linux-kernel - Re: [PATCH] usb: host: ehci-sched: avoid possible NULL dereference

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Message-ID: <20201006175845.GC423499@rowland.harvard.edu>
Date:   Tue, 6 Oct 2020 13:58:45 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Sudip Mukherjee <sudipm.mukherjee@...il.com>
Cc:     "Harley A.W. Lorenzo" <hl1998@...tonmail.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-safety@...ts.elisa.tech" <linux-safety@...ts.elisa.tech>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
Subject: Re: [PATCH] usb: host: ehci-sched: avoid possible NULL dereference

On Mon, Oct 05, 2020 at 09:25:44PM -0400, stern@...land.harvard.edu wrote:
> On Mon, Oct 05, 2020 at 11:19:02PM +0000, Harley A.W. Lorenzo wrote:
> > On Monday, October 5, 2020 5:31 PM, Sudip Mukherjee <sudipm.mukherjee@...il.com> wrote:
> > 
> > > find_tt() can return NULL or the error value in ERR_PTR() and
> > > dereferencing the return value without checking for the error can
> > > lead to a possible dereference of NULL pointer or ERR_PTR().
> > 
> > Looks fine to me. There is in fact no checks of the return value
> > before a dereference here, and this solves that.
> > 
> > Reviewed-by: Harley A.W. Lorenzo <hl1998@...tonmail.com
> 
> No, this patch is wrong.  In fact, these calls to find_tt() cannot 
> return NULL or an ERR_PTR value.

Sudip, if you would prefer to submit a patch that adds comments to those 
call sites explaining that find_tt() will not return NULL or an error, 
that would be okay.

Alan Stern