Date:   Thu, 18 Aug 2022 10:27:54 +0300
From:   Paul Blakey <paulb@...dia.com>
To:     Paul Blakey <paulb@...dia.com>, Oz Shlomo <ozsh@...dia.com>,
        "Pablo Neira Ayuso" <pablo@...filter.org>,
        Roi Dayan <roid@...dia.com>, <netdev@...r.kernel.org>,
        Saeed Mahameed <saeedm@...dia.com>
CC:     <netfilter-devel@...r.kernel.org>
Subject: [PATCH net 1/1] netfilter: flowtable: Fix use after free after freeing flow table

To clear the flow table on flow table free, the following sequence
normally happens in order:
  1) gc_step work is stopped to disable any further stats/del requests.
  2) All flow table entries are set to teardown state.
  3) Run gc_step which will queue HW del work for each flow table entry.
  4) Waiting for the above del work to finish (flush).
  5) Run gc_step again, deleting all entries from the flow table.
  6) Flow table is freed.

But if a flow table entry already has pending HW stats or HW add work
step 3 will not queue HW del work (it will be skipped), step 4 will wait
for the pending add/stats to finish, and step 5 will queue HW del work
which might execute after freeing of the flow table.

To fix the above, add another flush (before step 2 above) to wait for
any pending add/stats work to finish, so next steps will work as expected
(schedule HW del, wait for it, then delete the flow from the flow table).

Stack trace:
[47773.882335] BUG: KASAN: use-after-free in down_read+0x99/0x460
[47773.883634] Write of size 8 at addr ffff888103b45aa8 by task kworker/u20:6/543704
[47773.885634] CPU: 3 PID: 543704 Comm: kworker/u20:6 Not tainted 5.12.0-rc7+ #2
[47773.886745] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009)
[47773.888438] Workqueue: nf_ft_offload_del flow_offload_work_handler [nf_flow_table]
[47773.889727] Call Trace:
[47773.890214]  dump_stack+0xbb/0x107
[47773.890818]  print_address_description.constprop.0+0x18/0x140
[47773.892990]  kasan_report.cold+0x7c/0xd8
[47773.894459]  kasan_check_range+0x145/0x1a0
[47773.895174]  down_read+0x99/0x460
[47773.899706]  nf_flow_offload_tuple+0x24f/0x3c0 [nf_flow_table]
[47773.907137]  flow_offload_work_handler+0x72d/0xbe0 [nf_flow_table]
[47773.913372]  process_one_work+0x8ac/0x14e0
[47773.921325]
[47773.921325] Allocated by task 592159:
[47773.922031]  kasan_save_stack+0x1b/0x40
[47773.922730]  __kasan_kmalloc+0x7a/0x90
[47773.923411]  tcf_ct_flow_table_get+0x3cb/0x1230 [act_ct]
[47773.924363]  tcf_ct_init+0x71c/0x1156 [act_ct]
[47773.925207]  tcf_action_init_1+0x45b/0x700
[47773.925987]  tcf_action_init+0x453/0x6b0
[47773.926692]  tcf_exts_validate+0x3d0/0x600
[47773.927419]  fl_change+0x757/0x4a51 [cls_flower]
[47773.928227]  tc_new_tfilter+0x89a/0x2070
[47773.936652]
[47773.936652] Freed by task 543704:
[47773.937303]  kasan_save_stack+0x1b/0x40
[47773.938039]  kasan_set_track+0x1c/0x30
[47773.938731]  kasan_set_free_info+0x20/0x30
[47773.939467]  __kasan_slab_free+0xe7/0x120
[47773.940194]  slab_free_freelist_hook+0x86/0x190
[47773.941038]  kfree+0xce/0x3a0
[47773.941644]  tcf_ct_flow_table_cleanup_work+0x1b/0x30 [act_ct]
[47773.942656]  process_one_work+0x8ac/0x14e0

Fixes: c29f74e0df7a ("netfilter: nf_flow_table: hardware offload support")
Signed-off-by: Paul Blakey <paulb@...dia.com>
---
 net/netfilter/nf_flow_table_core.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/netfilter/nf_flow_table_core.c b/net/netfilter/nf_flow_table_core.c
index f2def06d1070..19fd3b5f8a1b 100644
--- a/net/netfilter/nf_flow_table_core.c
+++ b/net/netfilter/nf_flow_table_core.c
@@ -605,6 +605,7 @@ void nf_flow_table_free(struct nf_flowtable *flow_table)
 	mutex_unlock(&flowtable_lock);
 
 	cancel_delayed_work_sync(&flow_table->gc_work);
+	nf_flow_table_offload_flush(flow_table);
 	nf_flow_table_iterate(flow_table, nf_flow_table_do_cleanup, NULL);
 	nf_flow_table_iterate(flow_table, nf_flow_offload_gc_step, NULL);
 	nf_flow_table_offload_flush(flow_table);
-- 
2.30.1

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