[media] pctv452e: move buffer to heap, no mutex

commit 73d5c5c8 ("[media] pctv452e: don't do DMA on stack") caused
a NULL pointer dereference which occurs when dvb_usb_init()
calls dvb_usb_device_power_ctrl() for the first time, before the
frontend has been attached. It also caused a recursive deadlock because
tt3650_ci_msg_locked() has already locked the mutex.

So, partially revert it, but move the buffer to the heap
(DMA capable), not to the stack (may not be DMA capable).
Instead of sharing one buffer which needs mutex protection,
do a new heap allocation for each call.

Fixes: commit 73d5c5c8 ("[media] pctv452e: don't do DMA on stack")

Cc: stable@vger.kernel.org # For Kernel 4.9
Signed-off-by: Max Kellermann <max.kellermann@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/usb/dvb-usb/pctv452e.c

@@ -97,14 +97,13 @@ struct pctv452e_state {
 	u8 c;	   /* transaction counter, wraps around...  */
 	u8 initialized; /* set to 1 if 0x15 has been sent */
 	u16 last_rc_key;
-
-	unsigned char data[80];
 };
 
 static int tt3650_ci_msg(struct dvb_usb_device *d, u8 cmd, u8 *data,
 			 unsigned int write_len, unsigned int read_len)
 {
 	struct pctv452e_state *state = (struct pctv452e_state *)d->priv;
+	u8 *buf;
 	u8 id;
 	unsigned int rlen;
 	int ret;
@@ -114,36 +113,39 @@ static int tt3650_ci_msg(struct dvb_usb_device *d, u8 cmd, u8 *data,
 		return -EIO;
 	}
 
-	mutex_lock(&state->ca_mutex);
+	buf = kmalloc(64, GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+
 	id = state->c++;
 
-	state->data[0] = SYNC_BYTE_OUT;
-	state->data[1] = id;
-	state->data[2] = cmd;
-	state->data[3] = write_len;
+	buf[0] = SYNC_BYTE_OUT;
+	buf[1] = id;
+	buf[2] = cmd;
+	buf[3] = write_len;
 
-	memcpy(state->data + 4, data, write_len);
+	memcpy(buf + 4, data, write_len);
 
 	rlen = (read_len > 0) ? 64 : 0;
-	ret = dvb_usb_generic_rw(d, state->data, 4 + write_len,
-				  state->data, rlen, /* delay_ms */ 0);
+	ret = dvb_usb_generic_rw(d, buf, 4 + write_len,
+				  buf, rlen, /* delay_ms */ 0);
 	if (0 != ret)
 		goto failed;
 
 	ret = -EIO;
-	if (SYNC_BYTE_IN != state->data[0] || id != state->data[1])
+	if (SYNC_BYTE_IN != buf[0] || id != buf[1])
 		goto failed;
 
-	memcpy(data, state->data + 4, read_len);
+	memcpy(data, buf + 4, read_len);
 
-	mutex_unlock(&state->ca_mutex);
+	kfree(buf);
 	return 0;
 
 failed:
 	err("CI error %d; %02X %02X %02X -> %*ph.",
-	     ret, SYNC_BYTE_OUT, id, cmd, 3, state->data);
+	     ret, SYNC_BYTE_OUT, id, cmd, 3, buf);
 
-	mutex_unlock(&state->ca_mutex);
+	kfree(buf);
 	return ret;
 }
 
@@ -410,53 +412,57 @@ static int pctv452e_i2c_msg(struct dvb_usb_device *d, u8 addr,
 				u8 *rcv_buf, u8 rcv_len)
 {
 	struct pctv452e_state *state = (struct pctv452e_state *)d->priv;
+	u8 *buf;
 	u8 id;
 	int ret;
 
-	mutex_lock(&state->ca_mutex);
+	buf = kmalloc(64, GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+
 	id = state->c++;
 
 	ret = -EINVAL;
 	if (snd_len > 64 - 7 || rcv_len > 64 - 7)
 		goto failed;
 
-	state->data[0] = SYNC_BYTE_OUT;
-	state->data[1] = id;
-	state->data[2] = PCTV_CMD_I2C;
-	state->data[3] = snd_len + 3;
-	state->data[4] = addr << 1;
-	state->data[5] = snd_len;
-	state->data[6] = rcv_len;
+	buf[0] = SYNC_BYTE_OUT;
+	buf[1] = id;
+	buf[2] = PCTV_CMD_I2C;
+	buf[3] = snd_len + 3;
+	buf[4] = addr << 1;
+	buf[5] = snd_len;
+	buf[6] = rcv_len;
 
-	memcpy(state->data + 7, snd_buf, snd_len);
+	memcpy(buf + 7, snd_buf, snd_len);
 
-	ret = dvb_usb_generic_rw(d, state->data, 7 + snd_len,
-				  state->data, /* rcv_len */ 64,
+	ret = dvb_usb_generic_rw(d, buf, 7 + snd_len,
+				  buf, /* rcv_len */ 64,
 				  /* delay_ms */ 0);
 	if (ret < 0)
 		goto failed;
 
 	/* TT USB protocol error. */
 	ret = -EIO;
-	if (SYNC_BYTE_IN != state->data[0] || id != state->data[1])
+	if (SYNC_BYTE_IN != buf[0] || id != buf[1])
 		goto failed;
 
 	/* I2C device didn't respond as expected. */
 	ret = -EREMOTEIO;
-	if (state->data[5] < snd_len || state->data[6] < rcv_len)
+	if (buf[5] < snd_len || buf[6] < rcv_len)
 		goto failed;
 
-	memcpy(rcv_buf, state->data + 7, rcv_len);
-	mutex_unlock(&state->ca_mutex);
+	memcpy(rcv_buf, buf + 7, rcv_len);
 
+	kfree(buf);
 	return rcv_len;
 
 failed:
 	err("I2C error %d; %02X %02X  %02X %02X %02X -> %*ph",
 	     ret, SYNC_BYTE_OUT, id, addr << 1, snd_len, rcv_len,
-	     7, state->data);
+	     7, buf);
 
-	mutex_unlock(&state->ca_mutex);
+	kfree(buf);
 	return ret;
 }
 
@@ -505,7 +511,7 @@ static u32 pctv452e_i2c_func(struct i2c_adapter *adapter)
 static int pctv452e_power_ctrl(struct dvb_usb_device *d, int i)
 {
 	struct pctv452e_state *state = (struct pctv452e_state *)d->priv;
-	u8 *rx;
+	u8 *b0, *rx;
 	int ret;
 
 	info("%s: %d\n", __func__, i);
@@ -516,11 +522,12 @@ static int pctv452e_power_ctrl(struct dvb_usb_device *d, int i)
 	if (state->initialized)
 		return 0;
 
-	rx = kmalloc(PCTV_ANSWER_LEN, GFP_KERNEL);
-	if (!rx)
+	b0 = kmalloc(5 + PCTV_ANSWER_LEN, GFP_KERNEL);
+	if (!b0)
 		return -ENOMEM;
 
-	mutex_lock(&state->ca_mutex);
+	rx = b0 + 5;
+
 	/* hmm where shoud this should go? */
 	ret = usb_set_interface(d->udev, 0, ISOC_INTERFACE_ALTERNATIVE);
 	if (ret != 0)
@@ -528,66 +535,70 @@ static int pctv452e_power_ctrl(struct dvb_usb_device *d, int i)
 			__func__, ret);
 
 	/* this is a one-time initialization, dont know where to put */
-	state->data[0] = 0xaa;
-	state->data[1] = state->c++;
-	state->data[2] = PCTV_CMD_RESET;
-	state->data[3] = 1;
-	state->data[4] = 0;
+	b0[0] = 0xaa;
+	b0[1] = state->c++;
+	b0[2] = PCTV_CMD_RESET;
+	b0[3] = 1;
+	b0[4] = 0;
 	/* reset board */
-	ret = dvb_usb_generic_rw(d, state->data, 5, rx, PCTV_ANSWER_LEN, 0);
+	ret = dvb_usb_generic_rw(d, b0, 5, rx, PCTV_ANSWER_LEN, 0);
 	if (ret)
 		goto ret;
 
-	state->data[1] = state->c++;
-	state->data[4] = 1;
+	b0[1] = state->c++;
+	b0[4] = 1;
 	/* reset board (again?) */
-	ret = dvb_usb_generic_rw(d, state->data, 5, rx, PCTV_ANSWER_LEN, 0);
+	ret = dvb_usb_generic_rw(d, b0, 5, rx, PCTV_ANSWER_LEN, 0);
 	if (ret)
 		goto ret;
 
 	state->initialized = 1;
 
 ret:
-	mutex_unlock(&state->ca_mutex);
-	kfree(rx);
+	kfree(b0);
 	return ret;
 }
 
 static int pctv452e_rc_query(struct dvb_usb_device *d)
 {
 	struct pctv452e_state *state = (struct pctv452e_state *)d->priv;
+	u8 *b, *rx;
 	int ret, i;
 	u8 id;
 
-	mutex_lock(&state->ca_mutex);
+	b = kmalloc(CMD_BUFFER_SIZE + PCTV_ANSWER_LEN, GFP_KERNEL);
+	if (!b)
+		return -ENOMEM;
+
+	rx = b + CMD_BUFFER_SIZE;
+
 	id = state->c++;
 
 	/* prepare command header  */
-	state->data[0] = SYNC_BYTE_OUT;
-	state->data[1] = id;
-	state->data[2] = PCTV_CMD_IR;
-	state->data[3] = 0;
+	b[0] = SYNC_BYTE_OUT;
+	b[1] = id;
+	b[2] = PCTV_CMD_IR;
+	b[3] = 0;
 
 	/* send ir request */
-	ret = dvb_usb_generic_rw(d, state->data, 4,
-				 state->data, PCTV_ANSWER_LEN, 0);
+	ret = dvb_usb_generic_rw(d, b, 4, rx, PCTV_ANSWER_LEN, 0);
 	if (ret != 0)
 		goto ret;
 
 	if (debug > 3) {
-		info("%s: read: %2d: %*ph: ", __func__, ret, 3, state->data);
-		for (i = 0; (i < state->data[3]) && ((i + 3) < PCTV_ANSWER_LEN); i++)
-			info(" %02x", state->data[i + 3]);
+		info("%s: read: %2d: %*ph: ", __func__, ret, 3, rx);
+		for (i = 0; (i < rx[3]) && ((i+3) < PCTV_ANSWER_LEN); i++)
+			info(" %02x", rx[i+3]);
 
 		info("\n");
 	}
 
-	if ((state->data[3] == 9) &&  (state->data[12] & 0x01)) {
+	if ((rx[3] == 9) &&  (rx[12] & 0x01)) {
 		/* got a "press" event */
-		state->last_rc_key = RC_SCANCODE_RC5(state->data[7], state->data[6]);
+		state->last_rc_key = RC_SCANCODE_RC5(rx[7], rx[6]);
 		if (debug > 2)
 			info("%s: cmd=0x%02x sys=0x%02x\n",
-				__func__, state->data[6], state->data[7]);
+				__func__, rx[6], rx[7]);
 
 		rc_keydown(d->rc_dev, RC_TYPE_RC5, state->last_rc_key, 0);
 	} else if (state->last_rc_key) {
@@ -595,7 +606,7 @@ static int pctv452e_rc_query(struct dvb_usb_device *d)
 		state->last_rc_key = 0;
 	}
 ret:
-	mutex_unlock(&state->ca_mutex);
+	kfree(b);
 	return ret;
 }