linux-kernel - Re: [PATCH] clk: imx: Fix a NULL pointer dereference in imx_register_uart

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Date:   Fri, 28 Jan 2022 07:47:06 -0600
From:   Adam Ford <aford173@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Zhou Qingyang <zhou1615@....edu>, kjlu@....edu,
        Abel Vesa <abel.vesa@....com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        linux-clk <linux-clk@...r.kernel.org>,
        arm-soc <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] clk: imx: Fix a NULL pointer dereference in imx_register_uart_clocks()

On Fri, Jan 28, 2022 at 4:16 AM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> On Tue, Jan 25, 2022 at 12:52:06AM +0800, Zhou Qingyang wrote:
> > In imx_register_uart_clocks(), the global variable imx_uart_clocks is
> > assigned by kcalloc() and there is a dereference of in the next for loop,
> > which could introduce a NULL pointer dereference on failure of kcalloc().
> >
> > Fix this by adding a NULL check of imx_uart_clocks.
> >
> > This bug was found by a static analyzer.
> >
> > Builds with 'make allyesconfig' show no new warnings,
> > and our static analyzer no longer warns about this code.
> >
> > Fixes: 379c9a24cc23 ("clk: imx: Fix reparenting of UARTs not associated with stdout")
> > Signed-off-by: Zhou Qingyang <zhou1615@....edu>
> > ---
> > The analysis employs differential checking to identify inconsistent
> > security operations (e.g., checks or kfrees) between two code paths
> > and confirms that the inconsistent operations are not recovered in the
> > current function or the callers, so they constitute bugs.
> >
> > Note that, as a bug found by static analysis, it can be a false
> > positive or hard to trigger. Multiple researchers have cross-reviewed
> > the bug.
> >
> >  drivers/clk/imx/clk.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/clk/imx/clk.c b/drivers/clk/imx/clk.c
> > index 7cc669934253..99249ab361d2 100644
> > --- a/drivers/clk/imx/clk.c
> > +++ b/drivers/clk/imx/clk.c
> > @@ -173,6 +173,8 @@ void imx_register_uart_clocks(unsigned int clk_count)
> >               int i;
> >
> >               imx_uart_clocks = kcalloc(clk_count, sizeof(struct clk *), GFP_KERNEL);
> > +             if (!imx_uart_clocks)
> > +                     return;
> >
> >               if (!of_stdout)
> >                       return;
> > --
> > 2.25.1
> >
>
> As stated before, umn.edu is still not allowed to contribute to the
> Linux kernel.  Please work with your administration to resolve this
> issue.

Greg,

In the interest of safety, I believe this patch is reasonable.  I
wrote the original patch that is being fixed by this.  Would it be
acceptable if I submitted the same patch with "suggested-by"
associated with Zhou @ umn.edu?  I want to give credit where credit is
due while still maintaining the rule that patches are not actually
being accepted by umn.edu.

adam