ipv6: Fix idev->addr_list corruption

addrconf_ifdown() removes elements from the idev->addr_list without
holding the idev->lock.

If this happens while the loop in __ipv6_dev_get_saddr() is handling the
same element, that function ends up in an infinite loop:

  NMI watchdog: BUG: soft lockup - CPU#1 stuck for 23s! [test:1719]
  Call Trace:
   ipv6_get_saddr_eval+0x13c/0x3a0
   __ipv6_dev_get_saddr+0xe4/0x1f0
   ipv6_dev_get_saddr+0x1b4/0x204
   ip6_dst_lookup_tail+0xcc/0x27c
   ip6_dst_lookup_flow+0x38/0x80
   udpv6_sendmsg+0x708/0xba8
   sock_sendmsg+0x18/0x30
   SyS_sendto+0xb8/0xf8
   syscall_common+0x34/0x58

Fixes: 6a923934c33 (Revert "ipv6: Revert optional address flusing on ifdown.")
Signed-off-by: Rabin Vincent <rabinv@axis.com>
Acked-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 7 insertions, 4 deletions

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 363172527e43..80ce478c4851 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -3626,14 +3626,19 @@ restart:
         INIT_LIST_HEAD(&del_list);
         list_for_each_entry_safe(ifa, tmp, &idev->addr_list, if_list) {
                 struct rt6_info *rt = NULL;
+                bool keep;
 
                 addrconf_del_dad_work(ifa);
 
+                keep = keep_addr && (ifa->flags & IFA_F_PERMANENT) &&
+                        !addr_is_local(&ifa->addr);
+                if (!keep)
+                        list_move(&ifa->if_list, &del_list);
+
                 write_unlock_bh(&idev->lock);
                 spin_lock_bh(&ifa->lock);
 
-                if (keep_addr && (ifa->flags & IFA_F_PERMANENT) &&
-                    !addr_is_local(&ifa->addr)) {
+                if (keep) {
                         /* set state to skip the notifier below */
                         state = INET6_IFADDR_STATE_DEAD;
                         ifa->state = 0;
@@ -3645,8 +3650,6 @@ restart:
                 } else {
                         state = ifa->state;
                         ifa->state = INET6_IFADDR_STATE_DEAD;
-
-                        list_move(&ifa->if_list, &del_list);
                 }
 
                 spin_unlock_bh(&ifa->lock);