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 4B54D1F152D; Tue, 30 Sep 2025 15:04:27 +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=1759244667; cv=none; b=I9cuA7Qf2guplrjL+OEmxQUE1GB4Gqqebfdr4eQsIW4WjAXey6HIrrCssMNGw23klRbSpxPA8fmMyhL411nyYPzUCdPaVQRlwB2jwtYfkU9ucsrCzsHGDcV3elTDQbis2ov/S1V459RQp//Uv7iFd6P4mFOjK/xVwYnyXMzNzMs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759244667; c=relaxed/simple; bh=ZWyy0SxSaOPgW0G9mK1qAFIDoyTXHwF7raUGF6K2Rl8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=FburXO8M8DU5t6SQu9UrRm2KL/DuAOrTbAYw2iUL5DE23LhQMppLtrPWRPDYgGumwUIRGyvByLfJ2xg9TMwurCtTC81biSRr5Nt9BC4T6JdJlWTLiU2oj9zHBNd0PZooq/6ufvn43m8iZKpdx09anROGO7L70mKczFUhc9li8R0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=OmyQ1OYK; 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="OmyQ1OYK" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 76DF0C4CEF0; Tue, 30 Sep 2025 15:04:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1759244666; bh=ZWyy0SxSaOPgW0G9mK1qAFIDoyTXHwF7raUGF6K2Rl8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=OmyQ1OYKsVnOPMjB7RhG9E6SxrYjbuGKwaAK+XAbxcqZjCqxONtcWhlTVgrODbygv kWovBKZnntwAY1ZHQmqBW+wr8/gNFO31Tz+ydRN57DTdmXLIn2CIDPc0u723q81eNg ADRKc8mSSS6MAI2p6jLDhTSdHgK/AFJEZ1dcQmCg= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, syzbot+6596516dd2b635ba2350@syzkaller.appspotmail.com, Ido Schimmel , David Ahern , Jakub Kicinski , Sasha Levin Subject: [PATCH 6.16 077/143] nexthop: Forbid FDB status change while nexthop is in a group Date: Tue, 30 Sep 2025 16:46:41 +0200 Message-ID: <20250930143834.309043923@linuxfoundation.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20250930143831.236060637@linuxfoundation.org> References: <20250930143831.236060637@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 6.16-stable review patch. If anyone has any objections, please let me know. ------------------ From: Ido Schimmel [ Upstream commit 390b3a300d7872cef9588f003b204398be69ce08 ] The kernel forbids the creation of non-FDB nexthop groups with FDB nexthops: # ip nexthop add id 1 via 192.0.2.1 fdb # ip nexthop add id 2 group 1 Error: Non FDB nexthop group cannot have fdb nexthops. And vice versa: # ip nexthop add id 3 via 192.0.2.2 dev dummy1 # ip nexthop add id 4 group 3 fdb Error: FDB nexthop group can only have fdb nexthops. However, as long as no routes are pointing to a non-FDB nexthop group, the kernel allows changing the type of a nexthop from FDB to non-FDB and vice versa: # ip nexthop add id 5 via 192.0.2.2 dev dummy1 # ip nexthop add id 6 group 5 # ip nexthop replace id 5 via 192.0.2.2 fdb # echo $? 0 This configuration is invalid and can result in a NPD [1] since FDB nexthops are not associated with a nexthop device: # ip route add 198.51.100.1/32 nhid 6 # ping 198.51.100.1 Fix by preventing nexthop FDB status change while the nexthop is in a group: # ip nexthop add id 7 via 192.0.2.2 dev dummy1 # ip nexthop add id 8 group 7 # ip nexthop replace id 7 via 192.0.2.2 fdb Error: Cannot change nexthop FDB status while in a group. [1] BUG: kernel NULL pointer dereference, address: 00000000000003c0 [...] Oops: Oops: 0000 [#1] SMP CPU: 6 UID: 0 PID: 367 Comm: ping Not tainted 6.17.0-rc6-virtme-gb65678cacc03 #1 PREEMPT(voluntary) Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-4.fc41 04/01/2014 RIP: 0010:fib_lookup_good_nhc+0x1e/0x80 [...] Call Trace: fib_table_lookup+0x541/0x650 ip_route_output_key_hash_rcu+0x2ea/0x970 ip_route_output_key_hash+0x55/0x80 __ip4_datagram_connect+0x250/0x330 udp_connect+0x2b/0x60 __sys_connect+0x9c/0xd0 __x64_sys_connect+0x18/0x20 do_syscall_64+0xa4/0x2a0 entry_SYSCALL_64_after_hwframe+0x4b/0x53 Fixes: 38428d68719c ("nexthop: support for fdb ecmp nexthops") Reported-by: syzbot+6596516dd2b635ba2350@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/68c9a4d2.050a0220.3c6139.0e63.GAE@google.com/ Tested-by: syzbot+6596516dd2b635ba2350@syzkaller.appspotmail.com Signed-off-by: Ido Schimmel Reviewed-by: David Ahern Link: https://patch.msgid.link/20250921150824.149157-2-idosch@nvidia.com Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- net/ipv4/nexthop.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/net/ipv4/nexthop.c b/net/ipv4/nexthop.c index 4397e89d3123a..423f876d14c6a 100644 --- a/net/ipv4/nexthop.c +++ b/net/ipv4/nexthop.c @@ -2400,6 +2400,13 @@ static int replace_nexthop_single(struct net *net, struct nexthop *old, return -EINVAL; } + if (!list_empty(&old->grp_list) && + rtnl_dereference(new->nh_info)->fdb_nh != + rtnl_dereference(old->nh_info)->fdb_nh) { + NL_SET_ERR_MSG(extack, "Cannot change nexthop FDB status while in a group"); + return -EINVAL; + } + err = call_nexthop_notifiers(net, NEXTHOP_EVENT_REPLACE, new, extack); if (err) return err; -- 2.51.0