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 E0C1B33A9CF; Thu, 12 Mar 2026 20:27:14 +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=1773347235; cv=none; b=s51HaQlkNnQp4/FP3/U/7CzE638O2FO5ccvx/jZ6jZ9l5D0IIY16eBWiU4aOxBSGXRLx0aMy0Ww/CvTMMDnAObuiAoKsBks88bAtImavH4F5/5ZaL8ohY9Jf2mrEjcWY40pqPcL1Rt63kbnLk39KQGqh3Te6nlWouQMRV3GC+fM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773347235; c=relaxed/simple; bh=UMPpd97afvkjw6EqX0kIUAbUS5jqTnijH4v3yoaK9CE=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=omrsN2DAfNsF7c8iT4oO9zdP9qK0Q4tjsXolgpBa2Hhokd3Z8TQJv7XKTjQQo8dUhP6E5QCVI4JwQ2ms4YHVK5DI7AUP+bYrWGSNoiqz8EB0uRH+pQbuvgYqx0MIxDOpg0+9zTNcOpfEn5ZIHJd8QTkek7JucHK8HgvKMtC4+1k= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=q8NbQITT; 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="q8NbQITT" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EFBE3C4CEF7; Thu, 12 Mar 2026 20:27:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1773347234; bh=UMPpd97afvkjw6EqX0kIUAbUS5jqTnijH4v3yoaK9CE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=q8NbQITTcMgHVUNbR38nF+X/4DKeZBAK63O8rcan9BZRUTTxdJfvBC8zjfIGI+99h qsshHV9e7KvmUhSMLCABIS0VvRKMFHgnXdqirRrZi/28On3xbV++zXQ18mNc6JIvYP gGnXwvkDl9NR6uGsisJK0GtIXYFUCpKltj1lrNpg= 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 6.12 240/265] net: ipv6: fix panic when IPv4 route references loopback IPv6 nexthop Date: Thu, 12 Mar 2026 21:10:27 +0100 Message-ID: <20260312201027.004084078@linuxfoundation.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260312201018.128816016@linuxfoundation.org> References: <20260312201018.128816016@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 6.12-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 0f741aa154faf..7b9279d4c363c 100644 --- a/net/ipv6/route.c +++ b/net/ipv6/route.c @@ -3577,7 +3577,6 @@ int fib6_nh_init(struct net *net, struct fib6_nh *fib6_nh, netdevice_tracker *dev_tracker = &fib6_nh->fib_nh_dev_tracker; struct net_device *dev = NULL; struct inet6_dev *idev = NULL; - int addr_type; int err; fib6_nh->fib_nh_family = AF_INET6; @@ -3619,11 +3618,10 @@ 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