[PATCH] 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 will uses tcindex_change() to change an existing
traffic-control-indices filter properties. During the
process of changing, kernel will clears the old
traffic-control-indices filter result, and updates it
by RCU assigning new traffic-control-indices data.

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

This patch solves it by using tcf_exts_destroy() to
destroy the tcf_exts structure in old
traffic-control-indices filter result.

Link: https://lore.kernel.org/all/0000000000001de5c505ebc9ec59@xxxxxxxxxx/
Reported-by: syzbot+232ebdbd36706c965ebf@xxxxxxxxxxxxxxxxxxxxxxxxx
Tested-by: syzbot+232ebdbd36706c965ebf@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Hawkins Jiawei <yin31149@xxxxxxxxx>
---
 net/sched/cls_tcindex.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/net/sched/cls_tcindex.c b/net/sched/cls_tcindex.c
index 1c9eeb98d826..dc872a794337 100644
--- a/net/sched/cls_tcindex.c
+++ b/net/sched/cls_tcindex.c
@@ -338,6 +338,9 @@ tcindex_set_parms(struct net *net, struct tcf_proto *tp, unsigned long base,
 	struct tcf_result cr = {};
 	int err, balloc = 0;
 	struct tcf_exts e;
+#ifdef CONFIG_NET_CLS_ACT
+	struct tcf_exts old_e = {};
+#endif
 
 	err = tcf_exts_init(&e, net, TCA_TCINDEX_ACT, TCA_TCINDEX_POLICE);
 	if (err < 0)
@@ -479,6 +482,14 @@ tcindex_set_parms(struct net *net, struct tcf_proto *tp, unsigned long base,
 	}
 
 	if (old_r && old_r != r) {
+#ifdef CONFIG_NET_CLS_ACT
+		/* r->exts is not copied from old_r->exts, and
+		 * the following code will clears the old_r, so
+		 * we need to destroy it after updating the tp->root,
+		 * to avoid memory leak bug.
+		 */
+		old_e = old_r->exts;
+#endif
 		err = tcindex_filter_result_init(old_r, cp, net);
 		if (err < 0) {
 			kfree(f);
@@ -510,6 +521,9 @@ tcindex_set_parms(struct net *net, struct tcf_proto *tp, unsigned long base,
 		tcf_exts_destroy(&new_filter_result.exts);
 	}
 
+#ifdef CONFIG_NET_CLS_ACT
+	tcf_exts_destroy(&old_e);
+#endif
 	if (oldp)
 		tcf_queue_work(&oldp->rwork, tcindex_partial_destroy_work);
 	return 0;
-- 
2.25.1