ipv6: fix lockdep splat in in6_dump_addrs()

In the Linux kernel, the following vulnerability has been resolved:

ipv6: fix lockdep splat in in6_dump_addrs()

As reported by syzbot, we should not use rcu_dereference()

when rcu_read_lock() is not held.

WARNING: suspicious RCU usage

5.19.0-rc2-syzkaller #0 Not tainted

net/ipv6/addrconf.c:5175 suspicious rcu_dereference_check() usage!

other info that might help us debug this:

rcu_scheduler_active = 2, debug_locks = 1

1 lock held by syz-executor326/3617:

#0: ffffffff8d5848e8 (rtnl_mutex){+.+.}-{3:3}, at: netlink_dump+0xae/0xc20 net/netlink/af_netlink.c:2223

stack backtrace:

CPU: 0 PID: 3617 Comm: syz-executor326 Not tainted 5.19.0-rc2-syzkaller #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011

Call Trace:

<TASK>

__dump_stack lib/dump_stack.c:88 [inline]

dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106

in6_dump_addrs+0x12d1/0x1790 net/ipv6/addrconf.c:5175

inet6_dump_addr+0x9c1/0xb50 net/ipv6/addrconf.c:5300

netlink_dump+0x541/0xc20 net/netlink/af_netlink.c:2275

__netlink_dump_start+0x647/0x900 net/netlink/af_netlink.c:2380

netlink_dump_start include/linux/netlink.h:245 [inline]

rtnetlink_rcv_msg+0x73e/0xc90 net/core/rtnetlink.c:6046

netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2501

netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]

netlink_unicast+0x543/0x7f0 net/netlink/af_netlink.c:1345

netlink_sendmsg+0x917/0xe10 net/netlink/af_netlink.c:1921

sock_sendmsg_nosec net/socket.c:714 [inline]

sock_sendmsg+0xcf/0x120 net/socket.c:734

____sys_sendmsg+0x6eb/0x810 net/socket.c:2492

___sys_sendmsg+0xf3/0x170 net/socket.c:2546

__sys_sendmsg net/socket.c:2575 [inline]

__do_sys_sendmsg net/socket.c:2584 [inline]

__se_sys_sendmsg net/socket.c:2582 [inline]

__x64_sys_sendmsg+0x132/0x220 net/socket.c:2582

do_syscall_x64 arch/x86/entry/common.c:50 [inline]

do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80

entry_SYSCALL_64_after_hwframe+0x46/0xb0