HE: Fix set_he_cap() parsing of config options for MU EDCA Params

When I replaced the POS() function with ffs() when applying relevant
parts from the original patch, this ended up breaking the frame
construction since the POS() function was supposed to count the bit
offset for the mask with 0 being the LSB instead of 1 returned by ffs().
Furthermore, ffs() is not available in all C libraries (e.g., not
directly exposed by strings.h on Android), so better not depend on that
or compiler builtins for this since there is no need for this to be as
fast as possible in configuration parsing.

Fix this with a simple function to determine the number of bits the
value needs to be shifted left to align with the mask.

Fixes: 11ce7a1bc3e2 ("HE: Add MU EDCA Parameter Set element (AP)")
Signed-off-by: Jouni Malinen <jouni@codeaurora.org>

diff --git a/hostapd/config_file.c b/hostapd/config_file.c
index aeec1d9e25d662452f6e8c1567076ec3d9866648..c8ff7a06a3f46960362b9a407c40ccd40ad95519 100644 (file)
--- a/hostapd/config_file.c
+++ b/hostapd/config_file.c
@@ -1380,10 +1380,26 @@ static int hostapd_config_vht_capab(struct hostapd_config *conf,
 
 
 #ifdef CONFIG_IEEE80211AX
+
+static u8 find_bit_offset(u8 val)
+{
+       u8 res = 0;
+
+       for (; val; val >>= 1) {
+               if (val & 1)
+                       break;
+               res++;
+       }
+
+       return res;
+}
+
+
 static u8 set_he_cap(int val, u8 mask)
 {
-       return (u8) (mask & (val << ffs(mask)));
+       return (u8) (mask & (val << find_bit_offset(mask)));
 }
+
 #endif /* CONFIG_IEEE80211AX */