From: Cong Wang <xiyou.wangcong@xxxxxxxxx> [ Upstream commit ef299cc3fa1a9e1288665a9fdc8bff55629fd359 ] route4_change() allocates a new filter and copies values from the old one. After the new filter is inserted into the hash table, the old filter should be removed and freed, as the final step of the update. However, the current code mistakenly removes the new one. This looks apparently wrong to me, and it causes double "free" and use-after-free too, as reported by syzbot. Reported-and-tested-by: syzbot+f9b32aaacd60305d9687@xxxxxxxxxxxxxxxxxxxxxxxxx Reported-and-tested-by: syzbot+2f8c233f131943d6056d@xxxxxxxxxxxxxxxxxxxxxxxxx Reported-and-tested-by: syzbot+9c2df9fd5e9445b74e01@xxxxxxxxxxxxxxxxxxxxxxxxx Fixes: 1109c00547fc ("net: sched: RCU cls_route") Cc: Jamal Hadi Salim <jhs@xxxxxxxxxxxx> Cc: Jiri Pirko <jiri@xxxxxxxxxxx> Cc: John Fastabend <john.fastabend@xxxxxxxxx> Signed-off-by: Cong Wang <xiyou.wangcong@xxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- net/sched/cls_route.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- a/net/sched/cls_route.c +++ b/net/sched/cls_route.c @@ -540,8 +540,8 @@ static int route4_change(struct net *net fp = &b->ht[h]; for (pfp = rtnl_dereference(*fp); pfp; fp = &pfp->next, pfp = rtnl_dereference(*fp)) { - if (pfp == f) { - *fp = f->next; + if (pfp == fold) { + rcu_assign_pointer(*fp, fold->next); break; } }