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Date:   Wed, 2 Sep 2020 14:58:27 +0200
From:   Pavel Machek <pavel@denx.de>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        Alan Stern <stern@rowland.harvard.edu>,
        syzbot+c2c3302f9c601a4b1be2@syzkaller.appspotmail.com
Subject: Re: [PATCH 4.19 108/125] USB: yurex: Fix bad gfp argument
Message-ID: <20200902125827.GA8817@duo.ucw.cz>
References: <20200901150934.576210879@linuxfoundation.org>
 <20200901150939.905188730@linuxfoundation.org>
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Hi!

> The syzbot fuzzer identified a bug in the yurex driver: It passes
> GFP_KERNEL as a memory-allocation flag to usb_submit_urb() at a time
> when its state is TASK_INTERRUPTIBLE, not TASK_RUNNING:

Yeah, and instead of fixing the bug, patch papers over it, reducing
reliability of the driver in the process.

> This patch changes the call to use GFP_ATOMIC instead of GFP_KERNEL.

Fixing it properly should be as simple as moving prepare_to_wait down,
no?

Signed-off-by: Pavel Machek (CIP) <pavel@denx.de>

diff --git a/drivers/usb/misc/yurex.c b/drivers/usb/misc/yurex.c
index 785080f79073..5fbbb57e6e95 100644
--- a/drivers/usb/misc/yurex.c
+++ b/drivers/usb/misc/yurex.c
@@ -489,10 +489,10 @@ static ssize_t yurex_write(struct file *file, const c=
har __user *user_buffer,
 	}
=20
 	/* send the data as the control msg */
-	prepare_to_wait(&dev->waitq, &wait, TASK_INTERRUPTIBLE);
 	dev_dbg(&dev->interface->dev, "%s - submit %c\n", __func__,
 		dev->cntl_buffer[0]);
-	retval =3D usb_submit_urb(dev->cntl_urb, GFP_ATOMIC);
+	retval =3D usb_submit_urb(dev->cntl_urb, GFP_KERNEL);
+	prepare_to_wait(&dev->waitq, &wait, TASK_INTERRUPTIBLE);
 	if (retval >=3D 0)
 		timeout =3D schedule_timeout(YUREX_WRITE_TIMEOUT);
 	finish_wait(&dev->waitq, &wait);


Best regards,
									Pavel

--=20
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blo=
g.html

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