[PATCH v2 3/7] net: ks8851_mll: do not read past the receive buffer

[Sascha Hauer]

the hardware may report a packet longer than our receive buffer. Instead
of reading past the receive buffer, discard too long packets.

Signed-off-by: Sascha Hauer <s.ha...@pengutronix.de>
---
 drivers/net/ks8851_mll.c | 36 ++++++++++++++++++++++++++++++------
 1 file changed, 30 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ks8851_mll.c b/drivers/net/ks8851_mll.c
index 2120657bd9..936191597a 100644
--- a/drivers/net/ks8851_mll.c
+++ b/drivers/net/ks8851_mll.c
@@ -420,6 +420,23 @@ static inline void ks_inblk(struct ks_net *ks, u16 *wptr, 
u32 len)
                *wptr++ = (u16)readw(ks->hw_addr);
 }
 
+/**
+ * ks_discardblk - read a block of data from QMU discarding the data
+ * @ks: The chip state
+ * @len: length in byte to read
+ *
+ * This discards a block of data, used when a packet is longer than our receive
+ * buffer. I don't know if it is necessary to discard the data like this, but
+ * it is the easy way out to fix the behaviour with too large packets without
+ * risking regressions.
+ */
+static inline void ks_discardblk(struct ks_net *ks, u32 len)
+{
+       len >>= 1;
+       while (len--)
+               (void)readw(ks->hw_addr);
+}
+
 /**
  * ks_outblk - write data to QMU.
  * @ks: The chip information
@@ -676,16 +693,23 @@ static int ks8851_rx_frame(struct ks_net *ks)
 
        tmp_rxqcr = ks_rdreg16(ks, KS_RXQCR);
        ks_wrreg16(ks, KS_RXQCR, tmp_rxqcr | RXQCR_SDA);
-       /* read 2 bytes for dummy, 2 for status, 2 for len*/
-       ks_inblk(ks, ks->rx_buf, 2 + 2 + 2);
-       ks_inblk(ks, ks->rx_buf, ALIGN(RxLen, 4));
+       if (RxLen <= PKTSIZE) {
+               /* read 2 bytes for dummy, 2 for status, 2 for len*/
+               ks_inblk(ks, ks->rx_buf, 2 + 2 + 2);
+               ks_inblk(ks, ks->rx_buf, ALIGN(RxLen, 4));
+       } else {
+               ks_discardblk(ks, 2 + 2 + 2 + ALIGN(RxLen, 4));
+       }
+
        ks_wrreg16(ks, KS_RXQCR, tmp_rxqcr);
 
        if (RxStatus & RXFSHR_RXFV) {
                /* Pass to upper layer */
-               dev_dbg(dev, "passing packet to upper layer\n\n");
-               net_receive(&ks->edev, ks->rx_buf, RxLen);
-               return RxLen;
+               if (RxLen <= PKTSIZE) {
+                       dev_dbg(dev, "passing packet to upper layer\n\n");
+                       net_receive(&ks->edev, ks->rx_buf, RxLen);
+               }
+               return;
        } else if (RxStatus & RXFSHR_ERR) {
                dev_err(dev, "RxStatus error 0x%04x\n", RxStatus & RXFSHR_ERR);
                if (RxStatus & RXFSHR_RXICMPFCS)
-- 
2.39.2