[PATCH v3] net: sched: fix memory leak in tcindex_set_parms

[Hawkins Jiawei]

Syzkaller reports a memory leak as follows:
====================================
BUG: memory leak
unreferenced object 0xffff88810c287f00 (size 256):
  comm "syz-executor105", pid 3600, jiffies 4294943292 (age 12.990s)
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  backtrace:
    [<ffffffff814cf9f0>] kmalloc_trace+0x20/0x90 mm/slab_common.c:1046
    [<ffffffff839c9e07>] kmalloc include/linux/slab.h:576 [inline]
    [<ffffffff839c9e07>] kmalloc_array include/linux/slab.h:627 [inline]
    [<ffffffff839c9e07>] kcalloc include/linux/slab.h:659 [inline]
    [<ffffffff839c9e07>] tcf_exts_init include/net/pkt_cls.h:250 [inline]
    [<ffffffff839c9e07>] tcindex_set_parms+0xa7/0xbe0 net/sched/cls_tcindex.c:342
    [<ffffffff839caa1f>] tcindex_change+0xdf/0x120 net/sched/cls_tcindex.c:553
    [<ffffffff8394db62>] tc_new_tfilter+0x4f2/0x1100 net/sched/cls_api.c:2147
    [<ffffffff8389e91c>] rtnetlink_rcv_msg+0x4dc/0x5d0 net/core/rtnetlink.c:6082
    [<ffffffff839eba67>] netlink_rcv_skb+0x87/0x1d0 net/netlink/af_netlink.c:2540
    [<ffffffff839eab87>] netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
    [<ffffffff839eab87>] netlink_unicast+0x397/0x4c0 net/netlink/af_netlink.c:1345
    [<ffffffff839eb046>] netlink_sendmsg+0x396/0x710 net/netlink/af_netlink.c:1921
    [<ffffffff8383e796>] sock_sendmsg_nosec net/socket.c:714 [inline]
    [<ffffffff8383e796>] sock_sendmsg+0x56/0x80 net/socket.c:734
    [<ffffffff8383eb08>] ____sys_sendmsg+0x178/0x410 net/socket.c:2482
    [<ffffffff83843678>] ___sys_sendmsg+0xa8/0x110 net/socket.c:2536
    [<ffffffff838439c5>] __sys_sendmmsg+0x105/0x330 net/socket.c:2622
    [<ffffffff83843c14>] __do_sys_sendmmsg net/socket.c:2651 [inline]
    [<ffffffff83843c14>] __se_sys_sendmmsg net/socket.c:2648 [inline]
    [<ffffffff83843c14>] __x64_sys_sendmmsg+0x24/0x30 net/socket.c:2648
    [<ffffffff84605fd5>] do_syscall_x64 arch/x86/entry/common.c:50 [inline]
    [<ffffffff84605fd5>] do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
    [<ffffffff84800087>] entry_SYSCALL_64_after_hwframe+0x63/0xcd
====================================

Kernel uses tcindex_change() to change an existing
filter properties. During the process of changing,
kernel uses tcindex_alloc_perfect_hash() to newly
allocate filter results, uses tcindex_filter_result_init()
to clear the old filter result.

Yet the problem is that, kernel clears the old
filter result, without destroying its tcf_exts structure,
which triggers the above memory leak.

Considering that there already extis a tc_filter_wq workqueue
to destroy the old tcindex_data by tcindex_partial_destroy_work()
at the end of tcindex_set_parms(), this patch solves this memory
leak bug by removing this old filter result clearing part,
and delegating it to the tc_filter_wq workqueue.

[Thanks to the suggestion from Jakub Kicinski, Cong Wang, Paolo Abeni
and Dmitry Vyukov]

Fixes: b9a24bb76bf6 ("net_sched: properly handle failure case of tcf_exts_init()")
Link: https://lore.kernel.org/all/0000000000001de5c505ebc9ec59@xxxxxxxxxx/
Reported-by: syzbot+232ebdbd36706c965ebf@xxxxxxxxxxxxxxxxxxxxxxxxx
Tested-by: syzbot+232ebdbd36706c965ebf@xxxxxxxxxxxxxxxxxxxxxxxxx
Cc: Cong Wang <cong.wang@xxxxxxxxxxxxx>
Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
Cc: Paolo Abeni <pabeni@xxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx> 
Signed-off-by: Hawkins Jiawei <yin31149@xxxxxxxxx>
---
v3:
  - refactor the commit message
  - delegate the tcf_exts_destroy() to tc_filter_wq workqueue,
suggested by Paolo Abeni and Dmitry Vyukov

v2: https://lore.kernel.org/all/20221113170507.8205-1-yin31149@xxxxxxxxx/

v1: https://lore.kernel.org/all/20221031060835.11722-1-yin31149@xxxxxxxxx/

 net/sched/cls_tcindex.c | 8 --------
 1 file changed, 8 deletions(-)

diff --git a/net/sched/cls_tcindex.c b/net/sched/cls_tcindex.c
index 1c9eeb98d826..3f4e7a6cdd96 100644
--- a/net/sched/cls_tcindex.c
+++ b/net/sched/cls_tcindex.c
@@ -478,14 +478,6 @@ tcindex_set_parms(struct net *net, struct tcf_proto *tp, unsigned long base,
 		tcf_bind_filter(tp, &cr, base);
 	}
 
-	if (old_r && old_r != r) {
-		err = tcindex_filter_result_init(old_r, cp, net);
-		if (err < 0) {
-			kfree(f);
-			goto errout_alloc;
-		}
-	}
-
 	oldp = p;
 	r->res = cr;
 	tcf_exts_change(&r->exts, &e);
-- 
2.34.1