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Date:   Wed, 27 Nov 2019 10:07:11 -0500 (EST)
From:   Alan Stern <stern@rowland.harvard.edu>
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To:     Pete Zaitcev <zaitcev@redhat.com>
cc:     Greg KH <greg@kroah.com>, USB list <linux-usb@vger.kernel.org>
Subject: Re: [PATCH] usb: mon: Fix a deadlock in usbmon between mmap and read
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On Tue, 26 Nov 2019, Pete Zaitcev wrote:

> On Tue, 26 Nov 2019 10:20:14 -0500 (EST)
> Alan Stern <stern@rowland.harvard.edu> wrote:
> 
> > > Signed-off-by: Pete Zaitcev <zaitcev@redhat.com>
> > > Reported-by: syzbot+56f9673bb4cdcbeb0e92@syzkaller.appspotmail.com  
> > 
> > Reviewed-by: Alan Stern <stern@rowland.harvard.edu>
> 
> Thanks.
> 
> > Fixes: 46eb14a6e158 ("USB: fix usbmon BUG trigger")
> 
> Indeed... Either I didn't think that one through, or the copy_to_user
> used not to take the mmap_sem.

copy_to_user doesn't, but the fault handler does (the core handler, not
the fault routine in mon_bin.c).  After all, it doesn't want the memory
map to change while a page is being read in to satisfy the fault.

Alan Stern