linux-kernel - [PATCH] mmc: owl-mmc: Fix dma_chan refcnt leak in owl_mmc

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Date:   Sat, 25 Apr 2020 20:53:45 +0800
From:   Xiyu Yang <xiyuyang19@...an.edu.cn>
To:     Ulf Hansson <ulf.hansson@...aro.org>,
        Andreas Färber <afaerber@...e.de>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        linux-mmc@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Cc:     yuanxzhang@...an.edu.cn, kjlu@....edu,
        Xiyu Yang <xiyuyang19@...an.edu.cn>,
        Xin Tan <tanxin.ctf@...il.com>
Subject: [PATCH] mmc: owl-mmc: Fix dma_chan refcnt leak in owl_mmc_probe()

owl_mmc_probe() invokes dma_request_chan(), which returns a reference of
the specified dma_chan object to "owl_host->dma" with increased refcnt.

When owl_mmc_probe() encounters error, it calls mmc_free_host() to free
the "mmc" memory. Since "owl_host" comes from one of "mmc" fields, this
"free" behavior causes "owl_host" and "owl_host->dma" become invalid, so
the refcount for its field should be decreased to keep refcount balanced
before mmc_free_host() calls.

The reference counting issue happens in several exception handling paths
of owl_mmc_probe(). When those error scenarios occur such as failed to
request irq, the function forgets to decrease the refcnt increased by
dma_request_chan(), causing a refcnt leak.

Fix this issue by jumping to "err_put_dma" label when those error
scenarios occur.

Signed-off-by: Xiyu Yang <xiyuyang19@...an.edu.cn>
Signed-off-by: Xin Tan <tanxin.ctf@...il.com>
---
 drivers/mmc/host/owl-mmc.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/mmc/host/owl-mmc.c b/drivers/mmc/host/owl-mmc.c
index 01ffe51f413d..4dc72f5f32f5 100644
--- a/drivers/mmc/host/owl-mmc.c
+++ b/drivers/mmc/host/owl-mmc.c
@@ -635,7 +635,7 @@ static int owl_mmc_probe(struct platform_device *pdev)
 	owl_host->irq = platform_get_irq(pdev, 0);
 	if (owl_host->irq < 0) {
 		ret = -EINVAL;
-		goto err_free_host;
+		goto err_put_dma;
 	}

 	ret = devm_request_irq(&pdev->dev, owl_host->irq, owl_irq_handler,
@@ -643,19 +643,22 @@ static int owl_mmc_probe(struct platform_device *pdev)
 	if (ret) {
 		dev_err(&pdev->dev, "Failed to request irq %d\n",
 			owl_host->irq);
-		goto err_free_host;
+		goto err_put_dma;
 	}

 	ret = mmc_add_host(mmc);
 	if (ret) {
 		dev_err(&pdev->dev, "Failed to add host\n");
-		goto err_free_host;
+		goto err_put_dma;
 	}

 	dev_dbg(&pdev->dev, "Owl MMC Controller Initialized\n");

 	return 0;

+err_put_dma:
+	if (owl_host->dma)
+		dma_release_channel(owl_host->dma);
 err_free_host:
 	mmc_free_host(mmc);

-- 
2.7.4