The problem with PSM when a hidden SSID was used was originally
reported by Juuso Oikarinen.
- When generally scanning, the AP is getting a bss entry with
a zero SSID.
- When associationg, a probe-req is sent to the AP with the SSID,
and as a result a probe-responseis received with the hidden
SSID in place. As a consequence, a second bss entry is created
for the AP, now with the real SSID.
- After association, mac80211 executes ieee80211_recalc_ps(),
but does not switch to powersave because the beacon-ies are missing.
As result, the STA does not ever enter PSM.
The patch merges in beacon ies of hidden bss from beacon to the probe
response, creating a consistant set of ies in place.
Patch is depended on "cfg80211: fix cmp_ies" made by Johannes.
Signed-off-by: Dmitry Tarnyagin <dmitry.tarnyagin@xxxxxxxxxxxxxx>
---
net/wireless/scan.c | 117 +++++++++++++++++++++++++++++++++++++++++++++++++-
1 files changed, 114 insertions(+), 3 deletions(-)
diff --git a/net/wireless/scan.c b/net/wireless/scan.c
index 2ab0aba..87d1432 100644
--- a/net/wireless/scan.c
+++ b/net/wireless/scan.c
@@ -328,8 +328,8 @@ static bool is_mesh(struct cfg80211_bss *a,
sizeof(struct ieee80211_meshconf_ie) - 2) == 0;
}
-static int cmp_bss(struct cfg80211_bss *a,
- struct cfg80211_bss *b)
+static int cmp_bss_core(struct cfg80211_bss *a,
+ struct cfg80211_bss *b)
{
int r;
@@ -351,7 +351,15 @@ static int cmp_bss(struct cfg80211_bss *a,
b->len_information_elements);
}
- r = memcmp(a->bssid, b->bssid, ETH_ALEN);
+ return memcmp(a->bssid, b->bssid, ETH_ALEN);
+}
+
+static int cmp_bss(struct cfg80211_bss *a,
+ struct cfg80211_bss *b)
+{
+ int r;
+
+ r = cmp_bss_core(a, b);
if (r)
return r;
@@ -362,6 +370,52 @@ static int cmp_bss(struct cfg80211_bss *a,
b->len_information_elements);
}
+static int cmp_hidden_bss(struct cfg80211_bss *a,
+ struct cfg80211_bss *b)
+{
+ const u8 *ie1;
+ const u8 *ie2;
+ int i;
+ int r;
+
+ r = cmp_bss_core(a, b);
+ if (r)
+ return r;
+
+ ie1 = cfg80211_find_ie(WLAN_EID_SSID,
+ a->information_elements,
+ a->len_information_elements);
+ ie2 = cfg80211_find_ie(WLAN_EID_SSID,
+ b->information_elements,
+ b->len_information_elements);
+
+ /* Key comparator must use same algorithm in any rb-tree
+ * search function (order is important), otherwise ordering
+ * of items in the tree is broken and search gives incorrect
+ * results. This code uses same order as cmp_ies() does. */
+
+ /* sort missing IE before (left of) present IE */
+ if (!ie1)
+ return -1;
+ if (!ie2)
+ return 1;
+
+ /* zero-size SSID is used as an indication of the hidden bss */
+ if (!ie2[1])
+ return 0;
+
+ /* sort by length first, then by contents */
+ if (ie1[1] != ie2[1])
+ return ie2[1] - ie1[1];
+
+ /* zeroed SSID ie is another indication of a hidden bss */
+ for (i = 0; i < ie2[1]; i++)
+ if (ie2[i + 2])
+ return -1;
+
+ return 0;
+}
+
struct cfg80211_bss *cfg80211_get_bss(struct wiphy *wiphy,
struct ieee80211_channel *channel,
const u8 *bssid,
@@ -478,6 +532,48 @@ rb_find_bss(struct cfg80211_registered_device *dev,
}
static struct cfg80211_internal_bss *
+rb_find_hidden_bss(struct cfg80211_registered_device *dev,
+ struct cfg80211_internal_bss *res)
+{
+ struct rb_node *n = dev->bss_tree.rb_node;
+ struct cfg80211_internal_bss *bss;
+ int r;
+
+ while (n) {
+ bss = rb_entry(n, struct cfg80211_internal_bss, rbn);
+ r = cmp_hidden_bss(&res->pub, &bss->pub);
+
+ if (r == 0)
+ return bss;
+ else if (r < 0)
+ n = n->rb_left;
+ else
+ n = n->rb_right;
+ }
+
+ return NULL;
+}
+
+static void
+copy_hidden_ies(struct cfg80211_internal_bss *res,
+ struct cfg80211_internal_bss *hidden)
+{
+ if (unlikely(res->pub.beacon_ies))
+ return;
+ if (WARN_ON(!hidden->pub.beacon_ies))
+ return;
+
+ res->pub.beacon_ies = kmalloc(hidden->pub.len_beacon_ies, GFP_ATOMIC);
+ if (unlikely(!res->pub.beacon_ies))
+ return;
+
+ res->beacon_ies_allocated = true;
+ res->pub.len_beacon_ies = hidden->pub.len_beacon_ies;
+ memcpy(res->pub.beacon_ies, hidden->pub.beacon_ies,
+ res->pub.len_beacon_ies);
+}
+
+static struct cfg80211_internal_bss *
cfg80211_bss_update(struct cfg80211_registered_device *dev,
struct cfg80211_internal_bss *res)
{
@@ -590,6 +686,21 @@ cfg80211_bss_update(struct cfg80211_registered_device *dev,
kref_put(&res->ref, bss_release);
} else {
+ struct cfg80211_internal_bss *hidden;
+
+ /* First check if the beacon is a probe response from
+ * a hidden bss. If so, copy beacon ies (with nullified
+ * ssid) into the probe response bss entry (with real ssid).
+ * It is required basically for PSM implementation
+ * (probe responses do not contain tim ie) */
+
+ /* TODO: The code is not trying to update existing probe
+ * response bss entries when beacon ies are
+ * getting changed. */
+ hidden = rb_find_hidden_bss(dev, res);
+ if (hidden)
+ copy_hidden_ies(res, hidden);
+
/* this "consumes" the reference */
list_add_tail(&res->list, &dev->bss_list);
rb_insert_bss(dev, res);
--
With best regards,
Dmitry Tarnyagin
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