Commit message: [media] cx24116: fix a buffer overflow when checking userspace params

The maximum size for a DiSEqC command is 6, according to the
userspace API. However, the code allows to write up much more values:
	drivers/media/dvb-frontends/cx24116.c:983 cx24116_send_diseqc_msg() error: buffer overflow 'd->msg' 6 <= 23

Cc: stable@vger.kernel.org
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
CVE: CVE-2015-9289
CWE: CWE-119
Vulnerability description: In the Linux kernel before 4.1.4, a buffer overflow occurs when checking userspace params in drivers/media/dvb-frontends/cx24116.c. The maximum size for a DiSEqC command is 6, according to the userspace API. However, the code allows larger values such as 23.

Project: linux
File: cx24116.c

static int cx24116_send_diseqc_msg(struct dvb_frontend *fe,
	struct dvb_diseqc_master_cmd *d)
{
 	struct cx24116_state *state = fe->demodulator_priv;
 	int i, ret;
 
 	/* Dump DiSEqC message */
 	if (debug) {
 		printk(KERN_INFO "cx24116: %s(", __func__);
		for (i = 0 ; i < d->msg_len ;) {
			printk(KERN_INFO "0x%02x", d->msg[i]);
			if (++i < d->msg_len)
				printk(KERN_INFO ", ");
		}
 		printk(") toneburst=%d\n", toneburst);
 	}
 
	/* Validate length */
	if (d->msg_len > (CX24116_ARGLEN - CX24116_DISEQC_MSGOFS))
		return -EINVAL;
 	/* DiSEqC message */
 	for (i = 0; i < d->msg_len; i++)
 		state->dsec_cmd.args[CX24116_DISEQC_MSGOFS + i] = d->msg[i];

	/* DiSEqC message length */
	state->dsec_cmd.args[CX24116_DISEQC_MSGLEN] = d->msg_len;

	/* Command length */
	state->dsec_cmd.len = CX24116_DISEQC_MSGOFS +
		state->dsec_cmd.args[CX24116_DISEQC_MSGLEN];

	/* DiSEqC toneburst */
	if (toneburst == CX24116_DISEQC_MESGCACHE)
		/* Message is cached */
		return 0;

	else if (toneburst == CX24116_DISEQC_TONEOFF)
		/* Message is sent without burst */
		state->dsec_cmd.args[CX24116_DISEQC_BURST] = 0;

	else if (toneburst == CX24116_DISEQC_TONECACHE) {
		/*
		 * Message is sent with derived else cached burst
		 *
		 * WRITE PORT GROUP COMMAND 38
		 *
		 * 0/A/A: E0 10 38 F0..F3
		 * 1/B/B: E0 10 38 F4..F7
		 * 2/C/A: E0 10 38 F8..FB
		 * 3/D/B: E0 10 38 FC..FF
		 *
		 * databyte[3]= 8421:8421
		 *              ABCD:WXYZ
		 *              CLR :SET
		 *
		 *              WX= PORT SELECT 0..3    (X=TONEBURST)
		 *              Y = VOLTAGE             (0=13V, 1=18V)
		 *              Z = BAND                (0=LOW, 1=HIGH(22K))
		 */
		if (d->msg_len >= 4 && d->msg[2] == 0x38)
			state->dsec_cmd.args[CX24116_DISEQC_BURST] =
				((d->msg[3] & 4) >> 2);
		if (debug)
			dprintk("%s burst=%d\n", __func__,
				state->dsec_cmd.args[CX24116_DISEQC_BURST]);
	}

	/* Wait for LNB ready */
	ret = cx24116_wait_for_lnb(fe);
	if (ret != 0)
		return ret;

	/* Wait for voltage/min repeat delay */
	msleep(100);

	/* Command */
	ret = cx24116_cmd_execute(fe, &state->dsec_cmd);
	if (ret != 0)
		return ret;
	/*
	 * Wait for send
	 *
	 * Eutelsat spec:
	 * >15ms delay          + (XXX determine if FW does this, see set_tone)
	 *  13.5ms per byte     +
	 * >15ms delay          +
	 *  12.5ms burst        +
	 * >15ms delay            (XXX determine if FW does this, see set_tone)
	 */
	msleep((state->dsec_cmd.args[CX24116_DISEQC_MSGLEN] << 4) +
		((toneburst == CX24116_DISEQC_TONEOFF) ? 30 : 60));

	return 0;
}