veth: Fix use after free in XDP_REDIRECT

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

veth: Fix use after free in XDP_REDIRECT

Commit 718a18a0c8a6 ("veth: Rework veth_xdp_rcv_skb in order
to accept non-linear skb") introduced a bug where it tried to
use pskb_expand_head() if the headroom was less than
XDP_PACKET_HEADROOM. This however uses kmalloc to expand the head,
which will later allow consume_skb() to free the skb while is it still
in use by AF_XDP.

Previously if the headroom was less than XDP_PACKET_HEADROOM we
continued on to allocate a new skb from pages so this restores that
behavior.

BUG: KASAN: use-after-free in __xsk_rcv+0x18d/0x2c0
Read of size 78 at addr ffff888976250154 by task napi/iconduit-g/148640

CPU: 5 PID: 148640 Comm: napi/iconduit-g Kdump: loaded Tainted: G O 6.1.4-cloudflare-kasan-2023.1.2 #1
Hardware name: Quanta Computer Inc. QuantaPlex T41S-2U/S2S-MB, BIOS S2S_3B10.03 06/21/2018
Call Trace:
<TASK>
dump_stack_lvl+0x34/0x48
print_report+0x170/0x473
? __xsk_rcv+0x18d/0x2c0
kasan_report+0xad/0x130
? __xsk_rcv+0x18d/0x2c0
kasan_check_range+0x149/0x1a0
memcpy+0x20/0x60
__xsk_rcv+0x18d/0x2c0
__xsk_map_redirect+0x1f3/0x490
? veth_xdp_rcv_skb+0x89c/0x1ba0 [veth]
xdp_do_redirect+0x5ca/0xd60
veth_xdp_rcv_skb+0x935/0x1ba0 [veth]
? __netif_receive_skb_list_core+0x671/0x920
? veth_xdp+0x670/0x670 [veth]
veth_xdp_rcv+0x304/0xa20 [veth]
? do_xdp_generic+0x150/0x150
? veth_xdp_rcv_one+0xde0/0xde0 [veth]
? _raw_spin_lock_bh+0xe0/0xe0
? newidle_balance+0x887/0xe30
? __perf_event_task_sched_in+0xdb/0x800
veth_poll+0x139/0x571 [veth]
? veth_xdp_rcv+0xa20/0xa20 [veth]
? _raw_spin_unlock+0x39/0x70
? finish_task_switch.isra.0+0x17e/0x7d0
? __switch_to+0x5cf/0x1070
? __schedule+0x95b/0x2640
? io_schedule_timeout+0x160/0x160
__napi_poll+0xa1/0x440
napi_threaded_poll+0x3d1/0x460
? __napi_poll+0x440/0x440
? __kthread_parkme+0xc6/0x1f0
? __napi_poll+0x440/0x440
kthread+0x2a2/0x340
? kthread_complete_and_exit+0x20/0x20
ret_from_fork+0x22/0x30
</TASK>

Freed by task 148640:
kasan_save_stack+0x23/0x50
kasan_set_track+0x21/0x30
kasan_save_free_info+0x2a/0x40
____kasan_slab_free+0x169/0x1d0
slab_free_freelist_hook+0xd2/0x190
__kmem_cache_free+0x1a1/0x2f0
skb_release_data+0x449/0x600
consume_skb+0x9f/0x1c0
veth_xdp_rcv_skb+0x89c/0x1ba0 [veth]
veth_xdp_rcv+0x304/0xa20 [veth]
veth_poll+0x139/0x571 [veth]
__napi_poll+0xa1/0x440
napi_threaded_poll+0x3d1/0x460
kthread+0x2a2/0x340
ret_from_fork+0x22/0x30

The buggy address belongs to the object at ffff888976250000
which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 340 bytes inside of
2048-byte region [ffff888976250000, ffff888976250800)

The buggy address belongs to the physical page:
page:00000000ae18262a refcount:2 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x976250
head:00000000ae18262a order:3 compound_mapcount:0 compound_pincount:0
flags: 0x2ffff800010200(slab|head|node=0|zone=2|lastcpupid=0x1ffff)
raw: 002ffff800010200 0000000000000000 dead000000000122 ffff88810004cf00
raw: 0000000000000000 0000000080080008 00000002ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff888976250000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888976250080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff888976250100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff888976250180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888976250200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb