[PATCH 33/58] iwlwifi: dvm: fix calling ieee80211_chswitch_done() with NULL

[Luis Henriques <luis.henriques@canonical.com>]

3.5.7.21 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Stanislaw Gruszka <sgruszka@redhat.com>

commit 9186a1fd9ed190739423db84bc344d258ef3e3d7 upstream.

If channel switch is pending and we remove interface we can
crash like showed below due to passing NULL vif to mac80211:

BUG: unable to handle kernel paging request at fffffffffffff8cc
IP: [<ffffffff8130924d>] strnlen+0xd/0x40
Call Trace:
 [<ffffffff8130ad2e>] string.isra.3+0x3e/0xd0
 [<ffffffff8130bf99>] vsnprintf+0x219/0x640
 [<ffffffff8130c481>] vscnprintf+0x11/0x30
 [<ffffffff81061585>] vprintk_emit+0x115/0x4f0
 [<ffffffff81657bd5>] printk+0x61/0x63
 [<ffffffffa048987f>] ieee80211_chswitch_done+0xaf/0xd0 [mac80211]
 [<ffffffffa04e7b34>] iwl_chswitch_done+0x34/0x40 [iwldvm]
 [<ffffffffa04f83c3>] iwlagn_commit_rxon+0x2a3/0xdc0 [iwldvm]
 [<ffffffffa04ebc50>] ? iwlagn_set_rxon_chain+0x180/0x2c0 [iwldvm]
 [<ffffffffa04e5e76>] iwl_set_mode+0x36/0x40 [iwldvm]
 [<ffffffffa04e5f0d>] iwlagn_mac_remove_interface+0x8d/0x1b0 [iwldvm]
 [<ffffffffa0459b3d>] ieee80211_do_stop+0x29d/0x7f0 [mac80211]

This is because we nulify ctx->vif in iwlagn_mac_remove_interface()
before calling some other functions that teardown interface. To fix
just check ctx->vif on iwl_chswitch_done(). We should not call
ieee80211_chswitch_done() as channel switch works were already canceled
by mac80211 in ieee80211_do_stop() -> ieee80211_mgd_stop().

Resolve:
https://bugzilla.redhat.com/show_bug.cgi?id=979581

Reported-by: Lukasz Jagiello <jagiello.lukasz@gmail.com>
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
[ luis: backported to 3.5: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
 drivers/net/wireless/iwlwifi/iwl-mac80211.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wireless/iwlwifi/iwl-mac80211.c b/drivers/net/wireless/iwlwifi/iwl-mac80211.c
index 2c86c55..40bf6ad 100644
--- a/drivers/net/wireless/iwlwifi/iwl-mac80211.c
+++ b/drivers/net/wireless/iwlwifi/iwl-mac80211.c
@@ -958,7 +958,10 @@ void iwl_chswitch_done(struct iwl_priv *priv, bool is_success)
 	if (test_bit(STATUS_EXIT_PENDING, &priv->status))
 		return;
 
-	if (test_and_clear_bit(STATUS_CHANNEL_SWITCH_PENDING, &priv->status))
+	if (!test_and_clear_bit(STATUS_CHANNEL_SWITCH_PENDING, &priv->status))
+		return;
+
+	if (ctx->vif)
 		ieee80211_chswitch_done(ctx->vif, is_success);
 }
 
-- 
1.8.3.2