CVE-2024-41040 net/sched: Fix UAF when resolving a clash

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

net/sched: Fix UAF when resolving a clash

KASAN reports the following UAF:

BUG: KASAN: slab-use-after-free in tcf_ct_flow_table_process_conn+0x12b/0x380 [act_ct]
Read of size 1 at addr ffff888c07603600 by task handler130/6469

Call Trace:
<IRQ>
dump_stack_lvl+0x48/0x70
print_address_description.constprop.0+0x33/0x3d0
print_report+0xc0/0x2b0
kasan_report+0xd0/0x120
__asan_load1+0x6c/0x80
tcf_ct_flow_table_process_conn+0x12b/0x380 [act_ct]
tcf_ct_act+0x886/0x1350 [act_ct]
tcf_action_exec+0xf8/0x1f0
fl_classify+0x355/0x360 [cls_flower]
__tcf_classify+0x1fd/0x330
tcf_classify+0x21c/0x3c0
sch_handle_ingress.constprop.0+0x2c5/0x500
__netif_receive_skb_core.constprop.0+0xb25/0x1510
__netif_receive_skb_list_core+0x220/0x4c0
netif_receive_skb_list_internal+0x446/0x620
napi_complete_done+0x157/0x3d0
gro_cell_poll+0xcf/0x100
__napi_poll+0x65/0x310
net_rx_action+0x30c/0x5c0
__do_softirq+0x14f/0x491
__irq_exit_rcu+0x82/0xc0
irq_exit_rcu+0xe/0x20
common_interrupt+0xa1/0xb0
</IRQ>
<TASK>
asm_common_interrupt+0x27/0x40

Allocated by task 6469:
kasan_save_stack+0x38/0x70
kasan_set_track+0x25/0x40
kasan_save_alloc_info+0x1e/0x40
__kasan_krealloc+0x133/0x190
krealloc+0xaa/0x130
nf_ct_ext_add+0xed/0x230 [nf_conntrack]
tcf_ct_act+0x1095/0x1350 [act_ct]
tcf_action_exec+0xf8/0x1f0
fl_classify+0x355/0x360 [cls_flower]
__tcf_classify+0x1fd/0x330
tcf_classify+0x21c/0x3c0
sch_handle_ingress.constprop.0+0x2c5/0x500
__netif_receive_skb_core.constprop.0+0xb25/0x1510
__netif_receive_skb_list_core+0x220/0x4c0
netif_receive_skb_list_internal+0x446/0x620
napi_complete_done+0x157/0x3d0
gro_cell_poll+0xcf/0x100
__napi_poll+0x65/0x310
net_rx_action+0x30c/0x5c0
__do_softirq+0x14f/0x491

Freed by task 6469:
kasan_save_stack+0x38/0x70
kasan_set_track+0x25/0x40
kasan_save_free_info+0x2b/0x60
____kasan_slab_free+0x180/0x1f0
__kasan_slab_free+0x12/0x30
slab_free_freelist_hook+0xd2/0x1a0
__kmem_cache_free+0x1a2/0x2f0
kfree+0x78/0x120
nf_conntrack_free+0x74/0x130 [nf_conntrack]
nf_ct_destroy+0xb2/0x140 [nf_conntrack]
__nf_ct_resolve_clash+0x529/0x5d0 [nf_conntrack]
nf_ct_resolve_clash+0xf6/0x490 [nf_conntrack]
__nf_conntrack_confirm+0x2c6/0x770 [nf_conntrack]
tcf_ct_act+0x12ad/0x1350 [act_ct]
tcf_action_exec+0xf8/0x1f0
fl_classify+0x355/0x360 [cls_flower]
__tcf_classify+0x1fd/0x330
tcf_classify+0x21c/0x3c0
sch_handle_ingress.constprop.0+0x2c5/0x500
__netif_receive_skb_core.constprop.0+0xb25/0x1510
__netif_receive_skb_list_core+0x220/0x4c0
netif_receive_skb_list_internal+0x446/0x620
napi_complete_done+0x157/0x3d0
gro_cell_poll+0xcf/0x100
__napi_poll+0x65/0x310
net_rx_action+0x30c/0x5c0
__do_softirq+0x14f/0x491

The ct may be dropped if a clash has been resolved but is still passed to
the tcf_ct_flow_table_process_conn function for further usage. This issue
can be fixed by retrieving ct from skb again after confirming conntrack.