[PATCH 5.13 649/800] char: pcmcia: error out if num_bytes_read is greater than 4 in set_protocol()

[Greg Kroah-Hartman]

From: Yu Kuai <yukuai3@xxxxxxxxxx>

[ Upstream commit 37188559c610f1b7eec83c8e448936c361c578de ]

Theoretically, it will cause index out of bounds error if
'num_bytes_read' is greater than 4. As we expect it(and was tested)
never to be greater than 4, error out if it happens.

Fixes: c1986ee9bea3 ("[PATCH] New Omnikey Cardman 4000 driver")
Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20210521120617.138396-1-yukuai3@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/char/pcmcia/cm4000_cs.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/char/pcmcia/cm4000_cs.c b/drivers/char/pcmcia/cm4000_cs.c
index 89681f07bc78..9468e9520cee 100644
--- a/drivers/char/pcmcia/cm4000_cs.c
+++ b/drivers/char/pcmcia/cm4000_cs.c
@@ -544,6 +544,10 @@ static int set_protocol(struct cm4000_dev *dev, struct ptsreq *ptsreq)
 		io_read_num_rec_bytes(iobase, &num_bytes_read);
 		if (num_bytes_read >= 4) {
 			DEBUGP(2, dev, "NumRecBytes = %i\n", num_bytes_read);
+			if (num_bytes_read > 4) {
+				rc = -EIO;
+				goto exit_setprotocol;
+			}
 			break;
 		}
 		usleep_range(10000, 11000);
-- 
2.30.2