fib: fib_dump_info can no longer use __in_dev_get_rtnl

syzbot reported yet another regression added with DOIT_UNLOCKED.
When nexthop is marked as dead, fib_dump_info uses __in_dev_get_rtnl():

./include/linux/inetdevice.h:230 suspicious rcu_dereference_protected() usage!
rcu_scheduler_active = 2, debug_locks = 1
1 lock held by syz-executor2/23859:
 #0:  (rcu_read_lock){....}, at: [<ffffffff840283f0>]
inet_rtm_getroute+0xaa0/0x2d70 net/ipv4/route.c:2738
[..]
  lockdep_rcu_suspicious+0x123/0x170 kernel/locking/lockdep.c:4665
  __in_dev_get_rtnl include/linux/inetdevice.h:230 [inline]
  fib_dump_info+0x1136/0x13d0 net/ipv4/fib_semantics.c:1377
  inet_rtm_getroute+0xf97/0x2d70 net/ipv4/route.c:2785
..

This isn't safe anymore, callers either hold RTNL mutex or rcu read lock,
so these spots must use rcu_dereference_rtnl() or plain rcu_derefence()
(plus unconditional rcu read lock).

This does the latter.

Fixes: 394f51abb3d04f ("ipv4: route: set ipv4 RTM_GETROUTE to not use rtnl")
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index 57a5d48acee84b27de00d49640220ae8e5167389..01ed22139ac2b113952dce2c11916ce2439719d6 100644 (file)
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -1365,8 +1365,6 @@ int fib_dump_info(struct sk_buff *skb, u32 portid, u32 seq, int event,
            nla_put_in_addr(skb, RTA_PREFSRC, fi->fib_prefsrc))
                goto nla_put_failure;
        if (fi->fib_nhs == 1) {
-               struct in_device *in_dev;
-
                if (fi->fib_nh->nh_gw &&
                    nla_put_in_addr(skb, RTA_GATEWAY, fi->fib_nh->nh_gw))
                        goto nla_put_failure;
@@ -1374,10 +1372,14 @@ int fib_dump_info(struct sk_buff *skb, u32 portid, u32 seq, int event,
                    nla_put_u32(skb, RTA_OIF, fi->fib_nh->nh_oif))
                        goto nla_put_failure;
                if (fi->fib_nh->nh_flags & RTNH_F_LINKDOWN) {
-                       in_dev = __in_dev_get_rtnl(fi->fib_nh->nh_dev);
+                       struct in_device *in_dev;
+
+                       rcu_read_lock();
+                       in_dev = __in_dev_get_rcu(fi->fib_nh->nh_dev);
                        if (in_dev &&
                            IN_DEV_IGNORE_ROUTES_WITH_LINKDOWN(in_dev))
                                rtm->rtm_flags |= RTNH_F_DEAD;
+                       rcu_read_unlock();
                }
                if (fi->fib_nh->nh_flags & RTNH_F_OFFLOAD)
                        rtm->rtm_flags |= RTNH_F_OFFLOAD;
@@ -1400,18 +1402,20 @@ int fib_dump_info(struct sk_buff *skb, u32 portid, u32 seq, int event,
                        goto nla_put_failure;
 
                for_nexthops(fi) {
-                       struct in_device *in_dev;
-
                        rtnh = nla_reserve_nohdr(skb, sizeof(*rtnh));
                        if (!rtnh)
                                goto nla_put_failure;
 
                        rtnh->rtnh_flags = nh->nh_flags & 0xFF;
                        if (nh->nh_flags & RTNH_F_LINKDOWN) {
-                               in_dev = __in_dev_get_rtnl(nh->nh_dev);
+                               struct in_device *in_dev;
+
+                               rcu_read_lock();
+                               in_dev = __in_dev_get_rcu(nh->nh_dev);
                                if (in_dev &&
                                    IN_DEV_IGNORE_ROUTES_WITH_LINKDOWN(in_dev))
                                        rtnh->rtnh_flags |= RTNH_F_DEAD;
+                               rcu_read_unlock();
                        }
                        rtnh->rtnh_hops = nh->nh_weight - 1;
                        rtnh->rtnh_ifindex = nh->nh_oif;