linux-kernel - [PATCH V3] media: dvb-usb: pctv452e: move snd/rcv len check before kmalloc

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Message-ID: <tencent_7D8067C646C712F50668898DEEC9AEE48C06@qq.com>
Date: Mon,  3 Nov 2025 19:57:49 +0800
From: Edward Adam Davis <eadavis@...com>
To: hverkuil+cisco@...nel.org
Cc: eadavis@...com,
	linux-kernel@...r.kernel.org,
	linux-media@...r.kernel.org,
	mchehab@...nel.org,
	syzbot+480edd2cadb85ddb4bbe@...kaller.appspotmail.com,
	syzkaller-bugs@...glegroups.com
Subject: [PATCH V3] media: dvb-usb: pctv452e: move snd/rcv len check before kmalloc

syzbot reported a uninit-value in pctv452e_i2c_msg. [1]

When the snd_len or rcv_len check fails and jumps to failed, buf is
uninitialized, triggering the uninit-value issue.

Move the snd/rcv length check before kmalloc, and return -EINVAL directly
if the condition is met.

[1]
BUG: KMSAN: uninit-value in hex_string+0x681/0x740 lib/vsprintf.c:1220
 pctv452e_i2c_msg+0x82a/0x8f0 drivers/media/usb/dvb-usb/pctv452e.c:467
 pctv452e_i2c_xfer+0x2e6/0x4c0 drivers/media/usb/dvb-usb/pctv452e.c:502

Reported-by: syzbot+480edd2cadb85ddb4bbe@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=480edd2cadb85ddb4bbe
Signed-off-by: Edward Adam Davis <eadavis@...com>
---
V1 -> V2: subject typos
V2 -> V3: move the check before kmalloc

 drivers/media/usb/dvb-usb/pctv452e.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/media/usb/dvb-usb/pctv452e.c b/drivers/media/usb/dvb-usb/pctv452e.c
index 5094de9a312e..bc7a224d829e 100644
--- a/drivers/media/usb/dvb-usb/pctv452e.c
+++ b/drivers/media/usb/dvb-usb/pctv452e.c
@@ -422,16 +422,15 @@ static int pctv452e_i2c_msg(struct dvb_usb_device *d, u8 addr,
 	u8 id;
 	int ret;
 
+	if (snd_len > 64 - 7 || rcv_len > 64 - 7)
+		return -EINVAL;
+
 	buf = kmalloc(64, GFP_KERNEL);
 	if (!buf)
 		return -ENOMEM;
 
 	id = state->c++;
 
-	ret = -EINVAL;
-	if (snd_len > 64 - 7 || rcv_len > 64 - 7)
-		goto failed;
-
 	buf[0] = SYNC_BYTE_OUT;
 	buf[1] = id;
 	buf[2] = PCTV_CMD_I2C;
-- 
2.43.0