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 DEB58253B60; Mon, 23 Jun 2025 13:28:33 +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=1750685314; cv=none; b=EeDn2vK5AX95JXcE3Z9nvhhIcgVl12HG2UYPihp2V7lhY8LAlqnQfspias5w63PziiPbH4s9uAfs0bIEmtBZEfzZY7iKfVUzbUoRcj1Fr/YpZGR40xMkjzFjm56rrZFFl3PZ8aJMbRaQpsBFNrvysswn2fAf8nr2HdN4+0knk9I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750685314; c=relaxed/simple; bh=ug1azJou2Qd8L8Ahmi8cjcAJzxKhZwmxIrrNPh53nfY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=fVRJTb3Aa0sh59hqCW77ivkzyonRGEPgM/qBuSvGwAQYSJHib3nEvgcQHUzVILOnT0L45L8Kle15abKLkIYRVu1+mgd/+WgyV/7+gE/txY/bTMJk4RYOH2PzE1ceOcmbcJUdv7XfOkUpeTlXefhahXkFb0QFP3v9X1EaDaIktOI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=VUDrA/eZ; 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="VUDrA/eZ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2CF74C4CEF1; Mon, 23 Jun 2025 13:28:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1750685313; bh=ug1azJou2Qd8L8Ahmi8cjcAJzxKhZwmxIrrNPh53nfY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=VUDrA/eZUvprp0z/+AffM6HTt4271gr5G060Kmw7US1QmZYhmXduKie1rzU6A6FWK yJUfY4CKmDSMldzCgeWNuLRD7z+XevE7y3cPMcXRcQjIooVBUybR+Yd6K/qbkKHCaf h+e355uPw9rEinj6WFQttPdRimVZMhb9vqHXoysU= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Gerrard Tai , Eric Dumazet , Jakub Kicinski , Sasha Levin Subject: [PATCH 5.4 084/222] net_sched: red: fix a race in __red_change() Date: Mon, 23 Jun 2025 15:06:59 +0200 Message-ID: <20250623130614.624359584@linuxfoundation.org> X-Mailer: git-send-email 2.50.0 In-Reply-To: <20250623130611.896514667@linuxfoundation.org> References: <20250623130611.896514667@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 5.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Eric Dumazet [ Upstream commit 85a3e0ede38450ea3053b8c45d28cf55208409b8 ] Gerrard Tai reported a race condition in RED, whenever SFQ perturb timer fires at the wrong time. The race is as follows: CPU 0 CPU 1 [1]: lock root [2]: qdisc_tree_flush_backlog() [3]: unlock root | | [5]: lock root | [6]: rehash | [7]: qdisc_tree_reduce_backlog() | [4]: qdisc_put() This can be abused to underflow a parent's qlen. Calling qdisc_purge_queue() instead of qdisc_tree_flush_backlog() should fix the race, because all packets will be purged from the qdisc before releasing the lock. Fixes: 0c8d13ac9607 ("net: sched: red: delay destroying child qdisc on replace") Reported-by: Gerrard Tai Suggested-by: Gerrard Tai Signed-off-by: Eric Dumazet Link: https://patch.msgid.link/20250611111515.1983366-3-edumazet@google.com Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- net/sched/sch_red.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/sched/sch_red.c b/net/sched/sch_red.c index 476853ff69894..64532ee591a96 100644 --- a/net/sched/sch_red.c +++ b/net/sched/sch_red.c @@ -235,7 +235,7 @@ static int red_change(struct Qdisc *sch, struct nlattr *opt, q->flags = ctl->flags; q->limit = ctl->limit; if (child) { - qdisc_tree_flush_backlog(q->qdisc); + qdisc_purge_queue(q->qdisc); old_child = q->qdisc; q->qdisc = child; } -- 2.39.5