net: sched: fix memory leak in tcindex_set_parms

In the Linux kernel, the following vulnerability has been resolved:

net: sched: fix memory leak in tcindex_set_parms

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.

Yet the problem is that, during the process of changing,

if `old_r` is retrieved from `p->perfect`, then

kernel uses tcindex_alloc_perfect_hash() to newly

allocate filter results, uses tcindex_filter_result_init()

to clear the old filter result, without destroying

its tcf_exts structure, which triggers the above memory leak.

To be more specific, there are only two source for the `old_r`,

according to the tcindex_lookup(). `old_r` is retrieved from

`p->perfect`, or `old_r` is retrieved from `p->h`.

* If `old_r` is retrieved from `p->perfect`, kernel uses

tcindex_alloc_perfect_hash() to newly allocate the

filter results. Then `r` is assigned with `cp->perfect + handle`,

which is newly allocated. So condition `old_r && old_r != r` is

true in this situation, and kernel uses tcindex_filter_result_init()

to clear the old filter result, without destroying

its tcf_exts structure

* If `old_r` is retrieved from `p->h`, then `p->perfect` is NULL

according to the tcindex_lookup(). Considering that `cp->h`

is directly copied from `p->h` and `p->perfect` is NULL,

`r` is assigned with `tcindex_lookup(cp, handle)`, whose value

should be the same as `old_r`, so condition `old_r && old_r != r`

is false in this situation, kernel ignores using

tcindex_filter_result_init() to clear the old filter result.

So only when `old_r` is retrieved from `p->perfect` does kernel use

tcindex_filter_result_init() to clear the old filter result, which

triggers the above memory leak.

Considering that there already exists a tc_filter_wq workqueue

to destroy the old tcindex_d

---truncated---