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Sun, 04 Jan 2026 16:27:00 -0800 (PST) From: Zac Bowling To: zbowling@gmail.com Cc: deren.wu@mediatek.com, kvalo@kernel.org, linux-kernel@vger.kernel.org, linux-mediatek@lists.infradead.org, linux-wireless@vger.kernel.org, lorenzo@kernel.org, nbd@nbd.name, ryder.lee@mediatek.com, sean.wang@mediatek.com Subject: [PATCH 10/17] wifi: mt76: mt792x: fix NULL pointer dereference in TX path Date: Sun, 4 Jan 2026 16:26:31 -0800 Message-ID: <20260105002638.668723-11-zbowling@gmail.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260105002638.668723-1-zbowling@gmail.com> References: <20260102200524.290779-1-zbowling@gmail.com> <20260105002638.668723-1-zbowling@gmail.com> Precedence: bulk X-Mailing-List: linux-wireless@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Add NULL pointer checks in mt792x_tx() to prevent kernel crashes when transmitting packets during MLO link removal. The function calls mt792x_sta_to_link() which can return NULL if the link is being removed, but the return value was dereferenced without checking. Similarly, the RCU-protected link_conf and link_sta pointers were used without NULL validation. This race can occur when: 1. A packet is queued for transmission 2. Concurrently, the link is being removed (mt7925_mac_link_sta_remove) 3. mt792x_sta_to_link() returns NULL for the removed link 4. Kernel crashes on wcid = &mlink->wcid dereference Example crash trace: BUG: kernel NULL pointer dereference RIP: mt792x_tx+0x... Call Trace: ieee80211_tx+0x... __ieee80211_subif_start_xmit+0x... Fix by: - Check mlink return value before dereferencing wcid - Check RCU-dereferenced conf and link_sta before use - Free the SKB and return early if any pointer is NULL This affects both MT7921 and MT7925 drivers as mt792x_core.c is shared. Fixes: c74df1c067f2 ("wifi: mt76: mt792x: introduce mt792x-lib module") Reported-by: Zac Bowling Signed-off-by: Zac Bowling --- drivers/net/wireless/mediatek/mt76/mt792x_core.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/drivers/net/wireless/mediatek/mt76/mt792x_core.c b/drivers/net/wireless/mediatek/mt76/mt792x_core.c index f2ed16feb6c1..9dc768aa8b9c 100644 --- a/drivers/net/wireless/mediatek/mt76/mt792x_core.c +++ b/drivers/net/wireless/mediatek/mt76/mt792x_core.c @@ -95,6 +95,8 @@ void mt792x_tx(struct ieee80211_hw *hw, struct ieee80211_tx_control *control, IEEE80211_TX_CTRL_MLO_LINK); sta = (struct mt792x_sta *)control->sta->drv_priv; mlink = mt792x_sta_to_link(sta, link_id); + if (!mlink) + goto free_skb; wcid = &mlink->wcid; } @@ -113,9 +115,12 @@ void mt792x_tx(struct ieee80211_hw *hw, struct ieee80211_tx_control *control, link_id = wcid->link_id; rcu_read_lock(); conf = rcu_dereference(vif->link_conf[link_id]); - memcpy(hdr->addr2, conf->addr, ETH_ALEN); - link_sta = rcu_dereference(control->sta->link[link_id]); + if (!conf || !link_sta) { + rcu_read_unlock(); + goto free_skb; + } + memcpy(hdr->addr2, conf->addr, ETH_ALEN); memcpy(hdr->addr1, link_sta->addr, ETH_ALEN); if (vif->type == NL80211_IFTYPE_STATION) @@ -136,6 +141,10 @@ void mt792x_tx(struct ieee80211_hw *hw, struct ieee80211_tx_control *control, } mt76_connac_pm_queue_skb(hw, &dev->pm, wcid, skb); + return; + +free_skb: + ieee80211_free_txskb(hw, skb); } EXPORT_SYMBOL_GPL(mt792x_tx); -- 2.51.0