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

From: "Sudip Mukherjee" <sudip.mukherjee@codethink.co.uk>
To: "development-process@lists.elisa.tech"
	<development-process@lists.elisa.tech>,
	linux-safety@lists.elisa.tech
Subject: Re: [linux-safety] [PATCH] usb: host: ehci-sched: avoid possible NULL dereference
Date: Tue, 6 Oct 2020 09:31:33 +0100	[thread overview]
Message-ID: <3052d0a3-f482-ca91-3ad6-950c5296a92c@codethink.co.uk> (raw)
In-Reply-To: <20201005213149.12332-1-sudipm.mukherjee@gmail.com>

Hi All,

I sent out this patch yesterday which I think is an obvious safety issue
as the error was not handled. This is a change in code and the resultant
binary will not be same. I know we are moving to pcie now, but have we
decided yet how to validate these kinds of changes?

-- 
Regards
Sudip

On 05/10/2020 22:31, Sudip Mukherjee 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().
> 
> Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
> ---
>  drivers/usb/host/ehci-sched.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/usb/host/ehci-sched.c b/drivers/usb/host/ehci-sched.c
> index 6dfb242f9a4b..f3fd7e9fe6b2 100644
> --- a/drivers/usb/host/ehci-sched.c
> +++ b/drivers/usb/host/ehci-sched.c
> @@ -245,6 +245,8 @@ static void reserve_release_intr_bandwidth(struct ehci_hcd *ehci,
>  	/* FS/LS bus bandwidth */
>  	if (tt_usecs) {
>  		tt = find_tt(qh->ps.udev);
> +		if (IS_ERR_OR_NULL(tt))
> +			return;
>  		if (sign > 0)
>  			list_add_tail(&qh->ps.ps_list, &tt->ps_list);
>  		else
> @@ -1338,6 +1340,8 @@ static void reserve_release_iso_bandwidth(struct ehci_hcd *ehci,
>  		}
>  
>  		tt = find_tt(stream->ps.udev);
> +		if (IS_ERR_OR_NULL(tt))
> +			return;
>  		if (sign > 0)
>  			list_add_tail(&stream->ps.ps_list, &tt->ps_list);
>  		else
> 