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: [] kmalloc_trace+0x20/0x90 mm/slab_common.c:1046 [] kmalloc include/linux/slab.h:576 [inline] [] kmalloc_array include/linux/slab.h:627 [inline] [] kcalloc include/linux/slab.h:659 [inline] [] tcf_exts_init include/net/pkt_cls.h:250 [inline] [] tcindex_set_parms+0xa7/0xbe0 net/sched/cls_tcindex.c:342 [] tcindex_change+0xdf/0x120 net/sched/cls_tcindex.c:553 [] tc_new_tfilter+0x4f2/0x1100 net/sched/cls_api.c:2147 [] rtnetlink_rcv_msg+0x4dc/0x5d0 net/core/rtnetlink.c:6082 [] netlink_rcv_skb+0x87/0x1d0 net/netlink/af_netlink.c:2540 [] netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline] [] netlink_unicast+0x397/0x4c0 net/netlink/af_netlink.c:1345 [] netlink_sendmsg+0x396/0x710 net/netlink/af_netlink.c:1921 [] sock_sendmsg_nosec net/socket.c:714 [inline] [] sock_sendmsg+0x56/0x80 net/socket.c:734 [] ____sys_sendmsg+0x178/0x410 net/socket.c:2482 [] ___sys_sendmsg+0xa8/0x110 net/socket.c:2536 [] __sys_sendmmsg+0x105/0x330 net/socket.c:2622 [] __do_sys_sendmmsg net/socket.c:2651 [inline] [] __se_sys_sendmmsg net/socket.c:2648 [inline] [] __x64_sys_sendmmsg+0x24/0x30 net/socket.c:2648 [] do_syscall_x64 arch/x86/entry/common.c:50 [inline] [] do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 [] 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---