[PATCH net] net: phy: air_en8811h: refuse a firmware blob that is not a multiple of 4

The download loop streams the blob into the MCU as 32-bit words and
reads the last word past the end of a blob whose size is not a multiple
of four. The shipped blobs happen to be aligned, so the overread never
showed; a truncated or foreign file would carry up to three bytes of
whatever follows it into the MCU. Reject it before the first write
instead.

Fixes: 71e79430117d ("net: phy: air_en8811h: Add the Airoha EN8811H PHY driver")
Assisted-by: LLM
Signed-off-by: Aleksei Sviridkin <redacted>
---
 drivers/net/phy/air_en8811h.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/net/phy/air_en8811h.c b/drivers/net/phy/air_en8811h.c
index 0eeb7b9a4e26..34d2727e8222 100644
--- a/drivers/net/phy/air_en8811h.c
+++ b/drivers/net/phy/air_en8811h.c

@@ -312,6 +312,12 @@ static int air_write_buf(struct phy_device *phydev, u32 address,
 	int saved_page;
 	int ret = 0;
 
+	if (fw->size % 4) {
+		phydev_err(phydev, "firmware size %zu is not a multiple of 4\n",
+			   fw->size);
+		return -EINVAL;
+	}
+
 	saved_page = phy_select_page(phydev, AIR_PHY_PAGE_EXTENDED_4);
 
 	if (saved_page >= 0) {

-- 
2.53.0