Patch "mac80211: avoid excessive stack usage in sta_info" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

mac80211: avoid excessive stack usage in sta_info

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mac80211-avoid-excessive-stack-usage-in-sta_info.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Arnd Bergmann <[email protected]>
Date: Tue, 26 Jan 2016 23:05:31 +0100
Subject: mac80211: avoid excessive stack usage in sta_info

From: Arnd Bergmann <[email protected]>

commit 0ef049dc1167fe834d0ad5d63f89eddc5c70f6e4 upstream.

When CONFIG_OPTIMIZE_INLINING is set, the sta_info_insert_finish function consumes more stack than normally, exceeding the 1024 byte limit on ARM:

net/mac80211/sta_info.c: In function 'sta_info_insert_finish':
net/mac80211/sta_info.c:561:1: error: the frame size of 1080 bytes is larger than 1024 bytes [-Werror=frame-larger-than=]

It turns out that there are two functions that put a 'struct station_info' on the stack: __sta_info_destroy_part2 and sta_info_insert_finish, and this structure alone requires up to 792 bytes.

Hoping that both are called rarely enough, this replaces the on-stack structure with a dynamic allocation, which unfortunately requires some suboptimal error handling for out-of-memory.

The __sta_info_destroy_part2 function is actually affected by the stack usage twice because it calls cfg80211_del_sta_sinfo(), which has another instance of struct station_info on its stack.

---
 net/mac80211/sta_info.c |   24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

@@ -484,11 +484,17 @@ static int sta_info_insert_finish(struct
 {
 	struct ieee80211_local *local = sta->local;
 	struct ieee80211_sub_if_data *sdata = sta->sdata;
-	struct station_info sinfo;
+	struct station_info *sinfo;
 	int err = 0;
 
 	lockdep_assert_held(&local->sta_mtx);
 
+	sinfo = kzalloc(sizeof(struct station_info), GFP_KERNEL);
+	if (!sinfo) {
+		err = -ENOMEM;
+		goto out_err;
+	}
+
 	/* check if STA exists already */
 	if (sta_info_get_bss(sdata, sta->sta.addr)) {
 		err = -EEXIST;

@@ -522,10 +528,9 @@ static int sta_info_insert_finish(struct
 	ieee80211_sta_debugfs_add(sta);
 	rate_control_add_sta_debugfs(sta);
 
-	memset(&sinfo, 0, sizeof(sinfo));
-	sinfo.filled = 0;
-	sinfo.generation = local->sta_generation;
-	cfg80211_new_sta(sdata->dev, sta->sta.addr, &sinfo, GFP_KERNEL);
+	sinfo->generation = local->sta_generation;
+	cfg80211_new_sta(sdata->dev, sta->sta.addr, sinfo, GFP_KERNEL);
+	kfree(sinfo);
 
 	sta_dbg(sdata, "Inserted STA %pM\n", sta->sta.addr);
 

@@ -885,7 +890,7 @@ static void __sta_info_destroy_part2(str
 {
 	struct ieee80211_local *local = sta->local;
 	struct ieee80211_sub_if_data *sdata = sta->sdata;
-	struct station_info sinfo = {};
+	struct station_info *sinfo;
 	int ret;
 
 	/*

@@ -923,8 +928,11 @@ static void __sta_info_destroy_part2(str
 
 	sta_dbg(sdata, "Removed STA %pM\n", sta->sta.addr);
 
-	sta_set_sinfo(sta, &sinfo);
-	cfg80211_del_sta_sinfo(sdata->dev, sta->sta.addr, &sinfo, GFP_KERNEL);
+	sinfo = kzalloc(sizeof(*sinfo), GFP_KERNEL);
+	if (sinfo)
+		sta_set_sinfo(sta, sinfo);
+	cfg80211_del_sta_sinfo(sdata->dev, sta->sta.addr, sinfo, GFP_KERNEL);
+	kfree(sinfo);
 
 	rate_control_remove_sta_debugfs(sta);
 	ieee80211_sta_debugfs_remove(sta);

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/mac80211-avoid-excessive-stack-usage-in-sta_info.patch queue-4.4/farsync-fix-off-by-one-bug-in-fst_add_one.patch queue-4.4/pcmcia-db1xxx_ss-fix-last-irq_to_gpio-user.patch queue-4.4/ath9k-fix-buffer-overrun-for-ar9287.patch queue-4.4/iio-st_magn-always-define-st_magn_trigger_set_state.patch queue-4.4/hwmon-max1111-return-enodev-from-max1111_read_channel-if-not-instantiated.patch queue-4.4/mlx4-add-missing-braces-in-verify_qp_parameters.patch