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

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Message-ID: <20201006012544.GB399825@rowland.harvard.edu>
Date:   Mon, 5 Oct 2020 21:25:44 -0400
From:   "stern@...land.harvard.edu" <stern@...land.harvard.edu>
To:     "Harley A.W. Lorenzo" <hl1998@...tonmail.com>
Cc:     Sudip Mukherjee <sudipm.mukherjee@...il.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 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.

Alan Stern