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 7F6C418DB24; Mon, 10 Mar 2025 17:37:42 +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=1741628262; cv=none; b=Dq4PuxNgbWBlqSnnrET3Vi+CJUB/u6yBLgadSa/E7w9plmLD3mkDFc1D3Xu4u7XGnSUMKQaBnOqVzypUM6tjPrx1XoDpIHBsBd9dYERwyhnVOeUITyqgkuYMX4GljavrFHtK/zq5Cg9azv7Ld4yhfhcc4DFSKWwBzaK4seqAsUc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741628262; c=relaxed/simple; bh=dR/6ucvQRud9yG7lMtOHsX6Zx0QNayXgGDN3BPzisH8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=NxsG+Y9i2UHWZbAsFZ96Uzn/3QbXcoriGWTNqX2zscHvVg2HiZudvLeIH9J65t9d1I3dbQ7k2gePUrgJFo2jofX7lyR7X/AHS0TxFmSBFCsD8kHZRA5W6KtfgroyybeixwEp4ABMFyKjj8pZTymuNVlTrSayJSiqLqzg5OMN90A= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=t7W2pgRJ; 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="t7W2pgRJ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 04DB4C4CEE5; Mon, 10 Mar 2025 17:37:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1741628262; bh=dR/6ucvQRud9yG7lMtOHsX6Zx0QNayXgGDN3BPzisH8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=t7W2pgRJ9rqmJpzC3/eq4TYtxrNJBghSiOH+L/FfM3l9T92SJHzj9LKeDQJ7/wZxH YfbrXjvPi00w30twl9ELec6ia58mMRJLn3Bqkztyg6Ngj4bU8CoYldm5T4ERTbzEqP FF6vwxyo2b5dgvw8LSDQ3aKYgISPiGi1Q+jlCz24= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Quang Le , Cong Wang , Jakub Kicinski Subject: [PATCH 6.6 144/145] pfifo_tail_enqueue: Drop new packet when sch->limit == 0 Date: Mon, 10 Mar 2025 18:07:18 +0100 Message-ID: <20250310170440.567135754@linuxfoundation.org> X-Mailer: git-send-email 2.48.1 In-Reply-To: <20250310170434.733307314@linuxfoundation.org> References: <20250310170434.733307314@linuxfoundation.org> User-Agent: quilt/0.68 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Quang Le commit 647cef20e649c576dff271e018d5d15d998b629d upstream. Expected behaviour: In case we reach scheduler's limit, pfifo_tail_enqueue() will drop a packet in scheduler's queue and decrease scheduler's qlen by one. Then, pfifo_tail_enqueue() enqueue new packet and increase scheduler's qlen by one. Finally, pfifo_tail_enqueue() return `NET_XMIT_CN` status code. Weird behaviour: In case we set `sch->limit == 0` and trigger pfifo_tail_enqueue() on a scheduler that has no packet, the 'drop a packet' step will do nothing. This means the scheduler's qlen still has value equal 0. Then, we continue to enqueue new packet and increase scheduler's qlen by one. In summary, we can leverage pfifo_tail_enqueue() to increase qlen by one and return `NET_XMIT_CN` status code. The problem is: Let's say we have two qdiscs: Qdisc_A and Qdisc_B. - Qdisc_A's type must have '->graft()' function to create parent/child relationship. Let's say Qdisc_A's type is `hfsc`. Enqueue packet to this qdisc will trigger `hfsc_enqueue`. - Qdisc_B's type is pfifo_head_drop. Enqueue packet to this qdisc will trigger `pfifo_tail_enqueue`. - Qdisc_B is configured to have `sch->limit == 0`. - Qdisc_A is configured to route the enqueued's packet to Qdisc_B. Enqueue packet through Qdisc_A will lead to: - hfsc_enqueue(Qdisc_A) -> pfifo_tail_enqueue(Qdisc_B) - Qdisc_B->q.qlen += 1 - pfifo_tail_enqueue() return `NET_XMIT_CN` - hfsc_enqueue() check for `NET_XMIT_SUCCESS` and see `NET_XMIT_CN` => hfsc_enqueue() don't increase qlen of Qdisc_A. The whole process lead to a situation where Qdisc_A->q.qlen == 0 and Qdisc_B->q.qlen == 1. Replace 'hfsc' with other type (for example: 'drr') still lead to the same problem. This violate the design where parent's qlen should equal to the sum of its childrens'qlen. Bug impact: This issue can be used for user->kernel privilege escalation when it is reachable. Fixes: 57dbb2d83d10 ("sched: add head drop fifo queue") Reported-by: Quang Le Signed-off-by: Quang Le Signed-off-by: Cong Wang Link: https://patch.msgid.link/20250204005841.223511-2-xiyou.wangcong@gmail.com Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman --- net/sched/sch_fifo.c | 3 +++ 1 file changed, 3 insertions(+) --- a/net/sched/sch_fifo.c +++ b/net/sched/sch_fifo.c @@ -39,6 +39,9 @@ static int pfifo_tail_enqueue(struct sk_ { unsigned int prev_backlog; + if (unlikely(sch->limit == 0)) + return qdisc_drop(skb, sch, to_free); + if (likely(sch->q.qlen < sch->limit)) return qdisc_enqueue_tail(skb, sch);