From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.uniroma2.it (smtp.uniroma2.it [160.80.4.37]) by smtp.subspace.kernel.org (Postfix) with ESMTP id A074B42A141; Mon, 17 Aug 2026 13:28:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=160.80.4.37 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786973338; cv=none; b=SwvgApOzYh6VwksrqOO4P1R2O1vXPp56tPekEQFIzvsu9cC+bNk4rV2njF9U4THfCvhsx78vUw3ZcdYBBuUpmJpg8SHbUlSP6SKrANsvWS07y4xq4NTumzP120YHH02sCn8LtWWcdo2w+uaR/zBBnT4mp60yKZ/XYYZ9Z4XIDIE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786973338; c=relaxed/simple; bh=ECnA9N6J6yvXElKohPbOxCBbjQKGS74I1vdWAggDW8c=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=gC9wWpkZpiAj3JAYJChvNoULhDIqkuKFq4XQTWU4BIK20lp1mVTKLgOu8YcVQPi+xF5whxkI1eo6nwkH3Jgpr8BTb7P2T4JGIMJocO0JitnfF+n+AhTJZ2W10P1gPVEUiO6CWQb8jfh2P5zlV2jRgffE89kHZTP+FITOSB+DH68= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=uniroma2.it; spf=pass smtp.mailfrom=uniroma2.it; arc=none smtp.client-ip=160.80.4.37 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=uniroma2.it Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=uniroma2.it Received: from localhost.localdomain ([160.80.103.126]) by smtp-2015.uniroma2.it (8.14.4/8.14.4/Debian-8) with ESMTP id 67HDSDVD004409; Mon, 17 Aug 2026 15:28:18 +0200 From: Andrea Mayer To: netdev@vger.kernel.org Cc: linux-kernel@vger.kernel.org, dsahern@kernel.org, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, idosch@nvidia.com, alex.aring@gmail.com, justin.iurman@gmail.com, bestswngs@gmail.com, stefano.salsano@uniroma2.it, xmei5@asu.edu, Andrea Mayer , stable@vger.kernel.org Subject: [PATCH net v3] ipv6: rpl: fix NULL dereference of idev in ipv6_rpl_srh_rcv() Date: Mon, 17 Aug 2026 15:26:44 +0200 Message-Id: <20260817132644.2223-1-andrea.mayer@uniroma2.it> X-Mailer: git-send-email 2.20.1 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Virus-Scanned: clamav-milter 0.100.0 at smtp-2015 X-Virus-Status: Clean ipv6_rpl_srh_rcv() dereferences idev from __in6_dev_get() without a NULL check when reading idev->cnf.rpl_seg_enabled. When the device's MTU drops below IPV6_MIN_MTU, addrconf_ifdown() clears dev->ip6_ptr through RCU_INIT_POINTER(). A packet that passed the idev check in ip6_rcv_core() can then reach ipv6_rpl_srh_rcv() with dev->ip6_ptr already NULL. Reproduced by flooding the receiving interface with ping6 traffic while flapping its MTU between 1500 and 1200: BUG: KASAN: null-ptr-deref in ipv6_rpl_srh_rcv+0xb3/0x1070 Read of size 4 at addr 00000000000006b4 by task ping6/394 CPU: 2 UID: 0 PID: 394 Comm: ping6 Not tainted 7.2.0-rc7-micro-vm-dev-00095-g24ef02f934ee #240 PREEMPT(full) Call Trace: kasan_report+0xc6/0x100 ipv6_rpl_srh_rcv+0xb3/0x1070 ip6_protocol_deliver_rcu+0x759/0x9a0 ip6_input_finish+0xa8/0x1b0 ip6_input+0xe1/0x490 ipv6_rcv+0x33d/0x460 __netif_receive_skb_one_core+0xd6/0x130 process_backlog+0x2cc/0xa00 __napi_poll.constprop.0+0x56/0x270 net_rx_action+0x327/0x730 handle_softirqs+0x11e/0x630 do_softirq+0xb3/0xf0 Both ipv6_rpl_srh_rcv() and ipv6_srh_rcv() are called only from ipv6_rthdr_rcv(), which already has an idev lookup. Fix the NULL dereference on the RPL path by checking idev in ipv6_rthdr_rcv(), before it calls either function. The callees take idev as an argument and no longer call __in6_dev_get(), so the packet is now dropped in one place, with SKB_DROP_REASON_IPV6DISABLED on both paths. Fixes: 8610c7c6e3bd ("net: ipv6: add support for rpl sr exthdr") Cc: stable@vger.kernel.org Signed-off-by: Andrea Mayer Tested-by: Xiang Mei --- v3: - move the idev NULL check into ipv6_rthdr_rcv() and use the same drop reason on the seg6 and RPL paths (David Ahern) - pass idev to ipv6_srh_rcv() and ipv6_rpl_srh_rcv(), and check it for NULL in ipv6_rthdr_rcv() only for the seg6 and RPL types - add Xiang Mei's Tested-by tag v2: https://lore.kernel.org/netdev/20260518140630.24280-1-andrea.mayer@uniroma2.it/ - use SKB_DROP_REASON_IPV6DISABLED as drop reason (Eric Dumazet) v1: https://lore.kernel.org/netdev/20260428224816.11223-1-andrea.mayer@uniroma2.it/ --- net/ipv6/exthdrs.c | 26 ++++++++++++-------------- 1 file changed, 12 insertions(+), 14 deletions(-) diff --git a/net/ipv6/exthdrs.c b/net/ipv6/exthdrs.c index 9c677eb1d1a6..51941ad656a3 100644 --- a/net/ipv6/exthdrs.c +++ b/net/ipv6/exthdrs.c @@ -368,23 +368,16 @@ static void seg6_update_csum(struct sk_buff *skb) (__be32 *)addr); } -static int ipv6_srh_rcv(struct sk_buff *skb) +static int ipv6_srh_rcv(struct sk_buff *skb, struct inet6_dev *idev) { struct inet6_skb_parm *opt = IP6CB(skb); struct net *net = dev_net(skb->dev); struct ipv6_sr_hdr *hdr; - struct inet6_dev *idev; struct in6_addr *addr; int accept_seg6; hdr = (struct ipv6_sr_hdr *)skb_transport_header(skb); - idev = __in6_dev_get(skb->dev); - if (!idev) { - kfree_skb(skb); - return -1; - } - accept_seg6 = min(READ_ONCE(net->ipv6.devconf_all->seg6_enabled), READ_ONCE(idev->cnf.seg6_enabled)); @@ -485,12 +478,11 @@ static int ipv6_srh_rcv(struct sk_buff *skb) return -1; } -static int ipv6_rpl_srh_rcv(struct sk_buff *skb) +static int ipv6_rpl_srh_rcv(struct sk_buff *skb, struct inet6_dev *idev) { struct ipv6_rpl_sr_hdr *hdr, *ohdr, *chdr; struct inet6_skb_parm *opt = IP6CB(skb); struct net *net = dev_net(skb->dev); - struct inet6_dev *idev; struct ipv6hdr *oldhdr; unsigned int chdr_len; unsigned char *buf; @@ -499,8 +491,6 @@ static int ipv6_rpl_srh_rcv(struct sk_buff *skb) u64 n = 0; u32 r; - idev = __in6_dev_get(skb->dev); - accept_rpl_seg = min(READ_ONCE(net->ipv6.devconf_all->rpl_seg_enabled), READ_ONCE(idev->cnf.rpl_seg_enabled)); if (!accept_rpl_seg) { @@ -689,10 +679,14 @@ static int ipv6_rthdr_rcv(struct sk_buff *skb) switch (hdr->type) { case IPV6_SRCRT_TYPE_4: /* segment routing */ - return ipv6_srh_rcv(skb); + if (!idev) + goto disabled; + return ipv6_srh_rcv(skb, idev); case IPV6_SRCRT_TYPE_3: /* rpl segment routing */ - return ipv6_rpl_srh_rcv(skb); + if (!idev) + goto disabled; + return ipv6_rpl_srh_rcv(skb, idev); default: break; } @@ -837,6 +831,10 @@ static int ipv6_rthdr_rcv(struct sk_buff *skb) icmpv6_param_prob(skb, ICMPV6_HDR_FIELD, (&hdr->type) - skb_network_header(skb)); return -1; + +disabled: + kfree_skb_reason(skb, SKB_DROP_REASON_IPV6DISABLED); + return -1; } static const struct inet6_protocol rthdr_protocol = { -- 2.43.0