[PATCH] mac80211: fix use-after-free in chanctx code

[Johannes Berg <johannes@sipsolutions.net>]

From: Johannes Berg <johannes.berg@intel.com>

In ieee80211_vif_use_reserved_context(), when we have an
old context and the new context's replace_state is set to
IEEE80211_CHANCTX_REPLACE_NONE, we free the old context
in ieee80211_vif_use_reserved_reassign(). Therefore, we
cannot check the old_ctx anymore, so we should set it to
NULL after this point.

However, since the new_ctx replace state is clearly not
IEEE80211_CHANCTX_REPLACES_OTHER, we're not going to do
anything else in this function and can just return to
avoid accessing the freed old_ctx.

Cc: stable@vger.kernel.org
Fixes: 5bcae31d9cb1 ("mac80211: implement multi-vif in-place reservations")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
 net/mac80211/chan.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/net/mac80211/chan.c b/net/mac80211/chan.c
index 7b249264af09..5d8b49f20198 100644
--- a/net/mac80211/chan.c
+++ b/net/mac80211/chan.c
@@ -1750,12 +1750,9 @@ int ieee80211_vif_use_reserved_context(struct ieee80211_sub_if_data *sdata)
 
 	if (new_ctx->replace_state == IEEE80211_CHANCTX_REPLACE_NONE) {
 		if (old_ctx)
-			err = ieee80211_vif_use_reserved_reassign(sdata);
-		else
-			err = ieee80211_vif_use_reserved_assign(sdata);
+			return ieee80211_vif_use_reserved_reassign(sdata);
 
-		if (err)
-			return err;
+		return ieee80211_vif_use_reserved_assign(sdata);
 	}
 
 	/*
-- 
2.36.1