[alsa-devel] [PATCH 2/4] ALSA: control: delegate checking the length of data payload to each drivers

[Takashi Sakamoto]

In ioctl(2) for TLV feature of ALSA control interface, an argument is
a pointer to a data of 'struct snd_ctl_tlv' type in user space.
The first field of this structure is for numerical ID of control element
(numid), the second is for the length of the rest in byte unit (length).
The rest is data payload (tlv).

In current implementation, ALSA control core checks the length field
so that the lest is bigger than sizeof(unsigned int) * 2. This is due to
original design of this feature.

Originally, this feature is designed to allow each driver to handle
threshold level information. The rest of array stores the information.
The information is expected to be this formation:
 - type: e.g. SNDRV_CTL_TLVT_CONTAINER.
 - length: length of the rest
 - the rest: information fields

Against the original design, this feature can also be used to operate I/O.
In this case, the data field in 'struct snd_ctl_tlv' is not necessarily
the formation. Therefore, the check in control core is unreasonable.
Perhaps, there's a case to transfer just 1 byte by this feature.

This commit purges the check and delegate it to each drivers. Fortunately,
each implementation in drivers already check the length of payload.

Signed-off-by: Takashi Sakamoto <o-takashi at sakamocchi.jp>
---
 sound/core/control.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/sound/core/control.c b/sound/core/control.c
index 485963e..b6f4ebc 100644
--- a/sound/core/control.c
+++ b/sound/core/control.c
@@ -1438,8 +1438,6 @@ static int snd_ctl_tlv_ioctl(struct snd_ctl_file *file,
 
 	if (copy_from_user(&tlv, _tlv, sizeof(tlv)))
 		return -EFAULT;
-	if (tlv.length < sizeof(unsigned int) * 2)
-		return -EINVAL;
 	if (!tlv.numid)
 		return -EINVAL;
 	down_read(&card->controls_rwsem);
-- 
2.7.4