[PATCH 2/2] padata: fix UAF in padata_reorder

[Chen Ridong]

From: Chen Ridong <chenridong@xxxxxxxxxx>

A bug was found when run ltp test:

BUG: KASAN: slab-use-after-free in padata_find_next+0x29/0x1a0
Read of size 4 at addr ffff88bbfe003524 by task kworker/u113:2/3039206

CPU: 0 PID: 3039206 Comm: kworker/u113:2 Kdump: loaded Not tainted 6.6.0+
Workqueue: pdecrypt_parallel padata_parallel_worker
Call Trace:
<TASK>
dump_stack_lvl+0x32/0x50
print_address_description.constprop.0+0x6b/0x3d0
print_report+0xdd/0x2c0
kasan_report+0xa5/0xd0
padata_find_next+0x29/0x1a0
padata_reorder+0x131/0x220
padata_parallel_worker+0x3d/0xc0
process_one_work+0x2ec/0x5a0

If 'mdelay(10)' is added before calling 'padata_find_next' in the
'padata_reorder' function, this issue could be reproduced easily with
ltp test (pcrypt_aead01).

This can be explained as bellow:

pcrypt_aead_encrypt
...
padata_do_parallel
refcount_inc(&pd->refcnt); // add refcnt
...
padata_do_serial
padata_reorder // pd
while (1) {
padata_find_next(pd, true); // using pd
queue_work_on
...
padata_serial_worker				crypto_del_alg
padata_put_pd_cnt // sub refcnt
						padata_free_shell
						padata_put_pd(ps->pd);
						// pd is freed
// loop again, but pd is freed
// call padata_find_next, UAF
}

In the padata_reorder function, when it loops in 'while', if the alg is
deleted, the refcnt may be decreased to 0 before entering
'padata_find_next', which leads to UAF, To fix this issue, add refcnt in
the padata_reorder to avoid UAF.

Fixes: b128a3040935 ("padata: allocate workqueue internally")
Signed-off-by: Chen Ridong <chenridong@xxxxxxxxxx>
Signed-off-by: Qu Zicheng <quzicheng@xxxxxxxxxx>
---
 kernel/padata.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/padata.c b/kernel/padata.c
index 5d8e18cdcb25..627014825266 100644
--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -319,6 +319,7 @@ static void padata_reorder(struct parallel_data *pd)
 	if (!spin_trylock_bh(&pd->lock))
 		return;
 
+	padata_get_pd(pd);
 	while (1) {
 		padata = padata_find_next(pd, true);
 
@@ -355,6 +356,7 @@ static void padata_reorder(struct parallel_data *pd)
 	reorder = per_cpu_ptr(pd->reorder_list, pd->cpu);
 	if (!list_empty(&reorder->list) && padata_find_next(pd, false))
 		queue_work(pinst->serial_wq, &pd->reorder_work);
+	padata_put_pd(pd);
 }
 
 static void invoke_padata_reorder(struct work_struct *work)
-- 
2.34.1