[PATCH 2/2] [media] saa7164: fix double fetch PCIe access condition

[Paolo Pisati]

From: Steven Toth <stoth at kernellabs.com>

CVE-2017-8831

Avoid a double fetch by reusing the values from the prior transfer.

Originally reported via https://bugzilla.kernel.org/show_bug.cgi?id=195559

Thanks to Pengfei Wang <wpengfeinudt at gmail.com> for reporting.

Signed-off-by: Steven Toth <stoth at kernellabs.com>
Reported-by: Pengfei Wang <wpengfeinudt at gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab at s-opensource.com>
(cherry picked from commit 6fb05e0dd32e566facb96ea61a48c7488daa5ac3)
Signed-off-by: Paolo Pisati <paolo.pisati at canonical.com>
---
 drivers/media/pci/saa7164/saa7164-bus.c | 13 +------------
 1 file changed, 1 insertion(+), 12 deletions(-)

diff --git a/drivers/media/pci/saa7164/saa7164-bus.c b/drivers/media/pci/saa7164/saa7164-bus.c
index 6c73f5b..1c779ea 100644
--- a/drivers/media/pci/saa7164/saa7164-bus.c
+++ b/drivers/media/pci/saa7164/saa7164-bus.c
@@ -393,11 +393,11 @@ int saa7164_bus_get(struct saa7164_dev *dev, struct tmComResInfo* msg,
 	msg_tmp.size = le16_to_cpu((__force __le16)msg_tmp.size);
 	msg_tmp.command = le32_to_cpu((__force __le32)msg_tmp.command);
 	msg_tmp.controlselector = le16_to_cpu((__force __le16)msg_tmp.controlselector);
+	memcpy(msg, &msg_tmp, sizeof(*msg));
 
 	/* No need to update the read positions, because this was a peek */
 	/* If the caller specifically want to peek, return */
 	if (peekonly) {
-		memcpy(msg, &msg_tmp, sizeof(*msg));
 		goto peekout;
 	}
 
@@ -442,21 +442,15 @@ int saa7164_bus_get(struct saa7164_dev *dev, struct tmComResInfo* msg,
 		space_rem = bus->m_dwSizeGetRing - curr_grp;
 
 		if (space_rem < sizeof(*msg)) {
-			/* msg wraps around the ring */
-			memcpy_fromio(msg, bus->m_pdwGetRing + curr_grp, space_rem);
-			memcpy_fromio((u8 *)msg + space_rem, bus->m_pdwGetRing,
-				sizeof(*msg) - space_rem);
 			if (buf)
 				memcpy_fromio(buf, bus->m_pdwGetRing + sizeof(*msg) -
 					space_rem, buf_size);
 
 		} else if (space_rem == sizeof(*msg)) {
-			memcpy_fromio(msg, bus->m_pdwGetRing + curr_grp, sizeof(*msg));
 			if (buf)
 				memcpy_fromio(buf, bus->m_pdwGetRing, buf_size);
 		} else {
 			/* Additional data wraps around the ring */
-			memcpy_fromio(msg, bus->m_pdwGetRing + curr_grp, sizeof(*msg));
 			if (buf) {
 				memcpy_fromio(buf, bus->m_pdwGetRing + curr_grp +
 					sizeof(*msg), space_rem - sizeof(*msg));
@@ -469,15 +463,10 @@ int saa7164_bus_get(struct saa7164_dev *dev, struct tmComResInfo* msg,
 
 	} else {
 		/* No wrapping */
-		memcpy_fromio(msg, bus->m_pdwGetRing + curr_grp, sizeof(*msg));
 		if (buf)
 			memcpy_fromio(buf, bus->m_pdwGetRing + curr_grp + sizeof(*msg),
 				buf_size);
 	}
-	/* Convert from little endian to CPU */
-	msg->size = le16_to_cpu((__force __le16)msg->size);
-	msg->command = le32_to_cpu((__force __le32)msg->command);
-	msg->controlselector = le16_to_cpu((__force __le16)msg->controlselector);
 
 	/* Update the read positions, adjusting the ring */
 	saa7164_writel(bus->m_dwGetReadPos, new_grp);
-- 
2.7.4