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 6FD6035334D; Tue, 26 Aug 2025 14:31:27 +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=1756218687; cv=none; b=GkgEfcQO4jqMiiCLnn6hH/balW1DlnFVkzYuIxHCPDUKfF3FxJBBV47K/AHqwfVgk3CwAelNac0RyiAmja2q0uyU7EpgDH9QhuZD1V2aDM+CAgJj+E9mv2i32/e/0N8bkOc614ia/fMwha3ZSuSXYI9prfIDWE07PoyiWzCoo10= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756218687; c=relaxed/simple; bh=224FsCw0glkEKzAQpwEBqOlYc0jFdGOEmxZGQvpB+fI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=t9zqc92rv9/afrmNnQpui80sJwN/CTUMP8OMYyf/e/PZhs13pOq+c67YgUtzr3407zIlBSf6o64SU1Tn1A3PtOdVk4kaD8ra6f3SJJkkHBE/oUxAFxJZiN4w3+DiCluxBpSXzB7Tc8hFpb8jdYiAwimgfX9gNAbTHIBl3cDwW2w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=LCDXNeZc; 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="LCDXNeZc" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A2764C4CEF1; Tue, 26 Aug 2025 14:31:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1756218687; bh=224FsCw0glkEKzAQpwEBqOlYc0jFdGOEmxZGQvpB+fI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=LCDXNeZcjlf21UItijs2u7hfHE130OtAnmJpdaMWq9v9J4djBd6igfFNqR3mZX55A 6Z4vnNVkXX35f9QYKnh1DjhGysCXMq/D5iNC+hNNElA4b/kNvQqH1heSEginVW5hX3 s3+QPG/UismEfPfFcAQ3av0aijd++mNXDOlY/Kcs= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, William Liu , Savino Dicanosa , Jamal Hadi Salim , Jakub Kicinski , Sasha Levin Subject: [PATCH 5.4 095/403] net/sched: Restrict conditions for adding duplicating netems to qdisc tree Date: Tue, 26 Aug 2025 13:07:01 +0200 Message-ID: <20250826110909.295658748@linuxfoundation.org> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20250826110905.607690791@linuxfoundation.org> References: <20250826110905.607690791@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 5.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: William Liu [ Upstream commit ec8e0e3d7adef940cdf9475e2352c0680189d14e ] netem_enqueue's duplication prevention logic breaks when a netem resides in a qdisc tree with other netems - this can lead to a soft lockup and OOM loop in netem_dequeue, as seen in [1]. Ensure that a duplicating netem cannot exist in a tree with other netems. Previous approaches suggested in discussions in chronological order: 1) Track duplication status or ttl in the sk_buff struct. Considered too specific a use case to extend such a struct, though this would be a resilient fix and address other previous and potential future DOS bugs like the one described in loopy fun [2]. 2) Restrict netem_enqueue recursion depth like in act_mirred with a per cpu variable. However, netem_dequeue can call enqueue on its child, and the depth restriction could be bypassed if the child is a netem. 3) Use the same approach as in 2, but add metadata in netem_skb_cb to handle the netem_dequeue case and track a packet's involvement in duplication. This is an overly complex approach, and Jamal notes that the skb cb can be overwritten to circumvent this safeguard. 4) Prevent the addition of a netem to a qdisc tree if its ancestral path contains a netem. However, filters and actions can cause a packet to change paths when re-enqueued to the root from netem duplication, leading us to the current solution: prevent a duplicating netem from inhabiting the same tree as other netems. [1] https://lore.kernel.org/netdev/8DuRWwfqjoRDLDmBMlIfbrsZg9Gx50DHJc1ilxsEBNe2D6NMoigR_eIRIG0LOjMc3r10nUUZtArXx4oZBIdUfZQrwjcQhdinnMis_0G7VEk=@willsroot.io/ [2] https://lwn.net/Articles/719297/ Fixes: 0afb51e72855 ("[PKT_SCHED]: netem: reinsert for duplication") Reported-by: William Liu Reported-by: Savino Dicanosa Signed-off-by: William Liu Signed-off-by: Savino Dicanosa Acked-by: Jamal Hadi Salim Link: https://patch.msgid.link/20250708164141.875402-1-will@willsroot.io Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- net/sched/sch_netem.c | 40 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 40 insertions(+) diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c index 27bd18c74e85..cdf2df194d24 100644 --- a/net/sched/sch_netem.c +++ b/net/sched/sch_netem.c @@ -962,6 +962,41 @@ static int parse_attr(struct nlattr *tb[], int maxtype, struct nlattr *nla, return 0; } +static const struct Qdisc_class_ops netem_class_ops; + +static int check_netem_in_tree(struct Qdisc *sch, bool duplicates, + struct netlink_ext_ack *extack) +{ + struct Qdisc *root, *q; + unsigned int i; + + root = qdisc_root_sleeping(sch); + + if (sch != root && root->ops->cl_ops == &netem_class_ops) { + if (duplicates || + ((struct netem_sched_data *)qdisc_priv(root))->duplicate) + goto err; + } + + if (!qdisc_dev(root)) + return 0; + + hash_for_each(qdisc_dev(root)->qdisc_hash, i, q, hash) { + if (sch != q && q->ops->cl_ops == &netem_class_ops) { + if (duplicates || + ((struct netem_sched_data *)qdisc_priv(q))->duplicate) + goto err; + } + } + + return 0; + +err: + NL_SET_ERR_MSG(extack, + "netem: cannot mix duplicating netems with other netems in tree"); + return -EINVAL; +} + /* Parse netlink message to set options */ static int netem_change(struct Qdisc *sch, struct nlattr *opt, struct netlink_ext_ack *extack) @@ -1023,6 +1058,11 @@ static int netem_change(struct Qdisc *sch, struct nlattr *opt, q->gap = qopt->gap; q->counter = 0; q->loss = qopt->loss; + + ret = check_netem_in_tree(sch, qopt->duplicate, extack); + if (ret) + goto unlock; + q->duplicate = qopt->duplicate; /* for compatibility with earlier versions. -- 2.39.5