linux-kernel - [PATCH] usb: gadget: prevent a ternary sign expansion bug

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Date:   Thu, 22 Apr 2021 12:00:54 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Felipe Balbi <balbi@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Jens Axboe <axboe@...nel.dk>,
        Felix Kuehling <Felix.Kuehling@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Zhang Qilong <zhangqilong3@...wei.com>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Subject: [PATCH] usb: gadget: prevent a ternary sign expansion bug

The problem is that "req->actual" is a u32, "req->status" is an int, and
iocb->ki_complete() takes a long.  We would expect that a negative error
code in "req->status" would translate to a negative long value.

But what actually happens is that because "req->actual" is a u32, the
error codes is type promoted to a high positive value and then remains
a positive value when it is cast to long.  (No sign expansion).

We can fix this by casting "req->status" to long.

Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
---
 drivers/usb/gadget/legacy/inode.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/gadget/legacy/inode.c b/drivers/usb/gadget/legacy/inode.c
index 71e7d10dd76b..cd8e2737947b 100644
--- a/drivers/usb/gadget/legacy/inode.c
+++ b/drivers/usb/gadget/legacy/inode.c
@@ -498,7 +498,8 @@ static void ep_aio_complete(struct usb_ep *ep, struct usb_request *req)
 		iocb->private = NULL;
 		/* aio_complete() reports bytes-transferred _and_ faults */
 
-		iocb->ki_complete(iocb, req->actual ? req->actual : req->status,
+		iocb->ki_complete(iocb,
+				req->actual ? req->actual : (long)req->status,
 				req->status);
 	} else {
 		/* ep_copy_to_user() won't report both; we hide some faults */
-- 
2.30.2