ipmr: properly check rhltable_init() return value

commit 8fb472c09b9d ("ipmr: improve hash scalability")
added a call to rhltable_init() without checking its return value.

This problem was then later copied to IPv6 and factorized in commit
0bbbf0e7d0e7 ("ipmr, ip6mr: Unite creation of new mr_table")

kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 1 PID: 31552 Comm: syz-executor7 Not tainted 4.17.0-rc5+ #60
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:rht_key_hashfn include/linux/rhashtable.h:277 [inline]
RIP: 0010:__rhashtable_lookup include/linux/rhashtable.h:630 [inline]
RIP: 0010:rhltable_lookup include/linux/rhashtable.h:716 [inline]
RIP: 0010:mr_mfc_find_parent+0x2ad/0xbb0 net/ipv4/ipmr_base.c:63
RSP: 0018:ffff8801826aef70 EFLAGS: 00010203
RAX: 0000000000000001 RBX: 0000000000000001 RCX: ffffc90001ea0000
RDX: 0000000000000079 RSI: ffffffff8661e859 RDI: 000000000000000c
RBP: ffff8801826af1c0 R08: ffff8801b2212000 R09: ffffed003b5e46c2
R10: ffffed003b5e46c2 R11: ffff8801daf23613 R12: dffffc0000000000
R13: ffff8801826af198 R14: ffff8801cf8225c0 R15: ffff8801826af658
FS:  00007ff7fa732700(0000) GS:ffff8801daf00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000003ffffff9c CR3: 00000001b0210000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 ip6mr_cache_find_parent net/ipv6/ip6mr.c:981 [inline]
 ip6mr_mfc_delete+0x1fe/0x6b0 net/ipv6/ip6mr.c:1221
 ip6_mroute_setsockopt+0x15c6/0x1d70 net/ipv6/ip6mr.c:1698
 do_ipv6_setsockopt.isra.9+0x422/0x4660 net/ipv6/ipv6_sockglue.c:163
 ipv6_setsockopt+0xbd/0x170 net/ipv6/ipv6_sockglue.c:922
 rawv6_setsockopt+0x59/0x140 net/ipv6/raw.c:1060
 sock_common_setsockopt+0x9a/0xe0 net/core/sock.c:3039
 __sys_setsockopt+0x1bd/0x390 net/socket.c:1903
 __do_sys_setsockopt net/socket.c:1914 [inline]
 __se_sys_setsockopt net/socket.c:1911 [inline]
 __x64_sys_setsockopt+0xbe/0x150 net/socket.c:1911
 do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Fixes: 8fb472c09b9d ("ipmr: improve hash scalability")
Fixes: 0bbbf0e7d0e7 ("ipmr, ip6mr: Unite creation of new mr_table")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Cc: Yuval Mintz <yuvalm@mellanox.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Acked-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/ipmr_base.c

@@ -43,7 +43,10 @@ mr_table_alloc(struct net *net, u32 id,
 	write_pnet(&mrt->net, net);
 
 	mrt->ops = *ops;
-	rhltable_init(&mrt->mfc_hash, mrt->ops.rht_params);
+	if (rhltable_init(&mrt->mfc_hash, mrt->ops.rht_params)) {
+		kfree(mrt);
+		return NULL;
+	}
 	INIT_LIST_HEAD(&mrt->mfc_cache_list);
 	INIT_LIST_HEAD(&mrt->mfc_unres_queue);