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

[Cong Wang]

On Mon, Oct 31, 2022 at 02:08:35PM +0800, Hawkins Jiawei wrote:
> 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.

So... your patch can be just the following one-liner, right?


diff --git a/net/sched/cls_tcindex.c b/net/sched/cls_tcindex.c
index 1c9eeb98d826..00a6c04a4b42 100644
--- a/net/sched/cls_tcindex.c
+++ b/net/sched/cls_tcindex.c
@@ -479,6 +479,7 @@ tcindex_set_parms(struct net *net, struct tcf_proto *tp, unsigned long base,
 	}
 
 	if (old_r && old_r != r) {
+		tcf_exts_destroy(&old_r->exts);
 		err = tcindex_filter_result_init(old_r, cp, net);
 		if (err < 0) {
 			kfree(f);