[PATCH 6.19 163/220] wifi: mac80211: always free skb on ieee80211_tx_prepare_skb() failure

Greg Kroah-Hartman
2026-03-23T13:57:53Z

From: Felix Fietkau <nbd@nbd.name>

[ Upstream commit d5ad6ab61cbd89afdb60881f6274f74328af3ee9 ]

ieee80211_tx_prepare_skb() has three error paths, but only two of them
free the skb. The first error path (ieee80211_tx_prepare() returning
TX_DROP) does not free it, while invoke_tx_handlers() failure and the
fragmentation check both do.

Add kfree_skb() to the first error path so all three are consistent,
and remove the now-redundant frees in callers (ath9k, mt76,
mac80211_hwsim) to avoid double-free.

Document the skb ownership guarantee in the function's kdoc.

Signed-off-by: Felix Fietkau <nbd@nbd.name>
Link: https://patch.msgid.link/20260314065455.2462900-1-nbd@nbd.name
Fixes: 06be6b149f7e ("mac80211: add ieee80211_tx_prepare_skb() helper function")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/net/wireless/ath/ath9k/channel.c | 6 ++----
drivers/net/wireless/mediatek/mt76/scan.c | 4 +---
drivers/net/wireless/virtual/mac80211_hwsim.c | 1 -
include/net/mac80211.h | 4 +++-
net/mac80211/tx.c | 4 +++-
5 files changed, 9 insertions(+), 10 deletions(-)

diff --git a/drivers/net/wireless/ath/ath9k/channel.c b/drivers/net/wireless/ath/ath9k/channel.c
index 121e51ce1bc0e..8b27d8cc086ab 100644
--- a/drivers/net/wireless/ath/ath9k/channel.c
+++ b/drivers/net/wireless/ath/ath9k/channel.c
@@ -1006,7 +1006,7 @@ static void ath_scan_send_probe(struct ath_softc *sc,
skb_set_queue_mapping(skb, IEEE80211_AC_VO);

if (!ieee80211_tx_prepare_skb(sc->hw, vif, skb, band, NULL))
- goto error;
+ return;

txctl.txq = sc->tx.txq_map[IEEE80211_AC_VO];
if (ath_tx_start(sc->hw, skb, &txctl))
@@ -1119,10 +1119,8 @@ ath_chanctx_send_vif_ps_frame(struct ath_softc *sc, struct ath_vif *avp,

skb->priority = 7;
skb_set_queue_mapping(skb, IEEE80211_AC_VO);
- if (!ieee80211_tx_prepare_skb(sc->hw, vif, skb, band, &sta)) {
- dev_kfree_skb_any(skb);
+ if (!ieee80211_tx_prepare_skb(sc->hw, vif, skb, band, &sta))
return false;
- }
break;
default:
return false;
diff --git a/drivers/net/wireless/mediatek/mt76/scan.c b/drivers/net/wireless/mediatek/mt76/scan.c
index ff9176cdee3de..63b0447e55c15 100644
--- a/drivers/net/wireless/mediatek/mt76/scan.c
+++ b/drivers/net/wireless/mediatek/mt76/scan.c
@@ -63,10 +63,8 @@ mt76_scan_send_probe(struct mt76_dev *dev, struct cfg80211_ssid *ssid)

rcu_read_lock();

- if (!ieee80211_tx_prepare_skb(phy->hw, vif, skb, band, NULL)) {
- ieee80211_free_txskb(phy->hw, skb);
+ if (!ieee80211_tx_prepare_skb(phy->hw, vif, skb, band, NULL))
goto out;
- }

info = IEEE80211_SKB_CB(skb);
if (req->no_cck)
diff --git a/drivers/net/wireless/virtual/mac80211_hwsim.c b/drivers/net/wireless/virtual/mac80211_hwsim.c
index 79cc63272134d..cfbd0c50be1c9 100644
--- a/drivers/net/wireless/virtual/mac80211_hwsim.c
+++ b/drivers/net/wireless/virtual/mac80211_hwsim.c
@@ -3021,7 +3021,6 @@ static void hw_scan_work(struct work_struct *work)
hwsim->tmp_chan->band,
NULL)) {
rcu_read_unlock();
- kfree_skb(probe);
continue;
}

diff --git a/include/net/mac80211.h b/include/net/mac80211.h
index c2e49542626c8..706f87c6d905a 100644
--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -7291,7 +7291,9 @@ void ieee80211_report_wowlan_wakeup(struct ieee80211_vif *vif,
* @band: the band to transmit on
* @sta: optional pointer to get the station to send the frame to
*
- * Return: %true if the skb was prepared, %false otherwise
+ * Return: %true if the skb was prepared, %false otherwise.
+ * On failure, the skb is freed by this function; callers must not
+ * free it again.
*
* Note: must be called under RCU lock
*/
diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index 1b55e83404135..0692fbb6c489e 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -1898,8 +1898,10 @@ bool ieee80211_tx_prepare_skb(struct ieee80211_hw *hw,
struct ieee80211_tx_data tx;
struct sk_buff *skb2;

- if (ieee80211_tx_prepare(sdata, &tx, NULL, skb) == TX_DROP)
+ if (ieee80211_tx_prepare(sdata, &tx, NULL, skb) == TX_DROP) {
+ kfree_skb(skb);
return false;
+ }

info->band = band;
info->control.vif = vif;
--
2.51.0