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Date:   Mon, 18 Mar 2019 23:36:08 +0200
From:   Aaro Koskinen <>
To:     "David S. Miller" <>,
        Giuseppe Cavallaro <>,
        Alexandre Torgue <>,
        Jose Abreu <>,,
Cc:     Aaro Koskinen <>
Subject: [PATCH] net: stmmac: fix memory corruption with large MTUs

From: Aaro Koskinen <>

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 <>
 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);

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