net_sched: keep alloc_hash updated after hash allocation

BugLink: https://bugs.launchpad.net/bugs/1873852

[ Upstream commit 0d1c3530 ]

In commit 599be01e ("net_sched: fix an OOB access in cls_tcindex")
I moved cp->hash calculation before the first
tcindex_alloc_perfect_hash(), but cp->alloc_hash is left untouched.
This difference could lead to another out of bound access.

cp->alloc_hash should always be the size allocated, we should
update it after this tcindex_alloc_perfect_hash().

Reported-and-tested-by: syzbot+dcc34d54d68ef7d2d53d@syzkaller.appspotmail.com
Reported-and-tested-by: syzbot+c72da7b9ed57cde6fca2@syzkaller.appspotmail.com
Fixes: 599be01e ("net_sched: fix an OOB access in cls_tcindex")
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Kelsey Skunberg <kelsey.skunberg@canonical.com>

net/sched/cls_tcindex.c

@@ -293,6 +293,7 @@ tcindex_set_parms(struct net *net, struct tcf_proto *tp, unsigned long base,
 				      sizeof(*r) * cp->hash, GFP_KERNEL);
 		if (!cp->perfect)
 			goto errout;
+		cp->alloc_hash = cp->hash;
 		for (i = 0; i < min(cp->hash, p->hash); i++)
 			tcf_exts_init(&cp->perfect[i].exts,
 				      TCA_TCINDEX_ACT, TCA_TCINDEX_POLICE);