[PATCH net-next v2 4/4] net: dsa: qca8k: bound the data of a management ack frame

[Stanislaw Pal <kuncy7@gmail.com>]

qca8k_rw_reg_ack_handler() answers a management read by copying the
data that follows the Ethernet header into mgmt_eth_data->data. It
trusts the frame for both the length and the layout: the length field
of the frame allows up to 32 bytes while the buffer holds 16, so a
frame announcing more than three registers writes past the buffer into
the fields that follow it in qca8k_priv; and qca_tag_rcv() made only
the 2 byte tag linear, so the copy reads skb->data without checking
that the frame has the bytes it announces. The handler runs for every
ack frame, whatever its sequence number.

Size the buffer to what a management frame can carry, and pull the
announced data into the linear area before reading it. A frame that
is too short is left unacknowledged, so the read fails and the caller
falls back to MDIO.

An LLM assistant (Claude, claude-fable-5-1) helped write the change
and this description; I reviewed both and built them with W=1 on
arm64. The management path was exercised on a QCA8337 behind an
IPQ5018 (GL.iNet GL-B3000) with tag_qca.

Fixes: 90386223f44e ("net: dsa: qca8k: add support for larger read/write size with mgmt Ethernet")
Signed-off-by: Stanislaw Pal <kuncy7@gmail.com>
---
 drivers/net/dsa/qca/qca8k-8xxx.c | 21 ++++++++++++++++-----
 drivers/net/dsa/qca/qca8k.h      |  3 ++-
 2 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/drivers/net/dsa/qca/qca8k-8xxx.c b/drivers/net/dsa/qca/qca8k-8xxx.c
index bc77dd45b6..01834e16a2 100644
--- a/drivers/net/dsa/qca/qca8k-8xxx.c
+++ b/drivers/net/dsa/qca/qca8k-8xxx.c
@@ -170,6 +170,7 @@ static void qca8k_rw_reg_ack_handler(struct dsa_switch *ds, struct sk_buff *skb)
 	struct qca8k_mgmt_eth_data *mgmt_eth_data;
 	struct qca8k_priv *priv = ds->priv;
 	struct qca_mgmt_ethhdr *mgmt_ethhdr;
+	int data_len = 0;
 	u32 command;
 	u8 len, cmd;
 	int i;
@@ -190,6 +191,17 @@ static void qca8k_rw_reg_ack_handler(struct dsa_switch *ds, struct sk_buff *skb)
 	/* We can ignore odd value, we always round up them in the alloc function. */
 	len *= sizeof(u16);
 
+	if (cmd == MDIO_READ && len > QCA_HDR_MGMT_DATA1_LEN)
+		data_len = min_t(int, QCA_HDR_MGMT_DATA2_LEN,
+				 len - QCA_HDR_MGMT_DATA1_LEN);
+
+	/* The tagger made only the tag linear. Leave a frame that is too
+	 * short for the data it announces unacknowledged: the read fails
+	 * and the caller falls back to MDIO.
+	 */
+	if (data_len && !pskb_may_pull(skb, data_len))
+		goto complete;
+
 	/* Make sure the seq match the requested packet */
 	if (get_unaligned_le32(&mgmt_ethhdr->seq) == mgmt_eth_data->seq)
 		mgmt_eth_data->ack = true;
@@ -199,13 +211,11 @@ static void qca8k_rw_reg_ack_handler(struct dsa_switch *ds, struct sk_buff *skb)
 
 		*val = get_unaligned_le32(&mgmt_ethhdr->mdio_data);
 
-		/* Get the rest of the 12 byte of data.
-		 * The read/write function will extract the requested data.
+		/* Get the rest of the data.
+		 * The read function extracts what it asked for.
 		 */
-		if (len > QCA_HDR_MGMT_DATA1_LEN) {
+		if (data_len) {
 			__le32 *data2 = (__le32 *)skb->data;
-			int data_len = min_t(int, QCA_HDR_MGMT_DATA2_LEN,
-					     len - QCA_HDR_MGMT_DATA1_LEN);
 
 			val++;
 
@@ -217,6 +227,7 @@ static void qca8k_rw_reg_ack_handler(struct dsa_switch *ds, struct sk_buff *skb)
 		}
 	}
 
+complete:
 	complete(&mgmt_eth_data->rw_done);
 }
 
diff --git a/drivers/net/dsa/qca/qca8k.h b/drivers/net/dsa/qca/qca8k.h
index 79754755f1..b7aa0d832e 100644
--- a/drivers/net/dsa/qca/qca8k.h
+++ b/drivers/net/dsa/qca/qca8k.h
@@ -396,7 +396,8 @@ struct qca8k_mgmt_eth_data {
 	struct mutex mutex; /* Enforce one mdio read/write at time */
 	bool ack;
 	u32 seq;
-	u32 data[4];
+	/* The data a management frame can carry */
+	u32 data[(QCA_HDR_MGMT_DATA1_LEN + QCA_HDR_MGMT_DATA2_LEN) / sizeof(u32)];
 };
 
 struct qca8k_mib_eth_data {
-- 
2.43.0