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 BCC8F2E2850; Mon, 13 Apr 2026 16:44:51 +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=1776098691; cv=none; b=ClLq9peN79R/fGNxNz8p61b6MHh9Re5ANzdc5+Ro9drrmeccJqKUEZpOcl60TQsA0CgJSZRfMaaxUe1W5QAiVOdi5kf1PRmflWnlsKSTefNIlqJ2cJDxpVH5MlyVVhuIoM8NczF/+zblAwLZZeBuVH/S20QiJEqfw+GAbuSxuvg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776098691; c=relaxed/simple; bh=EdtrL/eR0hHYctOvUw1vz98ROOgWUsSa/bHDHMwcfm8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=U3uGv0K0xN2EuQHMzddMvVHE4Hhk+du4LaXagJ4sQoeY6kL8itl/EudZqPvUzXyH7CW5BXO5FjcIt7UCzF5WHe97OIELc+Ts8rsI0WkJv1BvWDxg8vgDcikI5hhUPErDbLvP9dm/pemTdce6noUrvYaqLdkkXItbeeM7hhCf7ew= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Zxa/L6WA; 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="Zxa/L6WA" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 52432C2BCAF; Mon, 13 Apr 2026 16:44:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1776098691; bh=EdtrL/eR0hHYctOvUw1vz98ROOgWUsSa/bHDHMwcfm8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Zxa/L6WARgpYmkk0h92ZqHlij19f84UG3P2x9tDjcJSt1Oss8AV1Y7z99BGpkOee1 4fUMrKOBhY1h52rwT7j1gvhFozJ2n4Js0U/jYHbK2XH+eBiKns0jEglil4c5WowtBU mhm3PUO4RK5af3VEkAOzruoZsaq9ttvpQHD4fV/s= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Ido Schimmel , syzbot+334190e097a98a1b81bb@syzkaller.appspotmail.com, Jiayuan Chen , David Ahern , Jakub Kicinski , Sasha Levin Subject: [PATCH 5.10 052/491] net: ipv6: fix panic when IPv4 route references loopback IPv6 nexthop Date: Mon, 13 Apr 2026 17:54:57 +0200 Message-ID: <20260413155820.999861396@linuxfoundation.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260413155819.042779211@linuxfoundation.org> References: <20260413155819.042779211@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jiayuan Chen [ Upstream commit 21ec92774d1536f71bdc90b0e3d052eff99cf093 ] When a standalone IPv6 nexthop object is created with a loopback device (e.g., "ip -6 nexthop add id 100 dev lo"), fib6_nh_init() misclassifies it as a reject route. This is because nexthop objects have no destination prefix (fc_dst=::), causing fib6_is_reject() to match any loopback nexthop. The reject path skips fib_nh_common_init(), leaving nhc_pcpu_rth_output unallocated. If an IPv4 route later references this nexthop, __mkroute_output() dereferences NULL nhc_pcpu_rth_output and panics. Simplify the check in fib6_nh_init() to only match explicit reject routes (RTF_REJECT) instead of using fib6_is_reject(). The loopback promotion heuristic in fib6_is_reject() is handled separately by ip6_route_info_create_nh(). After this change, the three cases behave as follows: 1. Explicit reject route ("ip -6 route add unreachable 2001:db8::/64"): RTF_REJECT is set, enters reject path, skips fib_nh_common_init(). No behavior change. 2. Implicit loopback reject route ("ip -6 route add 2001:db8::/32 dev lo"): RTF_REJECT is not set, takes normal path, fib_nh_common_init() is called. ip6_route_info_create_nh() still promotes it to reject afterward. nhc_pcpu_rth_output is allocated but unused, which is harmless. 3. Standalone nexthop object ("ip -6 nexthop add id 100 dev lo"): RTF_REJECT is not set, takes normal path, fib_nh_common_init() is called. nhc_pcpu_rth_output is properly allocated, fixing the crash when IPv4 routes reference this nexthop. Suggested-by: Ido Schimmel Fixes: 493ced1ac47c ("ipv4: Allow routes to use nexthop objects") Reported-by: syzbot+334190e097a98a1b81bb@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/698f8482.a70a0220.2c38d7.00ca.GAE@google.com/T/ Signed-off-by: Jiayuan Chen Reviewed-by: Ido Schimmel Reviewed-by: David Ahern Link: https://patch.msgid.link/20260304113817.294966-2-jiayuan.chen@linux.dev Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- net/ipv6/route.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) diff --git a/net/ipv6/route.c b/net/ipv6/route.c index ac24f8b624e34..27736b5847378 100644 --- a/net/ipv6/route.c +++ b/net/ipv6/route.c @@ -3408,7 +3408,6 @@ int fib6_nh_init(struct net *net, struct fib6_nh *fib6_nh, { struct net_device *dev = NULL; struct inet6_dev *idev = NULL; - int addr_type; int err; fib6_nh->fib_nh_family = AF_INET6; @@ -3449,11 +3448,10 @@ int fib6_nh_init(struct net *net, struct fib6_nh *fib6_nh, fib6_nh->fib_nh_weight = 1; - /* We cannot add true routes via loopback here, - * they would result in kernel looping; promote them to reject routes + /* Reset the nexthop device to the loopback device in case of reject + * routes. */ - addr_type = ipv6_addr_type(&cfg->fc_dst); - if (fib6_is_reject(cfg->fc_flags, dev, addr_type)) { + if (cfg->fc_flags & RTF_REJECT) { /* hold loopback dev/idev if we haven't done so. */ if (dev != net->loopback_dev) { if (dev) { -- 2.51.0