net: ipv4: fix route with nexthop object delete warning

FRR folks have hit a kernel warning[1] while deleting routes[2] which is
caused by trying to delete a route pointing to a nexthop id without
specifying nhid but matching on an interface. That is, a route is found
but we hit a warning while matching it. The warning is from
fib_info_nh() in include/net/nexthop.h because we run it on a fib_info
with nexthop object. The call chain is:
 inet_rtm_delroute -> fib_table_delete -> fib_nh_match (called with a
nexthop fib_info and also with fc_oif set thus calling fib_info_nh on
the fib_info and triggering the warning). The fix is to not do any
matching in that branch if the fi has a nexthop object because those are
managed separately. I.e. we should match when deleting without nh spec and
should fail when deleting a nexthop route with old-style nh spec because
nexthop objects are managed separately, e.g.:
 $ ip r show 1.2.3.4/32
 1.2.3.4 nhid 12 via 192.168.11.2 dev dummy0

 $ ip r del 1.2.3.4/32
 $ ip r del 1.2.3.4/32 nhid 12
 <both should work>

 $ ip r del 1.2.3.4/32 dev dummy0
 <should fail with ESRCH>

[1]
 [  523.462226] ------------[ cut here ]------------
 [  523.462230] WARNING: CPU: 14 PID: 22893 at include/net/nexthop.h:468 fib_nh_match+0x210/0x460
 [  523.462236] Modules linked in: dummy rpcsec_gss_krb5 xt_socket nf_socket_ipv4 nf_socket_ipv6 ip6table_raw iptable_raw bpf_preload xt_statistic ip_set ip_vs_sh ip_vs_wrr ip_vs_rr ip_vs xt_mark nf_tables xt_nat veth nf_conntrack_netlink nfnetlink xt_addrtype br_netfilter overlay dm_crypt nfsv3 nfs fscache netfs vhost_net vhost vhost_iotlb tap tun xt_CHECKSUM xt_MASQUERADE xt_conntrack 8021q garp mrp ipt_REJECT nf_reject_ipv4 ip6table_mangle ip6table_nat iptable_mangle iptable_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 iptable_filter bridge stp llc rfcomm snd_seq_dummy snd_hrtimer rpcrdma rdma_cm iw_cm ib_cm ib_core ip6table_filter xt_comment ip6_tables vboxnetadp(OE) vboxnetflt(OE) vboxdrv(OE) qrtr bnep binfmt_misc xfs vfat fat squashfs loop nvidia_drm(POE) nvidia_modeset(POE) nvidia_uvm(POE) nvidia(POE) intel_rapl_msr intel_rapl_common snd_hda_codec_realtek snd_hda_codec_generic ledtrig_audio snd_hda_codec_hdmi btusb btrtl iwlmvm uvcvideo btbcm snd_hda_intel edac_mce_amd
 [  523.462274]  videobuf2_vmalloc videobuf2_memops btintel snd_intel_dspcfg videobuf2_v4l2 snd_intel_sdw_acpi bluetooth snd_usb_audio snd_hda_codec mac80211 snd_usbmidi_lib joydev snd_hda_core videobuf2_common kvm_amd snd_rawmidi snd_hwdep snd_seq videodev ccp snd_seq_device libarc4 ecdh_generic mc snd_pcm kvm iwlwifi snd_timer drm_kms_helper snd cfg80211 cec soundcore irqbypass rapl wmi_bmof i2c_piix4 rfkill k10temp pcspkr acpi_cpufreq nfsd auth_rpcgss nfs_acl lockd grace sunrpc drm zram ip_tables crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmulni_intel nvme sp5100_tco r8169 nvme_core wmi ipmi_devintf ipmi_msghandler fuse
 [  523.462300] CPU: 14 PID: 22893 Comm: ip Tainted: P           OE     5.16.18-200.fc35.x86_64 #1
 [  523.462302] Hardware name: Micro-Star International Co., Ltd. MS-7C37/MPG X570 GAMING EDGE WIFI (MS-7C37), BIOS 1.C0 10/29/2020
 [  523.462303] RIP: 0010:fib_nh_match+0x210/0x460
 [  523.462304] Code: 7c 24 20 48 8b b5 90 00 00 00 e8 bb ee f4 ff 48 8b 7c 24 20 41 89 c4 e8 ee eb f4 ff 45 85 e4 0f 85 2e fe ff ff e9 4c ff ff ff <0f> 0b e9 17 ff ff ff 3c 0a 0f 85 61 fe ff ff 48 8b b5 98 00 00 00
 [  523.462306] RSP: 0018:ffffaa53d4d87928 EFLAGS: 00010286
 [  523.462307] RAX: 0000000000000000 RBX: ffffaa53d4d87a90 RCX: ffffaa53d4d87bb0
 [  523.462308] RDX: ffff9e3d2ee6be80 RSI: ffffaa53d4d87a90 RDI: ffffffff920ed380
 [  523.462309] RBP: ffff9e3d2ee6be80 R08: 0000000000000064 R09: 0000000000000000
 [  523.462310] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000031
 [  523.462310] R13: 0000000000000020 R14: 0000000000000000 R15: ffff9e3d331054e0
 [  523.462311] FS:  00007f245517c1c0(0000) GS:ffff9e492ed80000(0000) knlGS:0000000000000000
 [  523.462313] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 [  523.462313] CR2: 000055e5dfdd8268 CR3: 00000003ef488000 CR4: 0000000000350ee0
 [  523.462315] Call Trace:
 [  523.462316]  <TASK>
 [  523.462320]  fib_table_delete+0x1a9/0x310
 [  523.462323]  inet_rtm_delroute+0x93/0x110
 [  523.462325]  rtnetlink_rcv_msg+0x133/0x370
 [  523.462327]  ? _copy_to_iter+0xb5/0x6f0
 [  523.462330]  ? rtnl_calcit.isra.0+0x110/0x110
 [  523.462331]  netlink_rcv_skb+0x50/0xf0
 [  523.462334]  netlink_unicast+0x211/0x330
 [  523.462336]  netlink_sendmsg+0x23f/0x480
 [  523.462338]  sock_sendmsg+0x5e/0x60
 [  523.462340]  ____sys_sendmsg+0x22c/0x270
 [  523.462341]  ? import_iovec+0x17/0x20
 [  523.462343]  ? sendmsg_copy_msghdr+0x59/0x90
 [  523.462344]  ? __mod_lruvec_page_state+0x85/0x110
 [  523.462348]  ___sys_sendmsg+0x81/0xc0
 [  523.462350]  ? netlink_seq_start+0x70/0x70
 [  523.462352]  ? __dentry_kill+0x13a/0x180
 [  523.462354]  ? __fput+0xff/0x250
 [  523.462356]  __sys_sendmsg+0x49/0x80
 [  523.462358]  do_syscall_64+0x3b/0x90
 [  523.462361]  entry_SYSCALL_64_after_hwframe+0x44/0xae
 [  523.462364] RIP: 0033:0x7f24552aa337
 [  523.462365] Code: 0e 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b9 0f 1f 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 b8 2e 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 51 c3 48 83 ec 28 89 54 24 1c 48 89 74 24 10
 [  523.462366] RSP: 002b:00007fff7f05a838 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
 [  523.462368] RAX: ffffffffffffffda RBX: 000000006245bf91 RCX: 00007f24552aa337
 [  523.462368] RDX: 0000000000000000 RSI: 00007fff7f05a8a0 RDI: 0000000000000003
 [  523.462369] RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000
 [  523.462370] R10: 0000000000000008 R11: 0000000000000246 R12: 0000000000000001
 [  523.462370] R13: 00007fff7f05ce08 R14: 0000000000000000 R15: 000055e5dfdd1040
 [  523.462373]  </TASK>
 [  523.462374] ---[ end trace ba537bc16f6bf4ed ]---

[2] https://github.com/FRRouting/frr/issues/6412

Fixes: 4c7e8084 ("ipv4: Plumb support for nexthop object in a fib_info")
Signed-off-by: Nikolay Aleksandrov <razor@blackwall.org>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/fib_semantics.c

@@ -889,8 +889,13 @@ int fib_nh_match(struct net *net, struct fib_config *cfg, struct fib_info *fi,
 	}
 
 	if (cfg->fc_oif || cfg->fc_gw_family) {
-		struct fib_nh *nh = fib_info_nh(fi, 0);
+		struct fib_nh *nh;
+
+		/* cannot match on nexthop object attributes */
+		if (fi->nh)
+			return 1;
 
+		nh = fib_info_nh(fi, 0);
 		if (cfg->fc_encap) {
 			if (fib_encap_match(net, cfg->fc_encap_type,
 					    cfg->fc_encap, nh, cfg, extack))