[alsa-devel] [PATCH 1/5] ALSA: firewire-lib: add buffer-over-run protection at receiving more data blocks than expected

[Takashi Sakamoto]

In IEC 61883-6, the number of data blocks in a packet is limited up to
the value of SYT_INTERVAL. Current implementation is compliant to the
limitation, while it can cause buffer-over-run when the value of dbs
field in received packet is illegally large.

This commit adds a validator to detect such illegal packets to prevent
the buffer-over-run. Actually, the buffer is aligned to the size of memory
 page, thus this issue hardly causes system errors due to the room to page
alignment, as long as a few packets includes such jumbo payload; i.e.
a packet to several received packets.

Here, Behringer F-Control Audio 202 (based on OXFW 960) has a quirk to
postpone transferring isochronous packet till finish handling any
asynchronous packets. In this case, this model is lazy, transfers no
packets according to several cycle-start packets. After finishing, this
model pushes required data in next isochronous packet. As a result, the
packet include more data blocks than IEC 61883-6 defines.

To continue to support this model, this commit adds a new flag to extend
the length of calculated payload. This flag allows the size of payload
5 times as large as IEC 61883-6 defines. As a result, packets from this
model passed the validator successfully.

Signed-off-by: Takashi Sakamoto <o-takashi at sakamocchi.jp>
---
 sound/firewire/amdtp.c            | 21 +++++++++++++++++++--
 sound/firewire/amdtp.h            |  4 ++++
 sound/firewire/oxfw/oxfw-stream.c | 10 ++++++++--
 3 files changed, 31 insertions(+), 4 deletions(-)

diff --git a/sound/firewire/amdtp.c b/sound/firewire/amdtp.c
index d882ca5..4eb8dc9 100644
--- a/sound/firewire/amdtp.c
+++ b/sound/firewire/amdtp.c
@@ -255,7 +255,12 @@ EXPORT_SYMBOL(amdtp_stream_set_parameters);
  */
 unsigned int amdtp_stream_get_max_payload(struct amdtp_stream *s)
 {
-	return 8 + s->syt_interval * s->data_block_quadlets * 4;
+	unsigned int multiplier = 1;
+
+	if (s->flags & CIP_JUMBO_PAYLOAD)
+		multiplier = 5;
+
+	return 8 + s->syt_interval * s->data_block_quadlets * 4 * multiplier;
 }
 EXPORT_SYMBOL(amdtp_stream_get_max_payload);
 
@@ -811,12 +816,16 @@ static void in_stream_callback(struct fw_iso_context *context, u32 cycle,
 			       void *private_data)
 {
 	struct amdtp_stream *s = private_data;
-	unsigned int p, syt, packets, payload_quadlets;
+	unsigned int p, syt, packets;
+	unsigned int payload_quadlets, max_payload_quadlets;
 	__be32 *buffer, *headers = header;
 
 	/* The number of packets in buffer */
 	packets = header_length / IN_PACKET_HEADER_SIZE;
 
+	/* For buffer-over-run prevention. */
+	max_payload_quadlets = amdtp_stream_get_max_payload(s) / 4;
+
 	for (p = 0; p < packets; p++) {
 		if (s->packet_index < 0)
 			break;
@@ -832,6 +841,14 @@ static void in_stream_callback(struct fw_iso_context *context, u32 cycle,
 		/* The number of quadlets in this packet */
 		payload_quadlets =
 			(be32_to_cpu(headers[p]) >> ISO_DATA_LENGTH_SHIFT) / 4;
+		if (payload_quadlets > max_payload_quadlets) {
+			dev_err(&s->unit->device,
+				"Detect jumbo payload: %02x %02x\n",
+				payload_quadlets, max_payload_quadlets);
+			s->packet_index = -1;
+			break;
+		}
+
 		handle_in_packet(s, payload_quadlets, buffer);
 	}
 
diff --git a/sound/firewire/amdtp.h b/sound/firewire/amdtp.h
index 8a03a91..26b9093 100644
--- a/sound/firewire/amdtp.h
+++ b/sound/firewire/amdtp.h
@@ -29,6 +29,9 @@
  *	packet is not continuous from an initial value.
  * @CIP_EMPTY_HAS_WRONG_DBC: Only for in-stream. The value of dbc in empty
  *	packet is wrong but the others are correct.
+ * @CIP_JUMBO_PAYLOAD: Only for in-stream. The number of data blocks in an
+ *	packet is larger than IEC 61883-6 defines. Current implementation
+ *	allows 5 times as large as IEC 61883-6 defines.
  */
 enum cip_flags {
 	CIP_NONBLOCKING		= 0x00,
@@ -40,6 +43,7 @@ enum cip_flags {
 	CIP_SKIP_DBC_ZERO_CHECK	= 0x20,
 	CIP_SKIP_INIT_DBC_CHECK	= 0x40,
 	CIP_EMPTY_HAS_WRONG_DBC	= 0x80,
+	CIP_JUMBO_PAYLOAD	= 0x100,
 };
 
 /**
diff --git a/sound/firewire/oxfw/oxfw-stream.c b/sound/firewire/oxfw/oxfw-stream.c
index e6757cd..873d40f 100644
--- a/sound/firewire/oxfw/oxfw-stream.c
+++ b/sound/firewire/oxfw/oxfw-stream.c
@@ -232,9 +232,15 @@ int snd_oxfw_stream_init_simplex(struct snd_oxfw *oxfw,
 		goto end;
 	}
 
-	/* OXFW starts to transmit packets with non-zero dbc. */
+	/*
+	 * OXFW starts to transmit packets with non-zero dbc.
+	 * OXFW postpone transferring packets till handling any asynchronous
+	 * packets. As a result, next isochronous packet includes more data
+	 * blocks than IEC 61883-6 defines.
+	 */
 	if (stream == &oxfw->tx_stream)
-		oxfw->tx_stream.flags |= CIP_SKIP_INIT_DBC_CHECK;
+		oxfw->tx_stream.flags |= CIP_SKIP_INIT_DBC_CHECK |
+					 CIP_JUMBO_PAYLOAD;
 end:
 	return err;
 }
-- 
2.1.4