linux-kernel - [PATCH] Input: iforce - invert valid length check when fetching device IDs

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Date:   Mon, 7 Nov 2022 19:47:15 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Greg Tulli <greg.iforce@...il.com>
Cc:     syzbot <syzbot+4dd880c1184280378821@...kaller.appspotmail.com>,
        syzkaller-bugs@...glegroups.com, linux-input@...r.kernel.org,
        linux-kernel@...r.kernel.org, glider@...gle.com
Subject: [PATCH] Input: iforce - invert valid length check when fetching
 device IDs

syzbot is reporting uninitialized value at iforce_init_device() [1], for
commit 6ac0aec6b0a6 ("Input: iforce - allow callers supply data buffer
when fetching device IDs") is checking that valid length is shorter than
bytes to read. Since iforce_get_id_packet() stores valid length when
returning 0, the caller needs to check that valid length is longer than or
equals to bytes to read.

Link: https://syzkaller.appspot.com/bug?extid=4dd880c1184280378821 [1]
Reported-by: syzbot <syzbot+4dd880c1184280378821@...kaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Fixes: 6ac0aec6b0a6 ("Input: iforce - allow callers supply data buffer when fetching device IDs")
---
 drivers/input/joystick/iforce/iforce-main.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/input/joystick/iforce/iforce-main.c b/drivers/input/joystick/iforce/iforce-main.c
index b86de1312512..84b87526b7ba 100644
--- a/drivers/input/joystick/iforce/iforce-main.c
+++ b/drivers/input/joystick/iforce/iforce-main.c
@@ -273,22 +273,22 @@ int iforce_init_device(struct device *parent, u16 bustype,
  * Get device info.
  */
 
-	if (!iforce_get_id_packet(iforce, 'M', buf, &len) || len < 3)
+	if (!iforce_get_id_packet(iforce, 'M', buf, &len) && len >= 3)
 		input_dev->id.vendor = get_unaligned_le16(buf + 1);
 	else
 		dev_warn(&iforce->dev->dev, "Device does not respond to id packet M\n");
 
-	if (!iforce_get_id_packet(iforce, 'P', buf, &len) || len < 3)
+	if (!iforce_get_id_packet(iforce, 'P', buf, &len) && len >= 3)
 		input_dev->id.product = get_unaligned_le16(buf + 1);
 	else
 		dev_warn(&iforce->dev->dev, "Device does not respond to id packet P\n");
 
-	if (!iforce_get_id_packet(iforce, 'B', buf, &len) || len < 3)
+	if (!iforce_get_id_packet(iforce, 'B', buf, &len) && len >= 3)
 		iforce->device_memory.end = get_unaligned_le16(buf + 1);
 	else
 		dev_warn(&iforce->dev->dev, "Device does not respond to id packet B\n");
 
-	if (!iforce_get_id_packet(iforce, 'N', buf, &len) || len < 2)
+	if (!iforce_get_id_packet(iforce, 'N', buf, &len) && len >= 2)
 		ff_effects = buf[1];
 	else
 		dev_warn(&iforce->dev->dev, "Device does not respond to id packet N\n");
-- 
2.18.4