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 A73312FA623; Tue, 17 Jun 2025 16:55:45 +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=1750179345; cv=none; b=Nz4qah+XoDK2QOccO1wAzMAfo336sCWvFoLy7tOCNniFZdsmNlXj5J9LWzO2jhSCNgLaCDIer0e76RTzNNiyEBKnpTTuFxPEAUhRmiQJY+fZMH9DcQBWYqJAEMhAQ8/mhOY1y79MT6WfbAt0kfXYNSLBh7OwBanT3Grpsw4S9+w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750179345; c=relaxed/simple; bh=oDRSFhxsjnsNrXGDeDKaDQbcDsPgzqCr2Tx1FpCZo+Y=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=uaANkOLSIKCfVNpUjlbWi7qh6c3JHS+VeVhgZZS5c6BfsMUAmbqcpv1hozt6prx2S+q3Gh2+GxKUpbERhf2J6dvQhT4saFz/yczeCjZAxgUd5i4YG7MrtuNKdUAScESzMPGuF/Stj7AjP9uznnF6pbl6kB0oAos/IXpyj+X/3Nk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Djd3W3bg; 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="Djd3W3bg" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 16B80C4CEE3; Tue, 17 Jun 2025 16:55:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1750179345; bh=oDRSFhxsjnsNrXGDeDKaDQbcDsPgzqCr2Tx1FpCZo+Y=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Djd3W3bgKCnNnkuWyTnqrpl1S2hU805aIK5TozbMB0vBDs/L8dpW04bj00m1ftYqA ca7N5fdoOMzAf7zxIiQgUGnuO5/W4Mp4DuSz6OUMtE+2KU4KH9puzNrrj2BzoeXk4G 0P+CSHrxAyMsW760VndzK/9kD3NGwAsDbBf2UYtQ= 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 6.15 718/780] net_sched: red: fix a race in __red_change() Date: Tue, 17 Jun 2025 17:27:06 +0200 Message-ID: <20250617152520.734465277@linuxfoundation.org> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250617152451.485330293@linuxfoundation.org> References: <20250617152451.485330293@linuxfoundation.org> User-Agent: quilt/0.68 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 6.15-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 1ba3e0bba54f0..4696c893cf553 100644 --- a/net/sched/sch_red.c +++ b/net/sched/sch_red.c @@ -285,7 +285,7 @@ static int __red_change(struct Qdisc *sch, struct nlattr **tb, q->userbits = userbits; 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