From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-172.mta0.migadu.com (out-172.mta0.migadu.com [91.218.175.172]) (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 113783191D8 for ; Mon, 13 Apr 2026 11:45:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776080748; cv=none; b=cKZCuGJzZM4SIzWnnjfwQGxaUUOnGz5D6k/ModDUNmM6FQJE4+6yS0ZfvBMuh5lMHuEVa+RT4lOejlYxDhco5omtB+4JfjCR0X58yDTPTrjLolNiVCZAubUj26XJEWOnAYWMP84CxTsAYg7FYHvdAntHPacOzgTowLlymWF7sYw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776080748; c=relaxed/simple; bh=qCctWpwE/nJLf++5g3G/9Uwl9i4qFereP2gXRPnUqE0=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=mk6KWSUcdU5ugv01K8E4k4Jr871+yZE8cHlz1LFpOiQL4ZcCUa4GuWBl/f3PK90PU8hw9RsD8UEtd6YasAOAvFAHFmpJ65oTxOQfbLq2UJG40C7Owgq+ZHncx4704VKOmcWt2M4aVP5q8V9m8SHCe8Tn+mJQQc1K+8aUDU0+gbU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=tar9Mtf2; arc=none smtp.client-ip=91.218.175.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="tar9Mtf2" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1776080734; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=w6n8HirOrz8fD1oV0V8xDHH8OC6CP4l/Of8LvNQ4UZ4=; b=tar9Mtf2ozzNpqrMqCoWbAFCpRDH6SUCJj5d4CAh+vKTMfM6iGOC92ph4p2Gj9U22tfJpk yMHwEARH8Bs+hFhp3OrKTx7vgw2mT+2Aal+hjL/YN80rMrwsXkX7B+vHf5ZSOhOt5hrwyR jy22WdaWn21eATchOQkDEj+/PeBELjs= From: Jiayuan Chen To: netdev@vger.kernel.org Cc: Jiayuan Chen , David Ahern , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Shuah Khan , linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [PATCH net v1 1/2] nexthop: fix IPv6 route referencing IPv4 nexthop Date: Mon, 13 Apr 2026 19:45:19 +0800 Message-ID: <20260413114522.147784-1-jiayuan.chen@linux.dev> Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT syzbot reported a panic [1] [2]. When an IPv6 nexthop is replaced with an IPv4 nexthop, the has_v4 flag of all groups containing this nexthop is not updated. This is because nh_group_v4_update is only called when replacing AF_INET to AF_INET6, but the reverse direction (AF_INET6 to AF_INET) is missed. This allows a stale has_v4=false to bypass fib6_check_nexthop, causing IPv6 routes to be attached to groups that effectively contain only AF_INET members. Subsequent route lookups then call nexthop_fib6_nh() which returns NULL for the AF_INET member, leading to a NULL pointer dereference. Fix by calling nh_group_v4_update whenever the family changes, not just AF_INET to AF_INET6. Reproducer: # AF_INET6 blackhole ip -6 nexthop add id 1 blackhole # group with has_v4=false ip nexthop add id 100 group 1 # replace with AF_INET (no -6), has_v4 stays false ip nexthop replace id 1 blackhole # pass stale has_v4 check ip -6 route add 2001:db8::/64 nhid 100 # panic ping -6 2001:db8::1 [1] https://syzkaller.appspot.com/bug?id=e17283eb2f8dcf3dd9b47fe6f67a95f71faadad0 [2] https://syzkaller.appspot.com/bug?id=8699b6ae54c9f35837d925686208402949e12ef3 Fixes: 7bf4796dd099 ("nexthops: add support for replace") Signed-off-by: Jiayuan Chen --- net/ipv4/nexthop.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/net/ipv4/nexthop.c b/net/ipv4/nexthop.c index 2c9036c719b6..11a763cbc848 100644 --- a/net/ipv4/nexthop.c +++ b/net/ipv4/nexthop.c @@ -2466,10 +2466,10 @@ static int replace_nexthop_single(struct net *net, struct nexthop *old, goto err_notify; } - /* When replacing an IPv4 nexthop with an IPv6 nexthop, potentially + /* When replacing a nexthop with one of a different family, potentially * update IPv4 indication in all the groups using the nexthop. */ - if (oldi->family == AF_INET && newi->family == AF_INET6) { + if (oldi->family != newi->family) { list_for_each_entry(nhge, &old->grp_list, nh_list) { struct nexthop *nhp = nhge->nh_parent; struct nh_group *nhg; -- 2.43.0