[PATCH net-next 1/2] net/ipv6: add rcu locking to ip6_negative_advice

[David Ahern]

syzbot reported a suspicious rcu_dereference_check:
  __dump_stack lib/dump_stack.c:77 [inline]
  dump_stack+0x1b9/0x294 lib/dump_stack.c:113
  lockdep_rcu_suspicious+0x14a/0x153 kernel/locking/lockdep.c:4592
  rt6_check_expired+0x38b/0x3e0 net/ipv6/route.c:410
  ip6_negative_advice+0x67/0xc0 net/ipv6/route.c:2204
  dst_negative_advice include/net/sock.h:1786 [inline]
  sock_setsockopt+0x138f/0x1fe0 net/core/sock.c:1051
  __sys_setsockopt+0x2df/0x390 net/socket.c:1899
  SYSC_setsockopt net/socket.c:1914 [inline]
  SyS_setsockopt+0x34/0x50 net/socket.c:1911

Add rcu locking around call to rt6_check_expired in
ip6_negative_advice.

Fixes: a68886a69180 ("net/ipv6: Make from in rt6_info rcu protected")
Reported-by: syzbot+2422c9e35796659d2...@syzkaller.appspotmail.com
Signed-off-by: David Ahern <dsah...@gmail.com>
---
 net/ipv6/route.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 0407bbc5a028..354a5b8d016f 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -2201,10 +2201,12 @@ static struct dst_entry *ip6_negative_advice(struct 
dst_entry *dst)
 
        if (rt) {
                if (rt->rt6i_flags & RTF_CACHE) {
+                       rcu_read_lock();
                        if (rt6_check_expired(rt)) {
                                rt6_remove_exception_rt(rt);
                                dst = NULL;
                        }
+                       rcu_read_unlock();
                } else {
                        dst_release(dst);
                        dst = NULL;
-- 
2.11.0