5 with commit 4b549a2ef4bef9965d97cbd992ba67930cd3e0fe and fixed in 6.1.188 with commit 3782067ec0d485628b6f1f9ede3eeeb4f611fcf2 Issue introduced in 3.5 with commit 4b549a2ef4bef9965d97cbd992ba67930cd3e0fe and fixed in 6.6.157 with commit 397e2b1f71d9f15b8b4e47d24eb620e4dff8878d Issue introduced in 3.5 with commit 4b549a2ef4bef9965d97cbd992ba67930cd3e0fe and fixed in 6.12.110 with commit 324f86806673ae4a55f66d28db84577f46f615e1 Issue introduced in 3.5 with commit 4b549a2ef4bef9965d97cbd992ba67930cd3e0fe and fixed in 6.18.52 with commit dfb4b61db886917244284b18b44b23d2254b82c2 Issue introduced in 3.5 with commit 4b549a2ef4bef9965d97cbd992ba67930cd3e0fe and fixed in 7.2.6 with commit 9f499e5827fdb6d7fdb46a7ce731852f6b1a1bb9 Issue introduced in 3.5 with commit 4b549a2ef4bef9965d97cbd992ba67930cd3e0fe and fixed in 7.3-rc1 with commit d9ebd8f9aa8b2773235889cb903fafd61f2d8585 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-2026-90075 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: net/sched/sch_fq_codel.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/d315ee8a07fd1810880227319cf60e6cd925ef22 https://git.kernel.org/stable/c/a9a5b2943a00df2ab81a2209f31dd9e87016f120 https://git.kernel.org/stable/c/3782067ec0d485628b6f1f9ede3eeeb4f611fcf2 https://git.kernel.org/stable/c/397e2b1f71d9f15b8b4e47d24eb620e4dff8878d https://git.kernel.org/stable/c/324f86806673ae4a55f66d28db84577f46f615e1 https://git.kernel.org/stable/c/dfb4b61db886917244284b18b44b23d2254b82c2 https://git.kernel.org/stable/c/9f499e5827fdb6d7fdb46a7ce731852f6b1a1bb9 https://git.kernel.org/stable/c/d9ebd8f9aa8b2773235889cb903fafd61f2d8585