[PATCH v1 net] ipv6: Fix null-ptr-deref in addrconf_add_ifaddr().

[Kuniyuki Iwashima <kuniyu@amazon.com>]

The cited commit placed netdev_lock_ops() just after __dev_get_by_index()
in addrconf_add_ifaddr(), where dev could be NULL as reported. [0]

Let's call netdev_lock_ops() only when dev is not NULL.

[0]:
Oops: general protection fault, probably for non-canonical address 0xdffffc0000000198: 0000 [#1] SMP KASAN NOPTI
KASAN: null-ptr-deref in range [0x0000000000000cc0-0x0000000000000cc7]
CPU: 3 UID: 0 PID: 12032 Comm: syz.0.15 Not tainted 6.14.0-13408-g9f867ba24d36 #1 PREEMPT(full)
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
RIP: 0010:addrconf_add_ifaddr (./include/net/netdev_lock.h:30 ./include/net/netdev_lock.h:41 net/ipv6/addrconf.c:3157)
Code: 8b b4 24 94 00 00 00 4c 89 ef e8 7e 4c 2f ff 4c 8d b0 c5 0c 00 00 48 89 c3 48 b8 00 00 00 00 00 fc ff df 4c 89 f2 48 c1 ea 03 <0f> b6 04 02 4c 89 f2 83 e2 07 38 d0 7f 08 80
RSP: 0018:ffffc90015b0faa0 EFLAGS: 00010213
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000198 RSI: ffffffff893162f2 RDI: ffff888078cb0338
RBP: ffffc90015b0fbb0 R08: 0000000000000000 R09: fffffbfff20cbbe2
R10: ffffc90015b0faa0 R11: 0000000000000000 R12: 1ffff92002b61f54
R13: ffff888078cb0000 R14: 0000000000000cc5 R15: ffff888078cb0000
FS: 00007f92559ed640(0000) GS:ffff8882a8659000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f92559ecfc8 CR3: 000000001c39e000 CR4: 00000000000006f0
Call Trace:
 <TASK>
 inet6_ioctl (net/ipv6/af_inet6.c:580)
 sock_do_ioctl (net/socket.c:1196)
 sock_ioctl (net/socket.c:1314)
 __x64_sys_ioctl (fs/ioctl.c:52 fs/ioctl.c:906 fs/ioctl.c:892 fs/ioctl.c:892)
 do_syscall_64 (arch/x86/entry/syscall_64.c:63 arch/x86/entry/syscall_64.c:94)
 entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130
RIP: 0033:0x7f9254b9c62d
Code: 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 f3 0f 1e fa 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 a8 ff f8
RSP: 002b:00007f92559ecf98 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f9254d65f80 RCX: 00007f9254b9c62d
RDX: 0000000020000040 RSI: 0000000000008916 RDI: 0000000000000003
RBP: 00007f9254c264d3 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f9254d65f80 R15: 00007f92559cd000
 </TASK>
Modules linked in:

Fixes: 8965c160b8f7 ("net: use netif_disable_lro in ipv6_add_dev")
Reported-by: syzkaller <syzkaller@googlegroups.com>
Reported-by: Hui Guo <guohui.study@gmail.com>
Closes: https://lore.kernel.org/netdev/CAHOo4gK+tdU1B14Kh6tg-tNPqnQ1qGLfinONFVC43vmgEPnXXw@mail.gmail.com/
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
---
 net/ipv6/addrconf.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index c3b908fccbc1..9c52ed23ff23 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -3154,12 +3154,13 @@ int addrconf_add_ifaddr(struct net *net, void __user *arg)
 
 	rtnl_net_lock(net);
 	dev = __dev_get_by_index(net, ireq.ifr6_ifindex);
-	netdev_lock_ops(dev);
-	if (dev)
+	if (dev) {
+		netdev_lock_ops(dev);
 		err = inet6_addr_add(net, dev, &cfg, 0, 0, NULL);
-	else
+		netdev_unlock_ops(dev);
+	} else {
 		err = -ENODEV;
-	netdev_unlock_ops(dev);
+	}
 	rtnl_net_unlock(net);
 	return err;
 }
-- 
2.48.1