netdevsim: fix nsim_fib6_rt_create() error path

It seems nsim_fib6_rt_create() intent was to return
either a valid pointer or an embedded error code.

BUG: unable to handle page fault for address: fffffffffffffff4
PGD 9870067 P4D 9870067 PUD 9872067 PMD 0
Oops: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 22851 Comm: syz-executor.1 Not tainted 5.5.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:jhash2 include/linux/jhash.h:125 [inline]
RIP: 0010:rhashtable_jhash2+0x76/0x2c0 lib/rhashtable.c:963
Code: b9 00 00 00 00 00 fc ff df 48 c1 e8 03 0f b6 14 08 4c 89 f0 83 e0 07 83 c0 03 38 d0 7c 08 84 d2 0f 85 30 02 00 00 49 8d 7e 04 <41> 8b 06 48 be 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 0f b6
RSP: 0018:ffffc90016127190 EFLAGS: 00010246
RAX: 0000000000000007 RBX: 00000000dfb3ab49 RCX: dffffc0000000000
RDX: 0000000000000000 RSI: ffffffff839ba7c8 RDI: fffffffffffffff8
RBP: ffffc900161271c0 R08: ffff8880951f8640 R09: ffffed1015d0703d
R10: ffffed1015d0703c R11: ffff8880ae8381e3 R12: 00000000dfb3ab49
R13: 00000000dfb3ab49 R14: fffffffffffffff4 R15: 0000000000000007
FS:  00007f40bfbc6700(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: fffffffffffffff4 CR3: 0000000093660000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 rht_key_get_hash include/linux/rhashtable.h:133 [inline]
 rht_key_hashfn include/linux/rhashtable.h:159 [inline]
 rht_head_hashfn include/linux/rhashtable.h:174 [inline]
 __rhashtable_insert_fast.constprop.0+0xe15/0x1180 include/linux/rhashtable.h:723
 rhashtable_insert_fast include/linux/rhashtable.h:832 [inline]
 nsim_fib6_rt_add drivers/net/netdevsim/fib.c:603 [inline]
 nsim_fib6_rt_insert drivers/net/netdevsim/fib.c:658 [inline]
 nsim_fib6_event drivers/net/netdevsim/fib.c:719 [inline]
 nsim_fib_event drivers/net/netdevsim/fib.c:744 [inline]
 nsim_fib_event_nb+0x1b16/0x2600 drivers/net/netdevsim/fib.c:772
 notifier_call_chain+0xc2/0x230 kernel/notifier.c:83
 __atomic_notifier_call_chain+0xa6/0x1a0 kernel/notifier.c:173
 atomic_notifier_call_chain+0x2e/0x40 kernel/notifier.c:183
 call_fib_notifiers+0x173/0x2a0 net/core/fib_notifier.c:35
 call_fib6_notifiers+0x4b/0x60 net/ipv6/fib6_notifier.c:22
 call_fib6_entry_notifiers+0xfb/0x150 net/ipv6/ip6_fib.c:399
 fib6_add_rt2node net/ipv6/ip6_fib.c:1216 [inline]
 fib6_add+0x20cd/0x3ec0 net/ipv6/ip6_fib.c:1471
 __ip6_ins_rt+0x54/0x80 net/ipv6/route.c:1315
 ip6_ins_rt+0x96/0xd0 net/ipv6/route.c:1325
 __ipv6_dev_ac_inc+0x76f/0xb20 net/ipv6/anycast.c:324
 ipv6_sock_ac_join+0x4c1/0x790 net/ipv6/anycast.c:139
 do_ipv6_setsockopt.isra.0+0x3908/0x4290 net/ipv6/ipv6_sockglue.c:670
 ipv6_setsockopt+0xff/0x180 net/ipv6/ipv6_sockglue.c:944
 udpv6_setsockopt+0x68/0xb0 net/ipv6/udp.c:1564
 sock_common_setsockopt+0x94/0xd0 net/core/sock.c:3149
 __sys_setsockopt+0x261/0x4c0 net/socket.c:2130
 __do_sys_setsockopt net/socket.c:2146 [inline]
 __se_sys_setsockopt net/socket.c:2143 [inline]
 __x64_sys_setsockopt+0xbe/0x150 net/socket.c:2143
 do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45aff9

Fixes: 48bb9eb4 ("netdevsim: fib: Add dummy implementation for FIB offload")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Cc: Ido Schimmel <idosch@mellanox.com>
Reviewed-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/netdevsim/fib.c

@@ -467,7 +467,7 @@ nsim_fib6_rt_create(struct nsim_fib_data *data,
 
 	fib6_rt = kzalloc(sizeof(*fib6_rt), GFP_ATOMIC);
 	if (!fib6_rt)
-		return NULL;
+		return ERR_PTR(-ENOMEM);
 
 	nsim_fib_rt_init(data, &fib6_rt->common, &rt->fib6_dst.addr,
 			 sizeof(rt->fib6_dst.addr), rt->fib6_dst.plen, AF_INET6,
@@ -650,8 +650,8 @@ static int nsim_fib6_rt_insert(struct nsim_fib_data *data,
 	int err;
 
 	fib6_rt = nsim_fib6_rt_create(data, fen6_info);
-	if (!fib6_rt)
-		return -ENOMEM;
+	if (IS_ERR(fib6_rt))
+		return PTR_ERR(fib6_rt);
 
 	fib6_rt_old = nsim_fib6_rt_lookup(&data->fib_rt_ht, fen6_info->rt);
 	if (!fib6_rt_old)