linux-kernel - [PATCH 3.16 24/25] cfg80211: wext: avoid copying malformed SSIDs

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Date:   Tue, 12 Nov 2019 23:48:21 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Nicolas Waisman" <nico@...mle.com>,
        "Will Deacon" <will@...nel.org>,
        "Johannes Berg" <johannes.berg@...el.com>,
        "Kees Cook" <keescook@...omium.org>
Subject: [PATCH 3.16 24/25] cfg80211: wext: avoid copying malformed SSIDs

3.16.77-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Will Deacon <will@...nel.org>

commit 4ac2813cc867ae563a1ba5a9414bfb554e5796fa upstream.

Ensure the SSID element is bounds-checked prior to invoking memcpy()
with its length field, when copying to userspace.

Cc: Kees Cook <keescook@...omium.org>
Reported-by: Nicolas Waisman <nico@...mle.com>
Signed-off-by: Will Deacon <will@...nel.org>
Link: https://lore.kernel.org/r/20191004095132.15777-2-will@kernel.org
[adjust commit log a bit]
Signed-off-by: Johannes Berg <johannes.berg@...el.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/wireless/wext-sme.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/net/wireless/wext-sme.c
+++ b/net/wireless/wext-sme.c
@@ -225,6 +225,7 @@ int cfg80211_mgd_wext_giwessid(struct ne
 			       struct iw_point *data, char *ssid)
 {
 	struct wireless_dev *wdev = dev->ieee80211_ptr;
+	int ret = 0;
 
 	/* call only for station! */
 	if (WARN_ON(wdev->iftype != NL80211_IFTYPE_STATION))
@@ -242,7 +243,10 @@ int cfg80211_mgd_wext_giwessid(struct ne
 		if (ie) {
 			data->flags = 1;
 			data->length = ie[1];
-			memcpy(ssid, ie + 2, data->length);
+			if (data->length > IW_ESSID_MAX_SIZE)
+				ret = -EINVAL;
+			else
+				memcpy(ssid, ie + 2, data->length);
 		}
 		rcu_read_unlock();
 	} else if (wdev->wext.connect.ssid && wdev->wext.connect.ssid_len) {
@@ -252,7 +256,7 @@ int cfg80211_mgd_wext_giwessid(struct ne
 	}
 	wdev_unlock(wdev);
 
-	return 0;
+	return ret;
 }
 
 int cfg80211_mgd_wext_siwap(struct net_device *dev,