linux-kernel - [PATCH v3] nl80211: take RCU read lock when calling ieee80211_bss_get

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Date:   Mon, 15 Jan 2018 08:12:15 +0100
From:   Dominik Brodowski <linux@...inikbrodowski.net>
To:     Johannes Berg <johannes@...solutions.net>
Cc:     regressions@...mhuis.info, netdev@...r.kernel.org,
        linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v3] nl80211: take RCU read lock when calling
 ieee80211_bss_get_ie()

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>
---

> but after, perhaps it's easier to just do
> 
> 		if (ssid_ie &&
> 		    nla_put(...)
> 			goto nla_put_failure_rcu_locked;
> 
> and avoid the extra label (but yeah, it's getting late)

OK, done that (and updated the commit message), and testet it.

Thanks,
	Dominik

diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
index 2b3dbcd40e46..ed87a97fcb0b 100644
--- a/net/wireless/nl80211.c
+++ b/net/wireless/nl80211.c
@@ -2618,12 +2618,13 @@ static int nl80211_send_iface(struct sk_buff *msg, u32 portid, u32 seq, int flag
 		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:
@@ -2635,6 +2636,8 @@ static int nl80211_send_iface(struct sk_buff *msg, u32 portid, u32 seq, int flag
 	genlmsg_end(msg, hdr);
 	return 0;
 
+ nla_put_failure_rcu_locked:
+	rcu_read_unlock();
  nla_put_failure_locked:
 	wdev_unlock(wdev);
  nla_put_failure: