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 965C92F83A0; Wed, 20 May 2026 17:51:06 +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=1779299467; cv=none; b=XuYuZGXesHi3njW5LKCNUsj0lDknd1eQemhKT3h3+YzJn37mfAWRlhe7N4pbqZa3mpj39T0sMGVzWvvLb2xgTSMOZCSKBWOcpt5NS/qFuaSDPD4uJq7fZIkwGF+06M/SbqtMGXWcWpI5kIWO+0uHxbZh3xJgKSLY7NkFWV7XNpA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779299467; c=relaxed/simple; bh=OBzlsAVCVSTiz8mJOdRvoYezIRcst+3JLJ7Eq6jsMWM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=X/YjTzYTCoq3b7mRJHUTxbW0D0CwPAFbZeG8uWSXkgWqbI1hcwbd2UxIvF2IYg0rOHuke1AjTBoeOFXcdQwu6NNLCKT2+BvQcHIdoQkzD646+wrcxTGXmw4tJZVxwoFdhxWiHV3DmibjdPcuSbNp1ZYVPIhXRr+kUDpwb2HRHmQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=BO9b9Var; 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="BO9b9Var" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A740D1F000E9; Wed, 20 May 2026 17:51:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1779299466; bh=uZj2m6m9LJVPdFIcwMmGjtGwlWIK2bgwabMplpPMuoU=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=BO9b9VarIOtZDhvqoIyOU1sk18gugoK13335aHL3YvnzaKPzpryfgDvGO9Wd1H6ZD KmOtZ/5lQJs23Rz5EvPjOzKTjKGh213dNezcRT5lPXgPqlY40JlLXvRX3HFoA2hbKl vbY9tv/WKMa8HSPBch1uwcB+Dg3zcgMpITs0g9IQ= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Xiang Mei , Weiming Shi , Jamal Hadi Salim , Jakub Kicinski , Sasha Levin Subject: [PATCH 6.18 782/957] net/sched: taprio: fix NULL pointer dereference in class dump Date: Wed, 20 May 2026 18:21:05 +0200 Message-ID: <20260520162151.519347485@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260520162134.554764788@linuxfoundation.org> References: <20260520162134.554764788@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 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Weiming Shi [ Upstream commit 3d07ca5c0fae311226f737963984bd94bb159a87 ] When a TAPRIO child qdisc is deleted via RTM_DELQDISC, taprio_graft() is called with new == NULL and stores NULL into q->qdiscs[cl - 1]. Subsequent RTM_GETTCLASS dump operations walk all classes via taprio_walk() and call taprio_dump_class(), which calls taprio_leaf() returning the NULL pointer, then dereferences it to read child->handle, causing a kernel NULL pointer dereference. The bug is reachable with namespace-scoped CAP_NET_ADMIN on any kernel with CONFIG_NET_SCH_TAPRIO enabled. On systems with unprivileged user namespaces enabled, an unprivileged local user can trigger a kernel panic by creating a taprio qdisc inside a new network namespace, grafting an explicit child qdisc, deleting it, and requesting a class dump. The RTM_GETTCLASS dump itself requires no capability. Oops: general protection fault, probably for non-canonical address 0xdffffc0000000007: 0000 [#1] SMP KASAN NOPTI KASAN: null-ptr-deref in range [0x0000000000000038-0x000000000000003f] RIP: 0010:taprio_dump_class (net/sched/sch_taprio.c:2478) Call Trace: tc_fill_tclass (net/sched/sch_api.c:1966) qdisc_class_dump (net/sched/sch_api.c:2326) taprio_walk (net/sched/sch_taprio.c:2514) tc_dump_tclass_qdisc (net/sched/sch_api.c:2352) tc_dump_tclass_root (net/sched/sch_api.c:2370) tc_dump_tclass (net/sched/sch_api.c:2431) rtnl_dumpit (net/core/rtnetlink.c:6864) netlink_dump (net/netlink/af_netlink.c:2325) rtnetlink_rcv_msg (net/core/rtnetlink.c:6959) netlink_rcv_skb (net/netlink/af_netlink.c:2550) Fix this by substituting &noop_qdisc when new is NULL in taprio_graft(), a common pattern used by other qdiscs (e.g., multiq_graft()) to ensure the q->qdiscs[] slots are never NULL. This makes control-plane dump paths safe without requiring individual NULL checks. Since the data-plane paths (taprio_enqueue and taprio_dequeue_from_txq) previously had explicit NULL guards that would drop/skip the packet cleanly, update those checks to test for &noop_qdisc instead. Without this, packets would reach taprio_enqueue_one() which increments the root qdisc's qlen and backlog before calling the child's enqueue; noop_qdisc drops the packet but those counters are never rolled back, permanently inflating the root qdisc's statistics. After this change *old can be a valid qdisc, NULL, or &noop_qdisc. Only call qdisc_put(*old) in the first case to avoid decreasing noop_qdisc's refcount, which was never increased. Fixes: 665338b2a7a0 ("net/sched: taprio: dump class stats for the actual q->qdiscs[]") Reported-by: Xiang Mei Signed-off-by: Weiming Shi Acked-by: Jamal Hadi Salim Tested-by: Weiming Shi Link: https://patch.msgid.link/20260422161958.2517539-3-bestswngs@gmail.com Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- net/sched/sch_taprio.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c index 91b85360f8091..b3481cafa6eca 100644 --- a/net/sched/sch_taprio.c +++ b/net/sched/sch_taprio.c @@ -633,7 +633,7 @@ static int taprio_enqueue(struct sk_buff *skb, struct Qdisc *sch, queue = skb_get_queue_mapping(skb); child = q->qdiscs[queue]; - if (unlikely(!child)) + if (unlikely(child == &noop_qdisc)) return qdisc_drop(skb, sch, to_free); if (taprio_skb_exceeds_queue_max_sdu(sch, skb)) { @@ -716,7 +716,7 @@ static struct sk_buff *taprio_dequeue_from_txq(struct Qdisc *sch, int txq, int len; u8 tc; - if (unlikely(!child)) + if (unlikely(child == &noop_qdisc)) return NULL; if (TXTIME_ASSIST_IS_ENABLED(q->flags)) @@ -2185,6 +2185,9 @@ static int taprio_graft(struct Qdisc *sch, unsigned long cl, if (!dev_queue) return -EINVAL; + if (!new) + new = &noop_qdisc; + if (dev->flags & IFF_UP) dev_deactivate(dev); @@ -2198,14 +2201,14 @@ static int taprio_graft(struct Qdisc *sch, unsigned long cl, *old = q->qdiscs[cl - 1]; if (FULL_OFFLOAD_IS_ENABLED(q->flags)) { WARN_ON_ONCE(dev_graft_qdisc(dev_queue, new) != *old); - if (new) + if (new != &noop_qdisc) qdisc_refcount_inc(new); - if (*old) + if (*old && *old != &noop_qdisc) qdisc_put(*old); } q->qdiscs[cl - 1] = new; - if (new) + if (new != &noop_qdisc) new->flags |= TCQ_F_ONETXQUEUE | TCQ_F_NOPARENT; if (dev->flags & IFF_UP) -- 2.53.0