btusb_work() maps the number of active SCO links to USB alternate
settings through a three-entry lookup table when CVSD traffic uses
transparent voice settings. The lookup currently indexes alts[] with
data->sco_num - 1 without first constraining sco_num to the number of
available table entries.

While the table only defines alternate settings for up to three SCO
links, data->sco_num comes from hci_conn_num() and is used directly.
Cap the lookup to the last table entry before indexing it so the
driver keeps selecting the highest supported alternate setting without
reading past alts[].

Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
---
v2:
- rewrite the clamped SCO table index as an explicit 0-based clamp
  to avoid wraparound concerns raised in review

 drivers/bluetooth/btusb.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/bluetooth/btusb.c b/drivers/bluetooth/btusb.c
index a1c5eb993e47..5c535f3ab722 100644
--- a/drivers/bluetooth/btusb.c
+++ b/drivers/bluetooth/btusb.c
@@ -2376,8 +2376,11 @@ static void btusb_work(struct work_struct *work)
 		if (data->air_mode == HCI_NOTIFY_ENABLE_SCO_CVSD) {
 			if (hdev->voice_setting & 0x0020) {
 				static const int alts[3] = { 2, 4, 5 };
+				unsigned int sco_idx;
 
-				new_alts = alts[data->sco_num - 1];
+				sco_idx = min_t(unsigned int, data->sco_num - 1,
+						ARRAY_SIZE(alts) - 1);
+				new_alts = alts[sco_idx];
 			} else {
 				new_alts = data->sco_num;
 			}
-- 
2.50.1 (Apple Git-155)