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Commit 25dd169a authored by Florian Westphal's avatar Florian Westphal Committed by David S. Miller
Browse files

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: 394f51ab ("ipv4: route: set ipv4 RTM_GETROUTE to not use rtnl")
Reported-by: default avatarsyzbot <syzkaller@googlegroups.com>
Signed-off-by: default avatarFlorian Westphal <fw@strlen.de>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent e73b49eb

net/ipv4/fib_semantics.c

+10 −6
Original line number Diff line number Diff line
@@ -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;