net: stmmac: fix dropping of multi-descriptor RX frames

Packets without the last descriptor set should be dropped early. If we
receive a frame larger than the DMA buffer, the HW will continue using the
next descriptor. Driver mistakes these as individual frames, and sometimes
a truncated frame (without the LD set) may look like a valid packet.

This fixes a strange issue where the system replies to 4098-byte ping
although the MTU/DMA buffer size is set to 4096, and yet at the same
time it's logging an oversized packet.

Signed-off-by: Aaro Koskinen <aaro.koskinen@nokia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/ethernet/stmicro/stmmac/enh_desc.c b/drivers/net/ethernet/stmicro/stmmac/enh_desc.c
index c42ef6c729c0847ac404fa34b888409cf8a502d5..5202d6ad79194b0ed9134a7905d0aaa4309c6822 100644 (file)
--- a/drivers/net/ethernet/stmicro/stmmac/enh_desc.c
+++ b/drivers/net/ethernet/stmicro/stmmac/enh_desc.c
@@ -201,6 +201,11 @@ static int enh_desc_get_rx_status(void *data, struct stmmac_extra_stats *x,
        if (unlikely(rdes0 & RDES0_OWN))
                return dma_own;
 
+       if (unlikely(!(rdes0 & RDES0_LAST_DESCRIPTOR))) {
+               stats->rx_length_errors++;
+               return discard_frame;
+       }
+
        if (unlikely(rdes0 & RDES0_ERROR_SUMMARY)) {
                if (unlikely(rdes0 & RDES0_DESCRIPTOR_ERROR)) {
                        x->rx_desc++;