[PATCH v2] cfg80211: fix BSS comparison

[PATCH v2] cfg80211: fix BSS comparison

[Emmanuel Grumbach]

Since the BSS table is organized in a RB tree, the BSSs need to be
comparable. This means that we must define a < and > operator to
the BSS object.
compare_ethr_addr isn't enough since it returns only a binary value.

Since Felix's

cfg80211: use compare_ether_addr on MAC addresses instead of memcmp

    Because of the constant size and guaranteed 16 bit alignment, the inline
    compare_ether_addr function is much cheaper than calling memcmp.

    Signed-off-by: Felix Fietkau <nbd@openwrt.org>
    Signed-off-by: John W. Linville <linville@tuxdriver.com>

The BSS table is corrupted: rb_find_bss can't find the bss.
As a result BSSes are duplicated in the BSS table, and we get stuck
while probing an AP before associating (in STA mode).

Change-Id: I85928756f4328028230832c1565ece7f412f3843
CC: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
---
v2: add a comment to warn the next guy that will try to over optimize :-)
---
 net/wireless/scan.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/net/wireless/scan.c b/net/wireless/scan.c
index bd6a0ee..aa01335 100644
--- a/net/wireless/scan.c
+++ b/net/wireless/scan.c
@@ -378,7 +378,11 @@ static int cmp_bss_core(struct cfg80211_bss *a,
 			       b->len_information_elements);
 	}
 
-	return compare_ether_addr(a->bssid, b->bssid);
+	/*
+	 * we can't use compare_ether_addr here since we need a < > operator.
+	 * The binary return value of compare_ether_addr isn't enough
+	 */
+	return memcmp(a->bssid, b->bssid, sizeof(a->bssid));
 }
 
 static int cmp_bss(struct cfg80211_bss *a,
-- 
1.7.1

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Re: [PATCH v2] cfg80211: fix BSS comparison

[Felix Fietkau]

On 2012-04-30 9:23 AM, Emmanuel Grumbach wrote:
> Since the BSS table is organized in a RB tree, the BSSs need to be
> comparable. This means that we must define a < and > operator to
> the BSS object.
> compare_ethr_addr isn't enough since it returns only a binary value.
> 
> Since Felix's
> 
> cfg80211: use compare_ether_addr on MAC addresses instead of memcmp
> 
>     Because of the constant size and guaranteed 16 bit alignment, the inline
>     compare_ether_addr function is much cheaper than calling memcmp.
> 
>     Signed-off-by: Felix Fietkau <nbd@openwrt.org>
>     Signed-off-by: John W. Linville <linville@tuxdriver.com>
> 
> The BSS table is corrupted: rb_find_bss can't find the bss.
> As a result BSSes are duplicated in the BSS table, and we get stuck
> while probing an AP before associating (in STA mode).
> 
> Change-Id: I85928756f4328028230832c1565ece7f412f3843
> CC: Felix Fietkau <nbd@openwrt.org>
> Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Looks good, thanks for finding this.
Acked-by: Felix Fietkau <nbd@openwrt.org>