linux-kernel - [PATCH] media: mtk-vcodec: Fix a NULL pointer dereference in mtk_vcodec_fw_scp

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Date:   Tue, 25 Jan 2022 01:07:31 +0800
From:   Zhou Qingyang <zhou1615@....edu>
To:     zhou1615@....edu
Cc:     kjlu@....edu, Tiffany Lin <tiffany.lin@...iatek.com>,
        Andrew-CT Chen <andrew-ct.chen@...iatek.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Alexandre Courbot <acourbot@...omium.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        linux-media@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH] media: mtk-vcodec: Fix a NULL pointer dereference in mtk_vcodec_fw_scp_init()

In mtk_vcodec_fw_scp_init(), devm_kzalloc() is assigned to fw and there is
a dereference of it right after that, which could lead to NULL pointer
dereference on failure of devm_kzalloc().

Fix this bug by adding a NULL check of fw.

This bug was found by a static analyzer.

Builds with 'make allyesconfig' show no new warnings,
and our static analyzer no longer warns about this code.

Fixes: 46233e91fa24 ("media: mtk-vcodec: move firmware implementations into their own files")
Signed-off-by: Zhou Qingyang <zhou1615@....edu>
---
The analysis employs differential checking to identify inconsistent 
security operations (e.g., checks or kfrees) between two code paths 
and confirms that the inconsistent operations are not recovered in the
current function or the callers, so they constitute bugs. 

Note that, as a bug found by static analysis, it can be a false
positive or hard to trigger. Multiple researchers have cross-reviewed
the bug.

 drivers/media/platform/mtk-vcodec/mtk_vcodec_fw_scp.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/media/platform/mtk-vcodec/mtk_vcodec_fw_scp.c b/drivers/media/platform/mtk-vcodec/mtk_vcodec_fw_scp.c
index d8e66b645bd8..aa36bee51d01 100644
--- a/drivers/media/platform/mtk-vcodec/mtk_vcodec_fw_scp.c
+++ b/drivers/media/platform/mtk-vcodec/mtk_vcodec_fw_scp.c
@@ -65,6 +65,9 @@ struct mtk_vcodec_fw *mtk_vcodec_fw_scp_init(struct mtk_vcodec_dev *dev)
 	}
 
 	fw = devm_kzalloc(&dev->plat_dev->dev, sizeof(*fw), GFP_KERNEL);
+	if (!fw)
+		return ERR_PTR(-ENOMEM);
+
 	fw->type = SCP;
 	fw->ops = &mtk_vcodec_rproc_msg;
 	fw->scp = scp;
-- 
2.25.1