[PATCH] media firewire firedtv-avc fix a buffer overflow in avc_ca_pmt()

[Yang Yanchao <yangyanchao6@huawei.com>]

For CVE-2021-3542:

1、read_pos will be added four times in the patch, 
so use "read_pos + 4 < length" and write_pos as well

2. The last four bits of c->operand are used for CRC, 
so "sizeof (C - > operand) - 4" is used

3. "read_pos+=2" is added after the end of read_pos, so add value (read_pos >= length)

4. In order to avoid memcpy crossing the boundary, es_ info_ length > length - read_ pos

5. When the date_length is a specific input of a construction,it will cause memcpy
 to exceed the boundary, "(MSG - > MSG [3] & 0x7F) + date_ length) > (sizeof(msg->msg) - 4)"

Signed-off-by: yangyanchao <yangyanchao6@huawei.com>
---
 drivers/media/firewire/firedtv-avc.c | 14 +++++++++++---
 drivers/media/firewire/firedtv-ci.c  |  2 ++
 2 files changed, 13 insertions(+), 3 deletions(-)
diff --git a/drivers/media/firewire/firedtv-avc.c b/drivers/media/firewire/firedtv-avc.c
index 3ef5df164..8c31cf90c 100644
--- a/drivers/media/firewire/firedtv-avc.c
+++ b/drivers/media/firewire/firedtv-avc.c
@@ -1169,7 +1169,11 @@ int avc_ca_pmt(struct firedtv *fdtv, char *msg, int length)
 		read_pos += program_info_length;
 		write_pos += program_info_length;
 	}
-	while (read_pos < length) {
+	while (read_pos + 4 < length) {
+		if (write_pos + 4 >= sizeof(c->operand) - 4) {
+			ret = -EINVAL;
+			goto out;
+		}
 		c->operand[write_pos++] = msg[read_pos++];
 		c->operand[write_pos++] = msg[read_pos++];
 		c->operand[write_pos++] = msg[read_pos++];
@@ -1181,13 +1185,17 @@ int avc_ca_pmt(struct firedtv *fdtv, char *msg, int length)
 		c->operand[write_pos++] = es_info_length >> 8;
 		c->operand[write_pos++] = es_info_length & 0xff;
 		if (es_info_length > 0) {
+			if (read_pos >= length) {
+				ret = -EINVAL;
+				goto out;
+			}
 			pmt_cmd_id = msg[read_pos++];
 			if (pmt_cmd_id != 1 && pmt_cmd_id != 4)
 				dev_err(fdtv->device, "invalid pmt_cmd_id %d at stream level\n",
 					pmt_cmd_id);
 
-			if (es_info_length > sizeof(c->operand) - 4 -
-					     write_pos) {
+			if (es_info_length > sizeof(c->operand) - 4 - write_pos ||
+			    es_info_length > length - read_pos) {
 				ret = -EINVAL;
 				goto out;
 			}
diff --git a/drivers/media/firewire/firedtv-ci.c b/drivers/media/firewire/firedtv-ci.c
index 8dc5a7495..0e7ffa156 100644
--- a/drivers/media/firewire/firedtv-ci.c
+++ b/drivers/media/firewire/firedtv-ci.c
@@ -135,6 +135,8 @@ static int fdtv_ca_pmt(struct firedtv *fdtv, void *arg)
 		data_length = 0;
 		for (i = 0; i < (msg->msg[3] & 0x7f); i++)
 			data_length = (data_length << 8) + msg->msg[data_pos++];
+		if (((msg->msg[3] & 0x7f) + date_length) > (sizeof(msg->msg) - 4))
+			return -EINVAL;
 	} else {
 		data_length = msg->msg[3];
 	}
-- 
2.23.0