[PATCH 4.4 066/143] isdn: hisax: hfc_pci: Fix a possible concurrency use-after-free bug in HFCPCI_l1hw()

From: Greg Kroah-Hartman
Date: Mon Feb 18 2019 - 09:03:44 EST

4.4-stable review patch. If anyone has any objections, please let me know.


[ Upstream commit 7418e6520f22a2e35815122fa5a53d5bbfa2c10f ]

In drivers/isdn/hisax/hfc_pci.c, the functions hfcpci_interrupt() and
HFCPCI_l1hw() may be concurrently executed.

line 1173: if (!cs->tx_skb)

line 942: spin_lock_irqsave();
line 1066: dev_kfree_skb_irq(cs->tx_skb);

Thus, a possible concurrency use-after-free bug may occur
in HFCPCI_l1hw().

To fix these bugs, the calls to spin_lock_irqsave() and
spin_unlock_irqrestore() are added in HFCPCI_l1hw(), to protect the
access to cs->tx_skb.

Signed-off-by: Jia-Ju Bai <baijiaju1990@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
drivers/isdn/hisax/hfc_pci.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/drivers/isdn/hisax/hfc_pci.c b/drivers/isdn/hisax/hfc_pci.c
index 90449e1e91e5..1b1453d62fed 100644
--- a/drivers/isdn/hisax/hfc_pci.c
+++ b/drivers/isdn/hisax/hfc_pci.c
@@ -1169,11 +1169,13 @@ HFCPCI_l1hw(struct PStack *st, int pr, void *arg)
if (cs->debug & L1_DEB_LAPD)
debugl1(cs, "-> PH_REQUEST_PULL");
+ spin_lock_irqsave(&cs->lock, flags);
if (!cs->tx_skb) {
test_and_clear_bit(FLG_L1_PULL_REQ, &st->l1.Flags);
st->l1.l1l2(st, PH_PULL | CONFIRM, NULL);
} else
test_and_set_bit(FLG_L1_PULL_REQ, &st->l1.Flags);
+ spin_unlock_irqrestore(&cs->lock, flags);
spin_lock_irqsave(&cs->lock, flags);