ASoC: SOF: ipc3-control: Fix heap overflow in bytes_ext put/get

The ipc_control_data buffer is allocated as kzalloc(max_size), where
max_size covers the entire struct sof_ipc_ctrl_data including its
flexible array payload. However, the bounds checks in bytes_ext_put
and _bytes_ext_get compared user data lengths against max_size
directly, ignoring that cdata->data sits at an offset of
sizeof(struct sof_ipc_ctrl_data) bytes into the allocation.

This allowed writing up to sizeof(struct sof_ipc_ctrl_data) bytes past
the end of the heap buffer from unprivileged userspace via the ALSA TLV
kcontrol interface, and similarly allowed over-reading adjacent heap
data on the get path.

Fix all bounds checks to subtract sizeof(*cdata) from max_size so they
reflect the actual space available at the cdata->data offset. Also fix
the error-path restore in bytes_ext_put which wrote to cdata->data
instead of cdata, causing the same overflow.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@linux.intel.com>

Author: ujfalusi

sound/soc/sof/ipc3-control.c

@@ -389,9 +389,9 @@ static int sof_ipc3_bytes_ext_put(struct snd_sof_control *scontrol,
 	}
 
 	/* be->max is coming from topology */
-	if (header.length > scontrol->max_size) {
+	if (header.length > scontrol->max_size - sizeof(*cdata)) {
 		dev_err_ratelimited(scomp->dev, "Bytes data size %d exceeds max %zu\n",
-				    header.length, scontrol->max_size);
+				    header.length, scontrol->max_size - sizeof(*cdata));
 		return -EINVAL;
 	}
 
@@ -427,7 +427,7 @@ static int sof_ipc3_bytes_ext_put(struct snd_sof_control *scontrol,
 	}
 
 	/* be->max has been verified to be >= sizeof(struct sof_abi_hdr) */
-	if (cdata->data->size > scontrol->max_size - sizeof(struct sof_abi_hdr)) {
+	if (cdata->data->size > scontrol->max_size - sizeof(*cdata) - sizeof(struct sof_abi_hdr)) {
 		dev_err_ratelimited(scomp->dev, "Mismatch in ABI data size (truncated?)\n");
 		goto err_restore;
 	}
@@ -443,7 +443,7 @@ static int sof_ipc3_bytes_ext_put(struct snd_sof_control *scontrol,
 err_restore:
 	/* If we have an issue, we restore the old, valid bytes control data */
 	if (scontrol->old_ipc_control_data) {
-		memcpy(cdata->data, scontrol->old_ipc_control_data, scontrol->max_size);
+		memcpy(cdata, scontrol->old_ipc_control_data, scontrol->max_size);
 		kfree(scontrol->old_ipc_control_data);
 		scontrol->old_ipc_control_data = NULL;
 	}
@@ -482,10 +482,13 @@ static int _sof_ipc3_bytes_ext_get(struct snd_sof_control *scontrol,
 	}
 
 	/* check data size doesn't exceed max coming from topology */
-	if (cdata->data->size > scontrol->max_size - sizeof(struct sof_abi_hdr)) {
-		dev_err_ratelimited(scomp->dev, "User data size %d exceeds max size %zu\n",
+	if (cdata->data->size > scontrol->max_size - sizeof(*cdata) -
+				sizeof(struct sof_abi_hdr)) {
+		dev_err_ratelimited(scomp->dev,
+				    "User data size %d exceeds max size %zu\n",
 				    cdata->data->size,
-				    scontrol->max_size - sizeof(struct sof_abi_hdr));
+				    scontrol->max_size - sizeof(*cdata) -
+				    sizeof(struct sof_abi_hdr));
 		return -EINVAL;
 	}