linux-kernel - [PATCH V2] Fix unsafe memory access by memcmp

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Date:   Sun, 3 Apr 2022 22:52:07 -0400
From:   Charlie Sands <sandsch@...thvilleschools.net>
To:     gregkh@...uxfoundation.org
Cc:     Larry.Finger@...inger.net, phil@...lpotter.co.uk,
        linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org,
        paskripkin@...il.com
Subject: [PATCH V2] Fix unsafe memory access by memcmp

This patch fixes sparse warnings about the memcmp function unsafely
accessing userspace memory without first copying it to kernel space.

Signed-off-by: Charlie Sands <sandsch@...thvilleschools.net>
---

V2: Fixed checkpatch.pl warning and changed variable name as suggested
by Greg K. H. and improved error checking on the "copy_from_user" function as
suggested by Pavel Skripkin.

 drivers/staging/r8188eu/os_dep/ioctl_linux.c | 21 ++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/drivers/staging/r8188eu/os_dep/ioctl_linux.c b/drivers/staging/r8188eu/os_dep/ioctl_linux.c
index 7df213856d66..4b4eec2bde96 100644
--- a/drivers/staging/r8188eu/os_dep/ioctl_linux.c
+++ b/drivers/staging/r8188eu/os_dep/ioctl_linux.c
@@ -3233,23 +3233,28 @@ static int rtw_p2p_get(struct net_device *dev,
 			       struct iw_request_info *info,
 			       union iwreq_data *wrqu, char *extra)
 {
-	if (!memcmp(wrqu->data.pointer, "status", 6)) {
+	char wrqu_data[9];
+
+	if (copy_from_user(wrqu_data, wrqu->data.pointer, 9) != 0)
+		return 0;
+
+	if (!memcmp(wrqu_data, "status", 6)) {
 		rtw_p2p_get_status(dev, info, wrqu, extra);
-	} else if (!memcmp(wrqu->data.pointer, "role", 4)) {
+	} else if (!memcmp(wrqu_data, "role", 4)) {
 		rtw_p2p_get_role(dev, info, wrqu, extra);
-	} else if (!memcmp(wrqu->data.pointer, "peer_ifa", 8)) {
+	} else if (!memcmp(wrqu_data, "peer_ifa", 8)) {
 		rtw_p2p_get_peer_ifaddr(dev, info, wrqu, extra);
-	} else if (!memcmp(wrqu->data.pointer, "req_cm", 6)) {
+	} else if (!memcmp(wrqu_data, "req_cm", 6)) {
 		rtw_p2p_get_req_cm(dev, info, wrqu, extra);
-	} else if (!memcmp(wrqu->data.pointer, "peer_deva", 9)) {
+	} else if (!memcmp(wrqu_data, "peer_deva", 9)) {
 		/*	Get the P2P device address when receiving the provision discovery request frame. */
 		rtw_p2p_get_peer_devaddr(dev, info, wrqu, extra);
-	} else if (!memcmp(wrqu->data.pointer, "group_id", 8)) {
+	} else if (!memcmp(wrqu_data, "group_id", 8)) {
 		rtw_p2p_get_groupid(dev, info, wrqu, extra);
-	} else if (!memcmp(wrqu->data.pointer, "peer_deva_inv", 9)) {
+	} else if (!memcmp(wrqu_data, "peer_deva_inv", 9)) {
 		/*	Get the P2P device address when receiving the P2P Invitation request frame. */
 		rtw_p2p_get_peer_devaddr_by_invitation(dev, info, wrqu, extra);
-	} else if (!memcmp(wrqu->data.pointer, "op_ch", 5)) {
+	} else if (!memcmp(wrqu_data, "op_ch", 5)) {
 		rtw_p2p_get_op_ch(dev, info, wrqu, extra);
 	}
 	return 0;
-- 
2.35.1