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From:   Sasha Levin <sashal@kernel.org>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc:     Aaro Koskinen <aaro.koskinen@nokia.com>,
        "David S . Miller" <davem@davemloft.net>,
        Sasha Levin <sashal@kernel.org>, netdev@vger.kernel.org
Subject: [PATCH AUTOSEL 5.0 31/66] net: stmmac: fix dropping of multi-descriptor RX frames
Date:   Wed, 24 Apr 2019 10:33:05 -0400
Message-Id: <20190424143341.27665-31-sashal@kernel.org>
In-Reply-To: <20190424143341.27665-1-sashal@kernel.org>
References: <20190424143341.27665-1-sashal@kernel.org>
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From: Aaro Koskinen <aaro.koskinen@nokia.com>

[ Upstream commit 8ac0c24fe1c256af6644caf3d311029440ec2fbd ]

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>
Signed-off-by: Sasha Levin (Microsoft) <sashal@kernel.org>
---
 drivers/net/ethernet/stmicro/stmmac/enh_desc.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/net/ethernet/stmicro/stmmac/enh_desc.c b/drivers/net/ethernet/stmicro/stmmac/enh_desc.c
index c42ef6c729c0..5202d6ad7919 100644
--- 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++;
-- 
2.19.1