[PATCH AUTOSEL 4.4 03/22] media: pci: ttpci: av7110: fix possible buffer overflow caused by bad DMA value in debiirq()

[Sasha Levin <sashal@kernel.org>]

From: Jia-Ju Bai <baijiaju@tsinghua.edu.cn>

[ Upstream commit 6499a0db9b0f1e903d52f8244eacc1d4be00eea2 ]

The value av7110->debi_virt is stored in DMA memory, and it is assigned
to data, and thus data[0] can be modified at any time by malicious
hardware. In this case, "if (data[0] < 2)" can be passed, but then
data[0] can be changed into a large number, which may cause buffer
overflow when the code "av7110->ci_slot[data[0]]" is used.

To fix this possible bug, data[0] is assigned to a local variable, which
replaces the use of data[0].

Signed-off-by: Jia-Ju Bai <baijiaju@tsinghua.edu.cn>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/media/pci/ttpci/av7110.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/media/pci/ttpci/av7110.c b/drivers/media/pci/ttpci/av7110.c
index f89364951ebdf..fb13cc3c591da 100644
--- a/drivers/media/pci/ttpci/av7110.c
+++ b/drivers/media/pci/ttpci/av7110.c
@@ -426,14 +426,15 @@ static void debiirq(unsigned long cookie)
 	case DATA_CI_GET:
 	{
 		u8 *data = av7110->debi_virt;
+		u8 data_0 = data[0];
 
-		if ((data[0] < 2) && data[2] == 0xff) {
+		if (data_0 < 2 && data[2] == 0xff) {
 			int flags = 0;
 			if (data[5] > 0)
 				flags |= CA_CI_MODULE_PRESENT;
 			if (data[5] > 5)
 				flags |= CA_CI_MODULE_READY;
-			av7110->ci_slot[data[0]].flags = flags;
+			av7110->ci_slot[data_0].flags = flags;
 		} else
 			ci_get_data(&av7110->ci_rbuffer,
 				    av7110->debi_virt,
-- 
2.25.1