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

[Edward Adam Davis]

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+480edd...@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=480edd2cadb85ddb4bbe
Signed-off-by: Edward Adam Davis <ead...@qq.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