ALSA: firewire-lib: add buffer-over-run protection at receiving more data blocks than expected
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@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
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 @@
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;
}