linux-kernel - [PATCH 3.16 205/254] nl80211: take RCU read lock when calling ieee80211_bss_get

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Message-ID: <lsq.1519831218.631518194@decadent.org.uk>
Date:   Wed, 28 Feb 2018 15:20:18 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Dominik Brodowski" <linux@...inikbrodowski.net>,
        "Johannes Berg" <johannes.berg@...el.com>
Subject: [PATCH 3.16 205/254] nl80211: take RCU read lock when calling
 ieee80211_bss_get_ie()

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

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

From: Dominik Brodowski <linux@...inikbrodowski.net>

commit 7a94b8c2eee7083ddccd0515830f8c81a8e44b1a upstream.

As ieee80211_bss_get_ie() derefences an RCU to return ssid_ie, both
the call to this function and any operation on this variable need
protection by the RCU read lock.

Fixes: 44905265bc15 ("nl80211: don't expose wdev->ssid for most interfaces")
Signed-off-by: Dominik Brodowski <linux@...inikbrodowski.net>
Signed-off-by: Johannes Berg <johannes.berg@...el.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/wireless/nl80211.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

--- a/net/wireless/nl80211.c
+++ b/net/wireless/nl80211.c
@@ -2354,12 +2354,13 @@ static int nl80211_send_iface(struct sk_
 		const u8 *ssid_ie;
 		if (!wdev->current_bss)
 			break;
+		rcu_read_lock();
 		ssid_ie = ieee80211_bss_get_ie(&wdev->current_bss->pub,
 					       WLAN_EID_SSID);
-		if (!ssid_ie)
-			break;
-		if (nla_put(msg, NL80211_ATTR_SSID, ssid_ie[1], ssid_ie + 2))
-			goto nla_put_failure_locked;
+		if (ssid_ie &&
+		    nla_put(msg, NL80211_ATTR_SSID, ssid_ie[1], ssid_ie + 2))
+			goto nla_put_failure_rcu_locked;
+		rcu_read_unlock();
 		break;
 		}
 	default:
@@ -2370,6 +2371,8 @@ static int nl80211_send_iface(struct sk_
 
 	return genlmsg_end(msg, hdr);
 
+ nla_put_failure_rcu_locked:
+	rcu_read_unlock();
  nla_put_failure_locked:
 	wdev_unlock(wdev);
  nla_put_failure: