Re: [RFC] [media] dvb-core: check ->msg_len for diseqc_send_master_cmd()

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On 04/17/2013 03:03 PM, Dan Carpenter wrote:
Any feedback on this?

I forgot to CC Steven Toth last time because he would know about the
cx24116 driver.  I've looked at it again and it still looks like
cx24116_send_diseqc_msg() is copying garbage into the
state->dsec_cmd.args[] array.

It looks fine. I have thought that same few times earlier too. Thank you.

Reviewed-by: Antti Palosaari <crope@xxxxxx>




regards,
dan carpenter

On Tue, Apr 02, 2013 at 10:51:02AM +0300, Dan Carpenter wrote:
I'd like to send this patch except that it "breaks"
cx24116_send_diseqc_msg().  The cx24116 driver accepts ->msg_len values
up to 24 but it looks like it's just copying 16 bytes past the end of
the ->msg[] array so it's already broken.

cmd->msg_len is an unsigned char.  The comment next to the struct
declaration says that valid values are are 3-6.  Some of the drivers
check that this is true, but most don't and it could cause memory
corruption.

Some examples of functions which don't check are:
ttusbdecfe_dvbs_diseqc_send_master_cmd()
cx24123_send_diseqc_msg()
ds3000_send_diseqc_msg()
etc.

Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>

diff --git a/drivers/media/dvb-core/dvb_frontend.c b/drivers/media/dvb-core/dvb_frontend.c
index 57601c0..3d1eee6 100644
--- a/drivers/media/dvb-core/dvb_frontend.c
+++ b/drivers/media/dvb-core/dvb_frontend.c
@@ -2265,7 +2265,13 @@ static int dvb_frontend_ioctl_legacy(struct file *file,

  	case FE_DISEQC_SEND_MASTER_CMD:
  		if (fe->ops.diseqc_send_master_cmd) {
-			err = fe->ops.diseqc_send_master_cmd(fe, (struct dvb_diseqc_master_cmd*) parg);
+			struct dvb_diseqc_master_cmd *cmd = parg;
+
+			if (cmd->msg_len >= 3 && cmd->msg_len <= 6)
+				err = fe->ops.diseqc_send_master_cmd(fe, cmd);
+			else
+				err = -EINVAL;
+
  			fepriv->state = FESTATE_DISEQC;
  			fepriv->status = 0;
  		}


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