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 068394C9DE2; Thu, 17 Sep 2026 15:41:14 +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=1789659681; cv=none; b=GlW5KpgDwL/fWw2VvEmOOz0WrdbgEGawg2uuStzTkPShb0Hcbwnz2kc/MjWEzCKcHQAyA1dwQt7GvqrHxxxatuHFcyd01bHORAWGGnPWEM4cW41oC89ueMYna1rUd6iagK4xL7dp66ggZDHPxF6xPcHbxawmVWQnQ7kSdqqGaQQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789659681; c=relaxed/simple; bh=oJZag2H16CcUxV6/gl8QOKCGiDgcOxR2hVGLg4S8cmQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=KxfUCIA3QUTV22swyn8CK2JeLpkAD3j3gwt0FFSWMs8gpXsvy6LXk5o40opOdsiZ0yLOFp/JDS5qvZPp3GEp2wFd3gsSfiJeY8v8emniaYkkF4p8g1ItYhPtMlrTNKwwqBFcuX56veVjQ+E3DvBysoaqvmJrulYWKLZhtWMvjW8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=mcmYqw4u; 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="mcmYqw4u" Received: by smtp.kernel.org (Postfix) with ESMTPSA id AD0981F0089B; Thu, 17 Sep 2026 15:41:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1789659670; bh=buQg84XvSdjMtJyhluactRpdTw0PS8XZj01bJyMsIHU=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=mcmYqw4uMRj3xwfBM16U+uj1QUbejy4pnGAQ+6SVYUnI+lJNN6KGkyp86kXMEL2Wx +F4cO0nH/b8BAMn8RUwQNYLGT9tm6OVUaWK7MH4V1mtug/2uT+PXfNI0ZazXOhYTik dXTMKlPM3iJHtnqVomx1ab3dOoJe9Knh1Fa0yjLQ= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Vega , Victor Nogueira , Jamal Hadi Salim , Jakub Kicinski , Sasha Levin Subject: [PATCH 7.2 285/733] net: cap tx_queue_len at S16_MAX to prevent oversized ring allocations Date: Thu, 17 Sep 2026 16:09:53 +0100 Message-ID: <20260917151358.489781877@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260917151350.597953846@linuxfoundation.org> References: <20260917151350.597953846@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 7.2-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jamal Hadi Salim [ Upstream commit 66ab4c59b74db7ab53a1c9083feaaede393a96a0 ] Several subsystems allocate ring buffers sized by dev->tx_queue_len with no upper bound. An unprivileged user (via unshare -Urn) can set a huge tx_queue_len and exhaust global memory with ring allocations: - pfifo_fast: pfifo_fast_init() and pfifo_fast_change_tx_queue_len() allocate 3 skb_array rings of tx_queue_len entries each. - tun: tun_queue_resize() and the queue-attach path resize ptr_rings to tx_queue_len on the NETDEV_CHANGE_TX_QUEUE_LEN notifier. - tap (macvtap/ipvtap): tap_queue_resize() and tap_init() resize/init ptr_rings to tx_queue_len on the same notifier. netif_change_tx_queue_len() is the single entry point for IFLA_TXQLEN, sysfs, and the SIOCSIFTXQLEN ioctl. Cap new_len at S16_MAX (32767) there so the oversized value is rejected at set time. This takes effect whether the device is up or down, before dev->tx_queue_len is written, before any notifier fires, and before any ring is allocated. The "> S16_MAX" check also subsumes the previous unsigned-long truncation test, and a negative ifr_qlen from the ioctl lands far above the cap after conversion, so both old failure modes are covered by the one comparison. tx_queue_len is ambigious: both a per-ring sizing multiplier and a default queue-length/limit knob for consumers that allocate nothing at set time (pfifo/bfifo/gred/plug/sfb limits, htb direct_qlen, qfq max_classes, teql). 32767 is chosen as the largest value NLA_POLICY_FULL_RANGE can express for the u32 IFLA_TXQLEN policy in patch 2/3 while staying a legitimate queue length on high-BDP paths; the ring-memory trade-off of a shared knob is disclosed below. Conditions to recreate the bug: - CONFIG_NET_SCHED=y, CONFIG_VETH=y, CONFIG_USER_NS=y, CONFIG_NET_NS=y. - Unprivileged user in a fresh user+net namespace (unshare -Urn). - pfifo_fast: create veth pairs, set tx_queue_len to 500000, attach mq+pfifo_fast. ~28 iterations OOMs a 2GB guest. - tun: create 50 tun devices with IFF_MULTI_QUEUE, set tx_queue_len to 500000, open 8 queues each. ~1.6GB of ptr_ring allocations OOMs a 512MB guest. - tap: same as tun with IFF_TAP. ~960MB OOMs a 512MB guest. - On the fixed kernel the oversized tx_queue_len is rejected with -ERANGE at set time (all four paths: RTM_SETLINK, RTM_NEWLINK create, sysfs, ioctl - the latter two via this check, the former two via this check and the 2/3 parse policy respectively). Fixes: 6a643ddb5624 ("net: introduce helper dev_change_tx_queue_len()") Reported-by: Vega Closes: https://lore.kernel.org/netdev/20260828121902.66837-1-jhs@mojatatu.com/ Tested-by: Victor Nogueira Signed-off-by: Jamal Hadi Salim Link: https://patch.msgid.link/QDISC-2899.v2.20260901233641@mojatatu.com Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- net/core/dev.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/core/dev.c b/net/core/dev.c index 9ac8ac6004145..74dd9e25f4ff7 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -9932,7 +9932,7 @@ int netif_change_tx_queue_len(struct net_device *dev, unsigned long new_len) unsigned int orig_len = dev->tx_queue_len; int res; - if (new_len != (unsigned int)new_len) + if (new_len > S16_MAX) return -ERANGE; if (new_len != orig_len) { -- 2.53.0