From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 D6E0036D9EA; Wed, 20 May 2026 17:43:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779299029; cv=none; b=MocO0D1xsfL94gRZXgWQp86z4FUTJqm0anvA0c5wis20WPZKy0WujFR/LCaTU/RHlKz814Y2jGPPpTeEjc8AvOcMXy4Kfrsm5dwwTTF/BDJUYeyg41jAQ3vtmSg76YQjINew0NF9a1UtvECKtU7ZnE2MN66S/i7IBzkuL3rorrI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779299029; c=relaxed/simple; bh=HV9v6UyCNHB4+KIqTVz/K3m8gOg5SiTmImNTxFhSchs=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=RXlfbVOrzLxTWxPuI0861BbP0ja/IcA9/TdkbnONNICba4lHFA/b3OdaYjw6d5/gzP+As5Ws6HODIPY6dhmfSvbaTqFrqwUAs+mtw3T3FoacU1bdyO38d6hlfDIth9DXi2kGvtaSWGKv8CkDjkVsV6pPOKY9uDy+2B1fx0BQDPg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Lq/h4gqM; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="Lq/h4gqM" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 481AE1F000E9; Wed, 20 May 2026 17:43:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1779299027; bh=74yri5UrAz7uGZagnjKlIC4R0kyjQ9CpW4EThBOfUKg=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=Lq/h4gqMziQGQsuYCWSiZpUciKyF63Znd0v/HCtBE+nMiq3dyVdAxwHcja+cnGnEj TJCTbC78EhbLNFKobUZBHLs4ofLczgrNUqx1edT1L4QOlgVCPw+ClY/WL+MRSM2UNN lUnmyIZL8qkJRFp29fuU0jbDgKSe40Ep7kquWuWA= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Jiayuan Chen , David Ahern , Paolo Abeni , Sasha Levin Subject: [PATCH 6.18 618/957] nexthop: fix IPv6 route referencing IPv4 nexthop Date: Wed, 20 May 2026 18:18:21 +0200 Message-ID: <20260520162147.936760269@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260520162134.554764788@linuxfoundation.org> References: <20260520162134.554764788@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jiayuan Chen [ Upstream commit 29c95185ba32b621fbc3800fb86e7dc3edf5c2be ] 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 Reviewed-by: David Ahern Link: https://patch.msgid.link/20260413114522.147784-1-jiayuan.chen@linux.dev Signed-off-by: Paolo Abeni Signed-off-by: Sasha Levin --- 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 c958b8edfe540..5a95b64b61c59 100644 --- a/net/ipv4/nexthop.c +++ b/net/ipv4/nexthop.c @@ -2469,10 +2469,10 @@ 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; -- 2.53.0