linux-kernel - RE: [PATCH] net: arc_emac: Fix use after free in arc_mdio

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Date:   Tue, 8 Mar 2022 13:50:40 +0000
From:   "Cai,Huoqing" <caihuoqing@...du.com>
To:     Andrew Lunn <andrew@...n.ch>,
        Jianglei Nie <niejianglei2021@....com>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] net: arc_emac: Fix use after free in arc_mdio_probe()

Hello,

> -----Original Message-----
> From: Andrew Lunn <andrew@...n.ch>
> Sent: 2022年3月8日 21:43
> To: Jianglei Nie
> Cc: davem@...emloft.net; kuba@...nel.org; Cai,Huoqing;
> netdev@...r.kernel.org; linux-kernel@...r.kernel.org
> Subject: Re: [PATCH] net: arc_emac: Fix use after free in arc_mdio_probe()
If resend a patch,  you can use prefix "[PATCH v2]" in subject.
e.g.  git format-patch -1 -v2
> 
> On Tue, Mar 08, 2022 at 07:10:05PM +0800, Jianglei Nie wrote:
> > If bus->state is equal to MDIOBUS_ALLOCATED, mdiobus_free(bus) will
> free
> > the "bus". But bus->name is still used in the next line, which will lead
> > to a use after free.
> >
> > We can fix it by putting the bus->name in a local variable and then use
> > the name in the error message without referring to bus to avoid the uaf.
> >
> > Signed-off-by: Jianglei Nie <niejianglei2021@....com>
> > ---
> >  drivers/net/ethernet/arc/emac_mdio.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/arc/emac_mdio.c
> b/drivers/net/ethernet/arc/emac_mdio.c
> > index 9acf589b1178..33fd63d227ef 100644
> > --- a/drivers/net/ethernet/arc/emac_mdio.c
> > +++ b/drivers/net/ethernet/arc/emac_mdio.c
> > @@ -134,6 +134,7 @@ int arc_mdio_probe(struct arc_emac_priv *priv)
> >  	struct device_node *np = priv->dev->of_node;
> >  	struct mii_bus *bus;
> >  	int error;
> > +	const char *name = "Synopsys MII Bus";
> 
> Netdev uses reverse christmass tree, meaning you need to sort
> variables longest to shortest.
> 
> I'm also wondering about the lifetime of name. name itself is a stack
> variable, so it will disappear as soon as the function exits. The
> string itself is in the rodata section. But is a copy made onto the
> stack, or does bus->name point to the rodata?
> 
>        Andrew
> 
> >  	bus = mdiobus_alloc();
> >  	if (!bus)
> > @@ -142,7 +143,7 @@ int arc_mdio_probe(struct arc_emac_priv *priv)
> >  	priv->bus = bus;
> >  	bus->priv = priv;
> >  	bus->parent = priv->dev;
> > -	bus->name = "Synopsys MII Bus";
> > +	bus->name = name;
> >  	bus->read = &arc_mdio_read;
> >  	bus->write = &arc_mdio_write;
> >  	bus->reset = &arc_mdio_reset;
> > @@ -167,7 +168,7 @@ int arc_mdio_probe(struct arc_emac_priv *priv)
> >  	if (error) {
> >  		mdiobus_free(bus);
> >  		return dev_err_probe(priv->dev, error,
> > -				     "cannot register MDIO bus %s\n", bus-
> >name);
> > +				     "cannot register MDIO bus %s\n", name);
> >  	}
> >
> >  	return 0;
> > --
> > 2.25.1
> >