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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: 394f51abb3 ("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>
This commit is contained in:
Florian Westphal 2017-11-02 16:02:20 +01:00 committed by David S. Miller
parent e73b49ebd9
commit 25dd169aea
1 changed files with 10 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

16
net/ipv4/fib_semantics.c
View File

@ -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;