[PATCH] net: sparx5/lan969x: do not read past skb->len when injecting a frame

[Daniel Machon]

sparx5_inject() writes the frame to the injection FIFO one 32-bit word
at a time, and pads frames shorter than 60 bytes with zero words.

Before this patch, the last word is loaded whole even when skb->len is
not a multiple of four, so 1 to 3 bytes past the end of the frame are
read. For a frame shorter than 60 bytes those bytes are also
transmitted, as VLD_BYTES marks the whole last word valid and the
padding starts at the next word.

Write the trailing bytes from a zeroed word. The number of words written
and VLD_BYTES are unchanged.

Found by an AI code review agent, and reproduced on lan969x and sparx5
with register injection: bytes 57 to 59 of a 57 byte frame were not
zero. With the fix they are zero, and traffic still passes on both
chips.

Fixes: f3cad2611a77 ("net: sparx5: add hostmode with phylink support")
Signed-off-by: Daniel Machon <daniel.machon@xxxxxxxxxxxxx>
---
 drivers/net/ethernet/microchip/sparx5/sparx5_packet.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/microchip/sparx5/sparx5_packet.c b/drivers/net/ethernet/microchip/sparx5/sparx5_packet.c
index f713656f1fae..14c9ae673e35 100644
--- a/drivers/net/ethernet/microchip/sparx5/sparx5_packet.c
+++ b/drivers/net/ethernet/microchip/sparx5/sparx5_packet.c
@@ -169,8 +169,8 @@ static int sparx5_inject(struct sparx5 *sparx5,
 			 struct sk_buff *skb,
 			 struct net_device *ndev)
 {
+	u32 val, w, count, last;
 	int grp = INJ_QUEUE;
-	u32 val, w, count;
 	u8 *buf;
 
 	val = spx5_rd(sparx5, QS_INJ_STATUS);
@@ -189,14 +189,23 @@ static int sparx5_inject(struct sparx5 *sparx5,
 	for (w = 0; w < IFH_LEN; w++)
 		spx5_wr(ifh[w], sparx5, QS_INJ_WR(grp));
 
-	/* Write words, round up */
-	count = DIV_ROUND_UP(skb->len, 4);
+	/* Write the whole words of the frame */
+	count = skb->len / 4;
 	buf = skb->data;
 	for (w = 0; w < count; w++, buf += 4) {
 		val = get_unaligned((const u32 *)buf);
 		spx5_wr(val, sparx5, QS_INJ_WR(grp));
 	}
 
+	/* Write the last 1 to 3 bytes, zero padded to a whole word */
+	last = skb->len % 4;
+	if (last) {
+		val = 0;
+		memcpy(&val, buf, last);
+		spx5_wr(val, sparx5, QS_INJ_WR(grp));
+		w++;
+	}
+
 	/* Add padding */
 	while (w < (60 / 4)) {
 		spx5_wr(0, sparx5, QS_INJ_WR(grp));

---
base-commit: d06ae66516e1aaf023808912af6292aef09d46c3
change-id: 20261020-sparx5-inject-tail-bytes-e81cffc5b065

Best regards,
-- 
Daniel Machon <daniel.machon@xxxxxxxxxxxxx>