cfg80211: fix cmp_ies

When comparing two items by IE, the sort order
wasn't stable, which could lead to issues in the
rbtree. Make it stable by making a missing IE
sort before a present IE.

Also sort by length first if it differs and then
by contents.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 8 insertions, 5 deletions

diff --git a/net/wireless/scan.c b/net/wireless/scan.c
index 0fb142410404..dc23b31594e0 100644
--- a/net/wireless/scan.c
+++ b/net/wireless/scan.c
@@ -259,17 +259,20 @@ static int cmp_ies(u8 num, u8 *ies1, size_t len1, u8 *ies2, size_t len2)
 {
         const u8 *ie1 = cfg80211_find_ie(num, ies1, len1);
         const u8 *ie2 = cfg80211_find_ie(num, ies2, len2);
-        int r;
 
+        /* equal if both missing */
         if (!ie1 && !ie2)
                 return 0;
-        if (!ie1 || !ie2)
+        /* sort missing IE before (left of) present IE */
+        if (!ie1)
                 return -1;
+        if (!ie2)
+                return 1;
 
-        r = memcmp(ie1 + 2, ie2 + 2, min(ie1[1], ie2[1]));
-        if (r == 0 && ie1[1] != ie2[1])
+        /* sort by length first, then by contents */
+        if (ie1[1] != ie2[1])
                 return ie2[1] - ie1[1];
-        return r;
+        return memcmp(ie1 + 2, ie2 + 2, ie1[1]);
 }
 
 static bool is_bss(struct cfg80211_bss *a,