Re: [PATCH] platform/chrome: cros_ec_dev - Fix security issue

[Lee Jones <lee.jones@linaro.org>]

On Thu, 18 Mar 2021, Greg KH wrote:

> On Thu, Mar 18, 2021 at 07:54:43AM +0000, Lee Jones wrote:
> > On Wed, 17 Mar 2021, Gwendal Grignou wrote:
> > 
> > > commit 5d749d0bbe811c10d9048cde6dfebc761713abfd upstream.
> > > 
> > > Prevent memory scribble by checking that ioctl buffer size parameters
> > > are sane.
> > > Without this check, on 32 bits system, if .insize = 0xffffffff - 20 and
> > > .outsize the amount to scribble, we would overflow, allocate a small
> > > amounts and be able to write outside of the malloc'ed area.
> > > Adding a hard limit allows argument checking of the ioctl. With the
> > > current EC, it is expected .insize and .outsize to be at around 512 bytes
> > > or less.
> > > 
> > > Signed-off-by: Olof Johansson <olof@lixom.net>
> > > Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
> > > ---
> > >  drivers/platform/chrome/cros_ec_dev.c   | 4 ++++
> > >  drivers/platform/chrome/cros_ec_proto.c | 4 ++--
> > >  include/linux/mfd/cros_ec.h             | 6 ++++--
> > >  3 files changed, 10 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/drivers/platform/chrome/cros_ec_dev.c b/drivers/platform/chrome/cros_ec_dev.c
> > > index 2b331d5b9e799..e16d82bb36a9d 100644
> > > --- a/drivers/platform/chrome/cros_ec_dev.c
> > > +++ b/drivers/platform/chrome/cros_ec_dev.c
> > > @@ -137,6 +137,10 @@ static long ec_device_ioctl_xcmd(struct cros_ec_dev *ec, void __user *arg)
> > >  	if (copy_from_user(&u_cmd, arg, sizeof(u_cmd)))
> > >  		return -EFAULT;
> > >  
> > > +	if ((u_cmd.outsize > EC_MAX_MSG_BYTES) ||
> > > +	    (u_cmd.insize > EC_MAX_MSG_BYTES))
> > > +		return -EINVAL;
> > > +
> > >  	s_cmd = kmalloc(sizeof(*s_cmd) + max(u_cmd.outsize, u_cmd.insize),
> > >  			GFP_KERNEL);
> > >  	if (!s_cmd)
> > > diff --git a/drivers/platform/chrome/cros_ec_proto.c b/drivers/platform/chrome/cros_ec_proto.c
> > > index 5c285f2b3a650..d20190c8f0c06 100644
> > > --- a/drivers/platform/chrome/cros_ec_proto.c
> > > +++ b/drivers/platform/chrome/cros_ec_proto.c
> > > @@ -311,8 +311,8 @@ int cros_ec_query_all(struct cros_ec_device *ec_dev)
> > >  			ec_dev->max_response = EC_PROTO2_MAX_PARAM_SIZE;
> > >  			ec_dev->max_passthru = 0;
> > >  			ec_dev->pkt_xfer = NULL;
> > > -			ec_dev->din_size = EC_MSG_BYTES;
> > > -			ec_dev->dout_size = EC_MSG_BYTES;
> > > +			ec_dev->din_size = EC_PROTO2_MSG_BYTES;
> > > +			ec_dev->dout_size = EC_PROTO2_MSG_BYTES;
> > >  		} else {
> > >  			/*
> > >  			 * It's possible for a test to occur too early when
> > > diff --git a/include/linux/mfd/cros_ec.h b/include/linux/mfd/cros_ec.h
> > > index 3ab3cede28eac..93c14e9df6309 100644
> > > --- a/include/linux/mfd/cros_ec.h
> > > +++ b/include/linux/mfd/cros_ec.h
> > > @@ -50,9 +50,11 @@ enum {
> > >  					EC_MSG_TX_TRAILER_BYTES,
> > >  	EC_MSG_RX_PROTO_BYTES	= 3,
> > >  
> > > -	/* Max length of messages */
> > > -	EC_MSG_BYTES		= EC_PROTO2_MAX_PARAM_SIZE +
> > > +	/* Max length of messages for proto 2*/
> > > +	EC_PROTO2_MSG_BYTES		= EC_PROTO2_MAX_PARAM_SIZE +
> > >  					EC_MSG_TX_PROTO_BYTES,
> > 
> > Nit: Better to not tab the '=' so far and place it all on one line.
> > 
> > Checkpatch now only complains about lines exceeding 100 chars.
> > 
> > Once fixed, feel free to apply my:
> > 
> >   Acked-by: Lee Jones <lee.jones@linaro.org>
> 
> This commit is already in 4.7, and is from 2016, so I don't know why you
> are reviewing it :)

Heh!  It looked like a standard patch at first glance.

Must have skipped over the "commit" line in the commit log.

I wonder why it doesn't have my Ack on it already then?

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
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