net/sched: cls_u32: No longer copy tcf_result on update to avoid use-after-free

When u32_change() is called on an existing filter, the whole
tcf_result struct is always copied into the new instance of the filter.

This causes a problem when updating a filter bound to a class,
as tcf_unbind_filter() is always called on the old instance in the
success path, decreasing filter_cnt of the still referenced class
and allowing it to be deleted, leading to a use-after-free.

Fix this by no longer copying the tcf_result struct from the old filter.

Fixes: de5df63228fc ("net: sched: cls_u32 changes to knode must appear atomic to readers")
Reported-by: valis <sec@valis.email>
Reported-by: M A Ramdhan <ramdhan@starlabs.sg>
Signed-off-by: valis <sec@valis.email>
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
Reviewed-by: Victor Nogueira <victor@mojatatu.com>
Reviewed-by: Pedro Tammela <pctammela@mojatatu.com>
Reviewed-by: M A Ramdhan <ramdhan@starlabs.sg>
Link: https://lore.kernel.org/r/20230729123202.72406-2-jhs@mojatatu.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
index 907e588..da4c179 100644 (file)
--- a/net/sched/cls_u32.c
+++ b/net/sched/cls_u32.c
@@ -826,7 +826,6 @@ static struct tc_u_knode *u32_init_knode(struct net *net, struct tcf_proto *tp,
 
        new->ifindex = n->ifindex;
        new->fshift = n->fshift;
-       new->res = n->res;
        new->flags = n->flags;
        RCU_INIT_POINTER(new->ht_down, ht);