[PATCH 4.19 04/42] ipv6: fix a dst leak when removing its exception

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Xin Long <lucien.xin@gmail.com>

[ Upstream commit 761f60261b4401aa368d71d431b4c218af0efcee ]

These is no need to hold dst before calling rt6_remove_exception_rt().
The call to dst_hold_safe() in ip6_link_failure() was for ip6_del_rt(),
which has been removed in Commit 93531c674315 ("net/ipv6: separate
handling of FIB entries from dst based routes"). Otherwise, it will
cause a dst leak.

This patch is to simply remove the dst_hold_safe() call before calling
rt6_remove_exception_rt() and also do the same in ip6_del_cached_rt().
It's safe, because the removal of the exception that holds its dst's
refcnt is protected by rt6_exception_lock.

Fixes: 93531c674315 ("net/ipv6: separate handling of FIB entries from dst based routes")
Fixes: 23fb93a4d3f1 ("net/ipv6: Cleanup exception and cache route handling")
Reported-by: Li Shuang <shuali@redhat.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/ipv6/route.c |    7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -2263,8 +2263,7 @@ static void ip6_link_failure(struct sk_b
 	if (rt) {
 		rcu_read_lock();
 		if (rt->rt6i_flags & RTF_CACHE) {
-			if (dst_hold_safe(&rt->dst))
-				rt6_remove_exception_rt(rt);
+			rt6_remove_exception_rt(rt);
 		} else {
 			struct fib6_info *from;
 			struct fib6_node *fn;
@@ -3266,8 +3265,8 @@ static int ip6_del_cached_rt(struct rt6_
 	if (cfg->fc_flags & RTF_GATEWAY &&
 	    !ipv6_addr_equal(&cfg->fc_gateway, &rt->rt6i_gateway))
 		goto out;
-	if (dst_hold_safe(&rt->dst))
-		rc = rt6_remove_exception_rt(rt);
+
+	rc = rt6_remove_exception_rt(rt);
 out:
 	return rc;
 }