[PATCH v2][next] Bluetooth: hci_conn: Use __counted_by() in struct hci_cp_le_big_create_sync and avoid -Wfamnae warning

Gustavo A. R. Silva
2024-04-26T16:45:21Z

Prepare for the coming implementation by GCC and Clang of the
__counted_by attribute. Flexible array members annotated with
__counted_by can have their accesses bounds-checked at run-time
via CONFIG_UBSAN_BOUNDS (for array indexing) and CONFIG_FORTIFY_SOURCE
(for strcpy/memcpy-family functions).

Also, -Wflex-array-member-not-at-end is coming in GCC-14, and we are
getting ready to enable it globally.

So, use the `DEFINE_FLEX()` helper for an on-stack definition of
a flexible structure where the size of the flexible-array member
is known at compile-time, and refactor the rest of the code,
accordingly.

With these changes, fix the following warning:
net/bluetooth/hci_conn.c:2116:50: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

Link: https://github.com/KSPP/linux/issues/202
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
Changes in v2:
- Use `sizeof(*pdu) + num_bis` instead of `__struct_size(pdu)`

v1:
- Link: https://lore.kernel.org/linux-hardening/ZivYcpzZsc7aIFZ5@neat/

include/net/bluetooth/hci.h | 2 +-
net/bluetooth/hci_conn.c | 26 +++++++++++---------------
2 files changed, 12 insertions(+), 16 deletions(-)

diff --git a/include/net/bluetooth/hci.h b/include/net/bluetooth/hci.h
index 5c12761cbc0e..fe23e862921d 100644
--- a/include/net/bluetooth/hci.h
+++ b/include/net/bluetooth/hci.h
@@ -2216,7 +2216,7 @@ struct hci_cp_le_big_create_sync {
__u8 mse;
__le16 timeout;
__u8 num_bis;
- __u8 bis[];
+ __u8 bis[] __counted_by(num_bis);
} __packed;

#define HCI_OP_LE_BIG_TERM_SYNC 0x206c
diff --git a/net/bluetooth/hci_conn.c b/net/bluetooth/hci_conn.c
index 81166a5bc034..d6daf55f0307 100644
--- a/net/bluetooth/hci_conn.c
+++ b/net/bluetooth/hci_conn.c
@@ -2112,13 +2112,10 @@ int hci_le_big_create_sync(struct hci_dev *hdev, struct hci_conn *hcon,
struct bt_iso_qos *qos,
__u16 sync_handle, __u8 num_bis, __u8 bis[])
{
- struct _packed {
- struct hci_cp_le_big_create_sync cp;
- __u8 bis[0x11];
- } pdu;
+ DEFINE_FLEX(struct hci_cp_le_big_create_sync, pdu, bis, num_bis, 0x11);
int err;

- if (num_bis < 0x01 || num_bis > sizeof(pdu.bis))
+ if (num_bis < 0x01 || num_bis > pdu->num_bis)
return -EINVAL;

err = qos_set_big(hdev, qos);
@@ -2128,18 +2125,17 @@ int hci_le_big_create_sync(struct hci_dev *hdev, struct hci_conn *hcon,
if (hcon)
hcon->iso_qos.bcast.big = qos->bcast.big;

- memset(&pdu, 0, sizeof(pdu));
- pdu.cp.handle = qos->bcast.big;
- pdu.cp.sync_handle = cpu_to_le16(sync_handle);
- pdu.cp.encryption = qos->bcast.encryption;
- memcpy(pdu.cp.bcode, qos->bcast.bcode, sizeof(pdu.cp.bcode));
- pdu.cp.mse = qos->bcast.mse;
- pdu.cp.timeout = cpu_to_le16(qos->bcast.timeout);
- pdu.cp.num_bis = num_bis;
- memcpy(pdu.bis, bis, num_bis);
+ pdu->handle = qos->bcast.big;
+ pdu->sync_handle = cpu_to_le16(sync_handle);
+ pdu->encryption = qos->bcast.encryption;
+ memcpy(pdu->bcode, qos->bcast.bcode, sizeof(pdu->bcode));
+ pdu->mse = qos->bcast.mse;
+ pdu->timeout = cpu_to_le16(qos->bcast.timeout);
+ pdu->num_bis = num_bis;
+ memcpy(pdu->bis, bis, num_bis);

return hci_send_cmd(hdev, HCI_OP_LE_BIG_CREATE_SYNC,
- sizeof(pdu.cp) + num_bis, &pdu);
+ sizeof(*pdu) + num_bis, pdu);
}

static void create_big_complete(struct hci_dev *hdev, void *data, int err)
--
2.34.1