linux-kernel - [PATCH v2 2/2] staging: media: tegra-video: fix device

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Date:   Wed,  2 Nov 2022 12:01:02 +0100
From:   luca.ceresoli@...tlin.com
To:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Sowjanya Komatineni <skomatineni@...dia.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Dmitry Osipenko <digetx@...il.com>
Cc:     Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        linux-media@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Luca Ceresoli <luca.ceresoli@...tlin.com>,
        stable@...r.kernel.org
Subject: [PATCH v2 2/2] staging: media: tegra-video: fix device_node use after free

From: Luca Ceresoli <luca.ceresoli@...tlin.com>

At probe time this code path is followed:

 * tegra_csi_init
   * tegra_csi_channels_alloc
     * for_each_child_of_node(node, channel) -- iterates over channels
       * automatically gets 'channel'
         * tegra_csi_channel_alloc()
           * saves into chan->of_node a pointer to the channel OF node
       * automatically gets and puts 'channel'
       * now the node saved in chan->of_node has refcount 0, can disappear
   * tegra_csi_channels_init
     * iterates over channels
       * tegra_csi_channel_init -- uses chan->of_node

After that, chan->of_node keeps storing the node until the device is
removed.

of_node_get() the node and of_node_put() it during teardown to avoid any
risk.

Fixes: 1ebaeb09830f ("media: tegra-video: Add support for external sensor capture")
Cc: stable@...r.kernel.org
Cc: Sowjanya Komatineni <skomatineni@...dia.com>
Signed-off-by: Luca Ceresoli <luca.ceresoli@...tlin.com>

---

No changes in v2.
---
 drivers/staging/media/tegra-video/csi.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/staging/media/tegra-video/csi.c b/drivers/staging/media/tegra-video/csi.c
index 6b59ef55c525..426e653bd55d 100644
--- a/drivers/staging/media/tegra-video/csi.c
+++ b/drivers/staging/media/tegra-video/csi.c
@@ -433,7 +433,7 @@ static int tegra_csi_channel_alloc(struct tegra_csi *csi,
 	for (i = 0; i < chan->numgangports; i++)
 		chan->csi_port_nums[i] = port_num + i * CSI_PORTS_PER_BRICK;
 
-	chan->of_node = node;
+	chan->of_node = of_node_get(node);
 	chan->numpads = num_pads;
 	if (num_pads & 0x2) {
 		chan->pads[0].flags = MEDIA_PAD_FL_SINK;
@@ -641,6 +641,7 @@ static void tegra_csi_channels_cleanup(struct tegra_csi *csi)
 			media_entity_cleanup(&subdev->entity);
 		}
 
+		of_node_put(chan->of_node);
 		list_del(&chan->list);
 		kfree(chan);
 	}
-- 
2.34.1