netdev - [PATCH v2] rtw88: Fix out-of-bounds write

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Date:   Fri, 16 Jul 2021 17:53:11 +0200
From:   Len Baker <len.baker@....com>
To:     Yan-Hsuan Chuang <tony0620emma@...il.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     Len Baker <len.baker@....com>,
        Stanislaw Gruszka <sgruszka@...hat.com>,
        Brian Norris <briannorris@...omium.org>,
        Pkshih <pkshih@...ltek.com>, linux-wireless@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: [PATCH v2] rtw88: Fix out-of-bounds write

In the rtw_pci_init_rx_ring function the "if (len > TRX_BD_IDX_MASK)"
statement guarantees that len is less than or equal to GENMASK(11, 0) or
in other words that len is less than or equal to 4095. However the
rx_ring->buf has a size of RTK_MAX_RX_DESC_NUM (defined as 512). This
way it is possible an out-of-bounds write in the for statement due to
the i variable can exceed the rx_ring->buff size.

However, this overflow never happens due to the rtw_pci_init_rx_ring is
only ever called with a fixed constant of RTK_MAX_RX_DESC_NUM. But it is
better to be defensive in this case and add a new check to avoid
overflows if this function is called in a future with a value greater
than 512.

Cc: stable@...r.kernel.org
Addresses-Coverity-ID: 1461515 ("Out-of-bounds write")
Fixes: e3037485c68ec ("rtw88: new Realtek 802.11ac driver")
Signed-off-by: Len Baker <len.baker@....com>
---
Changelog v1 -> v2
- Remove the macro ARRAY_SIZE from the for loop (Pkshih, Brian Norris).
- Add a new check for the len variable (Pkshih, Brian Norris).

 drivers/net/wireless/realtek/rtw88/pci.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/net/wireless/realtek/rtw88/pci.c b/drivers/net/wireless/realtek/rtw88/pci.c
index e7d17ab8f113..53dc90276693 100644
--- a/drivers/net/wireless/realtek/rtw88/pci.c
+++ b/drivers/net/wireless/realtek/rtw88/pci.c
@@ -273,6 +273,11 @@ static int rtw_pci_init_rx_ring(struct rtw_dev *rtwdev,
 		return -EINVAL;
 	}

+	if (len > ARRAY_SIZE(rx_ring->buf)) {
+		rtw_err(rtwdev, "len %d exceeds maximum RX ring buffer\n", len);
+		return -EINVAL;
+	}
+
 	head = dma_alloc_coherent(&pdev->dev, ring_sz, &dma, GFP_KERNEL);
 	if (!head) {
 		rtw_err(rtwdev, "failed to allocate rx ring\n");
--
2.25.1