[PATCH] net: stmmac: fix memory corruption with large MTUs

From: Aaro Koskinen
Date: Mon Mar 18 2019 - 17:37:43 EST

From: Aaro Koskinen <aaro.koskinen@xxxxxxxxx>

When using 16K DMA buffers and ring mode, the DES3 refill is not working
correctly as the function is using a bogus pointer for checking the
private data. As a result stale pointers will remain in the RX descriptor
ring, so DMA will now likely overwrite/corrupt some already freed memory.

As simple reproducer, just receive some UDP traffic:

# ifconfig eth0 down; ifconfig eth0 mtu 9000; ifconfig eth0 up
# iperf3 -c -u -b 0 -R

If you didn't crash by now check the RX descriptors to find non-contiguous
RX buffers:

cat /sys/kernel/debug/stmmaceth/eth0/descriptors_status
1 [0x2be5020]: 0xa3220321 0x9ffc1ffc 0x72d70082 0x130e207e
2 [0x2be5040]: 0xa3220321 0x9ffc1ffc 0x72998082 0x1311a07e

A simple ping test will now report bad data:

# ping -s 8200
PING ( 8200(8228) bytes of data.
8208 bytes from icmp_seq=1 ttl=64 time=1.00 ms
wrong data byte #8144 should be 0xd0 but was 0x88

Fix the wrong pointer. Also we must refill DES3 only if the DMA buffer
size is 16K.

Fixes: 54139cf3bb33 ("net: stmmac: adding multiple buffers for rx")
Signed-off-by: Aaro Koskinen <aaro.koskinen@xxxxxxxxx>
drivers/net/ethernet/stmicro/stmmac/ring_mode.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/ring_mode.c b/drivers/net/ethernet/stmicro/stmmac/ring_mode.c
index f936166d8910..4d9bcb4d0378 100644
--- a/drivers/net/ethernet/stmicro/stmmac/ring_mode.c
+++ b/drivers/net/ethernet/stmicro/stmmac/ring_mode.c
@@ -113,10 +113,11 @@ static unsigned int is_jumbo_frm(int len, int enh_desc)

static void refill_desc3(void *priv_ptr, struct dma_desc *p)
- struct stmmac_priv *priv = (struct stmmac_priv *)priv_ptr;
+ struct stmmac_rx_queue *rx_q = priv_ptr;
+ struct stmmac_priv *priv = rx_q->priv_data;

/* Fill DES3 in case of RING mode */
- if (priv->dma_buf_sz >= BUF_SIZE_8KiB)
+ if (priv->dma_buf_sz == BUF_SIZE_16KiB)
p->des3 = cpu_to_le32(le32_to_cpu(p->des2) + BUF_SIZE_8KiB);