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 A2F083D75CE for ; Mon, 4 May 2026 12:48:23 +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=1777898903; cv=none; b=N8i2ZIVYxxQEZJNURHz/5zhc2xR0C8zjDM9rPHN8BAKBZBPGyOukQ/z54s0Brg08EAilQbVVT0hsicYx4QPsySSLeX8XpNkQlbSvvtjyVYdg4GVkHvo2+LstSQbNiDM/u1FLXKMfoD8/xkVK/Oxnr0xCIYJFTWMYJJzPJg7k9BA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777898903; c=relaxed/simple; bh=2rN9MV4DMZX60Eoit0aai/SthA6dZ5VP5jBNBnOx4o8=; h=Subject:To:Cc:From:Date:Message-ID:MIME-Version:Content-Type; b=RmJm7+eZzlXrkUs2XhkVFBAHaJurBFgQFzxfvE9Wdod7ZAl5VWjRKtUM0+EBlsu/n1hyl4lMIwbJZ4EpNeQacQWt+XT2ywzddjs/CPGWNJiMZsNaj4LHAObMb9wAbfi55WpiZEL8EP9ZNBqgXhLAx30cXGwcC5DBspm+2KdUtGg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=h7Zk7TFD; 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="h7Zk7TFD" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C1EFDC2BCB8; Mon, 4 May 2026 12:48:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1777898903; bh=2rN9MV4DMZX60Eoit0aai/SthA6dZ5VP5jBNBnOx4o8=; h=Subject:To:Cc:From:Date:From; b=h7Zk7TFDqlxCfeXvjatCJl17E5GkvN341x5O91+mKxGAxfSrEmThtTrOsCLn3Axf1 tXtdHZWLyekMUPdRW0lTjP8SQwy8w4ptz2acaPKg3KhpoXkdZFM+1GsmPlGs+NPODw l+Jimx/ldejSyOk0fGXxO1P6FqHW4vUFgmJGky1I= Subject: FAILED: patch "[PATCH] net: ipv6: fix NOREF dst use in seg6 and rpl lwtunnels" failed to apply to 5.10-stable tree To: andrea.mayer@uniroma2.it,horms@kernel.org,justin.iurman@gmail.com,pabeni@redhat.com Cc: From: Date: Mon, 04 May 2026 14:48:20 +0200 Message-ID: <2026050420-privacy-dotted-7b6c@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit The patch below does not apply to the 5.10-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.10.y git checkout FETCH_HEAD git cherry-pick -x f9c52a6ba9780bd27e0bf4c044fd91c13c778b6e # git commit -s git send-email --to '' --in-reply-to '2026050420-privacy-dotted-7b6c@gregkh' --subject-prefix 'PATCH 5.10.y' HEAD^.. Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From f9c52a6ba9780bd27e0bf4c044fd91c13c778b6e Mon Sep 17 00:00:00 2001 From: Andrea Mayer Date: Tue, 21 Apr 2026 11:47:35 +0200 Subject: [PATCH] net: ipv6: fix NOREF dst use in seg6 and rpl lwtunnels seg6_input_core() and rpl_input() call ip6_route_input() which sets a NOREF dst on the skb, then pass it to dst_cache_set_ip6() invoking dst_hold() unconditionally. On PREEMPT_RT, ksoftirqd is preemptible and a higher-priority task can release the underlying pcpu_rt between the lookup and the caching through a concurrent FIB lookup on a shared nexthop. Simplified race sequence: ksoftirqd/X higher-prio task (same CPU X) ----------- -------------------------------- seg6_input_core(,skb)/rpl_input(skb) dst_cache_get() -> miss ip6_route_input(skb) -> ip6_pol_route(,skb,flags) [RT6_LOOKUP_F_DST_NOREF in flags] -> FIB lookup resolves fib6_nh [nhid=N route] -> rt6_make_pcpu_route() [creates pcpu_rt, refcount=1] pcpu_rt->sernum = fib6_sernum [fib6_sernum=W] -> cmpxchg(fib6_nh.rt6i_pcpu, NULL, pcpu_rt) [slot was empty, store succeeds] -> skb_dst_set_noref(skb, dst) [dst is pcpu_rt, refcount still 1] rt_genid_bump_ipv6() -> bumps fib6_sernum [fib6_sernum from W to Z] ip6_route_output() -> ip6_pol_route() -> FIB lookup resolves fib6_nh [nhid=N] -> rt6_get_pcpu_route() pcpu_rt->sernum != fib6_sernum [W <> Z, stale] -> prev = xchg(rt6i_pcpu, NULL) -> dst_release(prev) [prev is pcpu_rt, refcount 1->0, dead] dst = skb_dst(skb) [dst is the dead pcpu_rt] dst_cache_set_ip6(dst) -> dst_hold() on dead dst -> WARN / use-after-free For the race to occur, ksoftirqd must be preemptible (PREEMPT_RT without PREEMPT_RT_NEEDS_BH_LOCK) and a concurrent task must be able to release the pcpu_rt. Shared nexthop objects provide such a path, as two routes pointing to the same nhid share the same fib6_nh and its rt6i_pcpu entry. Fix seg6_input_core() and rpl_input() by calling skb_dst_force() after ip6_route_input() to force the NOREF dst into a refcounted one before caching. The output path is not affected as ip6_route_output() already returns a refcounted dst. Fixes: af4a2209b134 ("ipv6: sr: use dst_cache in seg6_input") Fixes: a7a29f9c361f ("net: ipv6: add rpl sr tunnel") Cc: stable@vger.kernel.org Signed-off-by: Andrea Mayer Reviewed-by: Simon Horman Reviewed-by: Justin Iurman Link: https://patch.msgid.link/20260421094735.20997-1-andrea.mayer@uniroma2.it Signed-off-by: Paolo Abeni diff --git a/net/ipv6/rpl_iptunnel.c b/net/ipv6/rpl_iptunnel.c index c7942cf65567..4e10adcd70e8 100644 --- a/net/ipv6/rpl_iptunnel.c +++ b/net/ipv6/rpl_iptunnel.c @@ -287,7 +287,16 @@ static int rpl_input(struct sk_buff *skb) if (!dst) { ip6_route_input(skb); + + /* ip6_route_input() sets a NOREF dst; force a refcount on it + * before caching or further use. + */ + skb_dst_force(skb); dst = skb_dst(skb); + if (unlikely(!dst)) { + err = -ENETUNREACH; + goto drop; + } /* cache only if we don't create a dst reference loop */ if (!dst->error && lwtst != dst->lwtstate) { diff --git a/net/ipv6/seg6_iptunnel.c b/net/ipv6/seg6_iptunnel.c index 9b64343ebad6..4c45c0a77d75 100644 --- a/net/ipv6/seg6_iptunnel.c +++ b/net/ipv6/seg6_iptunnel.c @@ -515,7 +515,16 @@ static int seg6_input_core(struct net *net, struct sock *sk, if (!dst) { ip6_route_input(skb); + + /* ip6_route_input() sets a NOREF dst; force a refcount on it + * before caching or further use. + */ + skb_dst_force(skb); dst = skb_dst(skb); + if (unlikely(!dst)) { + err = -ENETUNREACH; + goto drop; + } /* cache only if we don't create a dst reference loop */ if (!dst->error && lwtst != dst->lwtstate) {