platform/chrome: cros_ec_dev - Fix security issue

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(-)

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 :)

thanks,

greg k-h