[PATCH AUTOSEL 4.20 29/52] cfg80211: prevent speculation on cfg80211_classify8021d() return

[Sasha Levin]

From: Johannes Berg <johannes.b...@intel.com>

[ Upstream commit 1fc9b7253382ce1a83d9a3e63e88d656eb63f263 ]

It's possible that the caller of cfg80211_classify8021d() uses the
value to index an array, like mac80211 in ieee80211_downgrade_queue().
Prevent speculation on the return value.

Signed-off-by: Johannes Berg <johannes.b...@intel.com>
Signed-off-by: Luca Coelho <luciano.coe...@intel.com>
Signed-off-by: Johannes Berg <johannes.b...@intel.com>
Signed-off-by: Sasha Levin <sas...@kernel.org>
---
 net/wireless/util.c | 35 ++++++++++++++++++++++++-----------
 1 file changed, 24 insertions(+), 11 deletions(-)

diff --git a/net/wireless/util.c b/net/wireless/util.c
index d473bd135da8..d8b7eb75bade 100644
--- a/net/wireless/util.c
+++ b/net/wireless/util.c
@@ -5,7 +5,7 @@
  * Copyright 2007-2009 Johannes Berg <johan...@sipsolutions.net>
  * Copyright 2013-2014  Intel Mobile Communications GmbH
  * Copyright 2017      Intel Deutschland GmbH
- * Copyright (C) 2018 Intel Corporation
+ * Copyright (C) 2018-2019 Intel Corporation
  */
 #include <linux/export.h>
 #include <linux/bitops.h>
@@ -19,6 +19,7 @@
 #include <linux/mpls.h>
 #include <linux/gcd.h>
 #include <linux/bitfield.h>
+#include <linux/nospec.h>
 #include "core.h"
 #include "rdev-ops.h"
 
@@ -715,20 +716,25 @@ unsigned int cfg80211_classify8021d(struct sk_buff *skb,
 {
        unsigned int dscp;
        unsigned char vlan_priority;
+       unsigned int ret;
 
        /* skb->priority values from 256->263 are magic values to
         * directly indicate a specific 802.1d priority.  This is used
         * to allow 802.1d priority to be passed directly in from VLAN
         * tags, etc.
         */
-       if (skb->priority >= 256 && skb->priority <= 263)
-               return skb->priority - 256;
+       if (skb->priority >= 256 && skb->priority <= 263) {
+               ret = skb->priority - 256;
+               goto out;
+       }
 
        if (skb_vlan_tag_present(skb)) {
                vlan_priority = (skb_vlan_tag_get(skb) & VLAN_PRIO_MASK)
                        >> VLAN_PRIO_SHIFT;
-               if (vlan_priority > 0)
-                       return vlan_priority;
+               if (vlan_priority > 0) {
+                       ret = vlan_priority;
+                       goto out;
+               }
        }
 
        switch (skb->protocol) {
@@ -747,8 +753,9 @@ unsigned int cfg80211_classify8021d(struct sk_buff *skb,
                if (!mpls)
                        return 0;
 
-               return (ntohl(mpls->entry) & MPLS_LS_TC_MASK)
+               ret = (ntohl(mpls->entry) & MPLS_LS_TC_MASK)
                        >> MPLS_LS_TC_SHIFT;
+               goto out;
        }
        case htons(ETH_P_80221):
                /* 802.21 is always network control traffic */
@@ -761,18 +768,24 @@ unsigned int cfg80211_classify8021d(struct sk_buff *skb,
                unsigned int i, tmp_dscp = dscp >> 2;
 
                for (i = 0; i < qos_map->num_des; i++) {
-                       if (tmp_dscp == qos_map->dscp_exception[i].dscp)
-                               return qos_map->dscp_exception[i].up;
+                       if (tmp_dscp == qos_map->dscp_exception[i].dscp) {
+                               ret = qos_map->dscp_exception[i].up;
+                               goto out;
+                       }
                }
 
                for (i = 0; i < 8; i++) {
                        if (tmp_dscp >= qos_map->up[i].low &&
-                           tmp_dscp <= qos_map->up[i].high)
-                               return i;
+                           tmp_dscp <= qos_map->up[i].high) {
+                               ret = i;
+                               goto out;
+                       }
                }
        }
 
-       return dscp >> 5;
+       ret = dscp >> 5;
+out:
+       return array_index_nospec(ret, IEEE80211_NUM_TIDS);
 }
 EXPORT_SYMBOL(cfg80211_classify8021d);
 
-- 
2.19.1