net: ip: fix unexpected return in fib_validate_source()

The errno should be replaced with drop reasons in fib_validate_source(),
and the "-EINVAL" shouldn't be returned. And this causes a warning, which
is reported by syzkaller:

netlink: 'syz-executor371': attribute type 4 has an invalid length.
------------[ cut here ]------------
WARNING: CPU: 0 PID: 5842 at net/core/skbuff.c:1219 __sk_skb_reason_drop net/core/skbuff.c:1216 [inline]
WARNING: CPU: 0 PID: 5842 at net/core/skbuff.c:1219 sk_skb_reason_drop+0x87/0x380 net/core/skbuff.c:1241
Modules linked in:
CPU: 0 UID: 0 PID: 5842 Comm: syz-executor371 Not tainted 6.12.0-rc6-syzkaller-01362-ga58f00ed24b8 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/30/2024
RIP: 0010:__sk_skb_reason_drop net/core/skbuff.c:1216 [inline]
RIP: 0010:sk_skb_reason_drop+0x87/0x380 net/core/skbuff.c:1241
Code: 00 00 00 fc ff df 41 8d 9e 00 00 fc ff bf 01 00 fc ff 89 de e8 ea 9f 08 f8 81 fb 00 00 fc ff 77 3a 4c 89 e5 e8 9a 9b 08 f8 90 <0f> 0b 90 eb 5e bf 01 00 00 00 89 ee e8 c8 9f 08 f8 85 ed 0f 8e 49
RSP: 0018:ffffc90003d57078 EFLAGS: 00010293
RAX: ffffffff898c3ec6 RBX: 00000000fffbffea RCX: ffff8880347a5a00
RDX: 0000000000000000 RSI: 00000000fffbffea RDI: 00000000fffc0001
RBP: dffffc0000000000 R08: ffffffff898c3eb6 R09: 1ffff110023eb7d4
R10: dffffc0000000000 R11: ffffed10023eb7d5 R12: dffffc0000000000
R13: ffff888011f5bdc0 R14: 00000000ffffffea R15: 0000000000000000
FS:  000055557d41e380(0000) GS:ffff8880b8600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000056519d31d608 CR3: 000000007854e000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 kfree_skb_reason include/linux/skbuff.h:1263 [inline]
 ip_rcv_finish_core+0xfde/0x1b50 net/ipv4/ip_input.c:424
 ip_list_rcv_finish net/ipv4/ip_input.c:610 [inline]
 ip_sublist_rcv+0x3b1/0xab0 net/ipv4/ip_input.c:636
 ip_list_rcv+0x42b/0x480 net/ipv4/ip_input.c:670
 __netif_receive_skb_list_ptype net/core/dev.c:5715 [inline]
 __netif_receive_skb_list_core+0x94e/0x980 net/core/dev.c:5762
 __netif_receive_skb_list net/core/dev.c:5814 [inline]
 netif_receive_skb_list_internal+0xa51/0xe30 net/core/dev.c:5905
 netif_receive_skb_list+0x55/0x4b0 net/core/dev.c:5957
 xdp_recv_frames net/bpf/test_run.c:280 [inline]
 xdp_test_run_batch net/bpf/test_run.c:361 [inline]
 bpf_test_run_xdp_live+0x1b5e/0x21b0 net/bpf/test_run.c:390
 bpf_prog_test_run_xdp+0x805/0x11e0 net/bpf/test_run.c:1318
 bpf_prog_test_run+0x2e4/0x360 kernel/bpf/syscall.c:4266
 __sys_bpf+0x48d/0x810 kernel/bpf/syscall.c:5671
 __do_sys_bpf kernel/bpf/syscall.c:5760 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:5758 [inline]
 __x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:5758
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f18af25a8e9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffee4090af8 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f18af25a8e9
RDX: 0000000000000048 RSI: 0000000020000600 RDI: 000000000000000a
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

Fix it by returning "-SKB_DROP_REASON_IP_LOCAL_SOURCE" instead of
"-EINVAL" in fib_validate_source().

Reported-by: syzbot+52fbd90f020788ec7709@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/6738e539.050a0220.e1c64.0002.GAE@google.com/
Fixes: 82d9983ebe ("net: ip: make ip_route_input_noref() return drop reasons")
Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
Acked-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv4/fib_frontend.c

@@ -447,7 +447,7 @@ int fib_validate_source(struct sk_buff *skb, __be32 src, __be32 dst,
 		 * and the same host but different containers are not.
 		 */
 		if (inet_lookup_ifaddr_rcu(net, src))
-			return -EINVAL;
+			return -SKB_DROP_REASON_IP_LOCAL_SOURCE;
 
 ok:
 		*itag = 0;