linux-kernel - Re: [syzbot] [kernel?] INFO: task hung in uevent

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Message-ID: <b12dd926-2f81-4feb-a3b0-b7fca2592909@rowland.harvard.edu>
Date: Thu, 10 Jul 2025 10:13:18 -0400
From: Alan Stern <stern@...land.harvard.edu>
To: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc: syzbot <syzbot+592e2ab8775dbe0bf09a@...kaller.appspotmail.com>,
	linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com,
	USB list <linux-usb@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [syzbot] [kernel?] INFO: task hung in uevent_show (2)

On Thu, Jul 10, 2025 at 07:17:19PM +0900, Tetsuo Handa wrote:
> On 2025/07/10 0:41, Alan Stern wrote:
> > Okay, I see what your problem is.
> > 
> > The bEndpointAddress field of the endpoint descriptor is not just the 
> > endpoint's number.  It also includes the endpoint's direction in bit 7 
> > (0 for OUT, 1 for IN).
> 
> I see, but I couldn't figure out whether BUG_ON(endpoint > 0xF) is bad.
> 
> I came up to try these BUG_ON() lines in case some of hung task reports (e.g.
> https://lkml.kernel.org/r/686e8032.050a0220.385921.0006.GAE@google.com ) are
> caused by use of unintended pipes created by out-of-range values being passed
> to __create_pipe().

I think this is unlikely to be the cause of those BUG_ON()s, but go 
ahead and see what happens.

> Should I give up BUG_ON(endpoint > 0xF) line?
> Or should I try to update callers which trigger BUG_ON(endpoint > 0xF) line?

You can change the test to BUG_ON(endpoint & ~0x8F).  That will mask 
away the endpoint number and direction bit, leaving everything else 
alone.

Alan Stern