[PATCH net-next v3 1/2] net: stmmac: take ownership of saved RX state at poll entry

[Lorenzo Bianconi]

From: James Hilliard <james.hilliard1 at gmail.com>

When a saved partial packet completes with a poll budget of one, the
old loop can leave state_saved and state.skb pointing at an skb that
has already been delivered or freed. The next poll then reuses that
pointer, causing a use-after-free or double free.

Take the saved state at poll entry and clear the stored ownership
immediately. Save it again only if the packet remains incomplete,
including when the next descriptor is still DMA-owned. Release a
saved partial skb when the RX ring is destroyed.

Apply the same state handling to stmmac_rx_zc(), which also leaves
state_saved set when a saved frame finishes at the budget boundary.
That path saves only error and length bookkeeping, not an skb pointer.
Track whether a frame remains incomplete independently of the status
read from the next descriptor, so a DMA-owned descriptor does not erase
the continuation state.

Fixes: ec222003bd94 ("net: stmmac: Prepare to add Split Header support")
Fixes: bba2556efad6 ("net: stmmac: Enable RX via AF_XDP zero-copy")
Signed-off-by: James Hilliard <james.hilliard1 at gmail.com>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 54 +++++++++++++++--------
 1 file changed, 35 insertions(+), 19 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 0c381ae0d0ff..b2d20628ed21 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -2180,6 +2180,9 @@ static void __free_dma_rx_desc_resources(struct stmmac_priv *priv,
 	else
 		dma_free_rx_skbufs(priv, dma_conf, queue);
 
+	dev_kfree_skb_any(rx_q->state.skb);
+	rx_q->state.skb = NULL;
+	rx_q->state_saved = false;
 	rx_q->buf_alloc_num = 0;
 	rx_q->xsk_pool = NULL;
 
@@ -5581,12 +5584,12 @@ static int stmmac_rx_zc(struct stmmac_priv *priv, int limit, u32 queue)
 	unsigned int count = 0, error = 0, len = 0;
 	int dirty = stmmac_rx_dirty(priv, queue);
 	unsigned int next_entry = rx_q->cur_rx;
+	bool in_progress = rx_q->state_saved;
 	u32 rx_errors = 0, rx_dropped = 0;
 	unsigned int desc_size;
 	struct bpf_prog *prog;
 	bool failure = false;
 	int xdp_status = 0;
-	int status = 0;
 
 	if (netif_msg_rx_status(priv)) {
 		void *rx_head = stmmac_get_rx_desc(priv, rx_q, 0);
@@ -5597,23 +5600,25 @@ static int stmmac_rx_zc(struct stmmac_priv *priv, int limit, u32 queue)
 		stmmac_display_ring(priv, rx_head, priv->dma_conf.dma_rx_size, true,
 				    rx_q->dma_rx_phy, desc_size);
 	}
+
+	if (rx_q->state_saved) {
+		error = rx_q->state.error;
+		len = rx_q->state.len;
+		rx_q->state_saved = false;
+	}
+
 	while (count < limit) {
 		struct stmmac_rx_buffer *buf;
 		struct stmmac_xdp_buff *ctx;
 		unsigned int buf1_len = 0;
 		struct dma_desc *np, *p;
-		int entry;
+		int entry, status;
 		int res;
 
-		if (!count && rx_q->state_saved) {
-			error = rx_q->state.error;
-			len = rx_q->state.len;
-		} else {
-			rx_q->state_saved = false;
+		if (!in_progress) {
 			error = 0;
 			len = 0;
 		}
-
 read_again:
 		if (count >= limit)
 			break;
@@ -5652,6 +5657,8 @@ static int stmmac_rx_zc(struct stmmac_priv *priv, int limit, u32 queue)
 		if (!buf->xdp)
 			break;
 
+		in_progress = status & rx_not_ls;
+
 		if (priv->extend_desc)
 			stmmac_rx_extended_status(priv, &priv->xstats,
 						  rx_q->dma_erx + entry);
@@ -5724,7 +5731,7 @@ static int stmmac_rx_zc(struct stmmac_priv *priv, int limit, u32 queue)
 		count++;
 	}
 
-	if (status & rx_not_ls) {
+	if (in_progress) {
 		rx_q->state_saved = true;
 		rx_q->state.error = error;
 		rx_q->state.len = len;
@@ -5766,9 +5773,10 @@ static int stmmac_rx(struct stmmac_priv *priv, int limit, u32 queue)
 	struct stmmac_rx_queue *rx_q = &priv->dma_conf.rx_queue[queue];
 	struct stmmac_channel *ch = &priv->channel[queue];
 	unsigned int count = 0, error = 0, len = 0;
-	int status = 0, coe = priv->hw->rx_csum;
 	unsigned int next_entry = rx_q->cur_rx;
+	bool in_progress = rx_q->state_saved;
 	enum dma_data_direction dma_dir;
+	int coe = priv->hw->rx_csum;
 	unsigned int desc_size;
 	struct sk_buff *skb = NULL;
 	struct stmmac_xdp_buff ctx;
@@ -5788,25 +5796,28 @@ static int stmmac_rx(struct stmmac_priv *priv, int limit, u32 queue)
 		stmmac_display_ring(priv, rx_head, priv->dma_conf.dma_rx_size, true,
 				    rx_q->dma_rx_phy, desc_size);
 	}
+
+	if (rx_q->state_saved) {
+		skb = rx_q->state.skb;
+		error = rx_q->state.error;
+		len = rx_q->state.len;
+		rx_q->state.skb = NULL;
+		rx_q->state_saved = false;
+	}
+
 	while (count < limit) {
 		unsigned int buf1_len = 0, buf2_len = 0;
 		enum pkt_hash_types hash_type;
 		struct stmmac_rx_buffer *buf;
 		struct dma_desc *np, *p;
-		int entry;
+		int entry, status;
 		u32 hash;
 
-		if (!count && rx_q->state_saved) {
-			skb = rx_q->state.skb;
-			error = rx_q->state.error;
-			len = rx_q->state.len;
-		} else {
-			rx_q->state_saved = false;
+		if (!in_progress) {
 			skb = NULL;
 			error = 0;
 			len = 0;
 		}
-
 read_again:
 		if (count >= limit)
 			break;
@@ -5835,6 +5846,8 @@ static int stmmac_rx(struct stmmac_priv *priv, int limit, u32 queue)
 
 		prefetch(np);
 
+		in_progress = status & rx_not_ls;
+
 		if (priv->extend_desc)
 			stmmac_rx_extended_status(priv, &priv->xstats, rx_q->dma_erx + entry);
 		if (unlikely(status == discard_frame)) {
@@ -6019,7 +6032,7 @@ static int stmmac_rx(struct stmmac_priv *priv, int limit, u32 queue)
 		count++;
 	}
 
-	if (status & rx_not_ls || skb) {
+	if (in_progress || skb) {
 		rx_q->state_saved = true;
 		rx_q->state.skb = skb;
 		rx_q->state.error = error;
@@ -8339,6 +8352,9 @@ static void stmmac_reset_rx_queue(struct stmmac_priv *priv, u32 queue)
 {
 	struct stmmac_rx_queue *rx_q = &priv->dma_conf.rx_queue[queue];
 
+	dev_kfree_skb_any(rx_q->state.skb);
+	rx_q->state.skb = NULL;
+	rx_q->state_saved = false;
 	rx_q->cur_rx = 0;
 	rx_q->dirty_rx = 0;
 }

-- 
2.55.0