[PATCH v2][next] Bluetooth: hci_conn, hci_sync: Use __counted_by() in multiple structs and avoid -Wfamnae warnings

Gustavo A. R. Silva
2024-04-26T22:52:49Z

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 multiple on-stack definitions
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.

Notice that, due to the use of `__counted_by()` in `struct
hci_cp_le_create_cis`, the for loop in function `hci_cs_le_create_cis()`
had to be modified. Once the index `i`, through which `cp->cis[i]` is
accessed, falls in the interval [0, cp->num_cis), `cp->num_cis` cannot
be decremented all the way down to zero while accessing `cp->cis[]`:

net/bluetooth/hci_event.c:4310:
4310 for (i = 0; cp->num_cis; cp->num_cis--, i++) {
...
4314 handle = __le16_to_cpu(cp->cis[i].cis_handle);

otherwise, only half (one iteration before `cp->num_cis == i`) or half
plus one (one iteration before `cp->num_cis < i`) of the items in the
array will be accessed before running into an out-of-bounds issue. So,
in order to avoid this, set `cp->num_cis` to zero just after the for
loop.

Also, make use of `aux_num_cis` variable to update `cmd->num_cis` after
a `list_for_each_entry_rcu()` loop.

With these changes, fix the following warnings:
net/bluetooth/hci_sync.c:1239:56: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
net/bluetooth/hci_sync.c:1415:51: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
net/bluetooth/hci_sync.c:1731:51: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
net/bluetooth/hci_sync.c:6497:45: 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:
- Update `cmd->num_cis` after `list_for_each_entry_rcu()` loop.

v1:
- Link: https://lore.kernel.org/linux-hardening/ZiwqqZCa7PK9bzCX@neat/

include/net/bluetooth/hci.h | 8 ++--
net/bluetooth/hci_event.c | 3 +-
net/bluetooth/hci_sync.c | 84 +++++++++++++++----------------------
3 files changed, 40 insertions(+), 55 deletions(-)

diff --git a/include/net/bluetooth/hci.h b/include/net/bluetooth/hci.h
index fe23e862921d..c4c6b8810701 100644
--- a/include/net/bluetooth/hci.h
+++ b/include/net/bluetooth/hci.h
@@ -2026,7 +2026,7 @@ struct hci_cp_le_set_ext_adv_data {
__u8 operation;
__u8 frag_pref;
__u8 length;
- __u8 data[];
+ __u8 data[] __counted_by(length);
} __packed;

#define HCI_OP_LE_SET_EXT_SCAN_RSP_DATA 0x2038
@@ -2035,7 +2035,7 @@ struct hci_cp_le_set_ext_scan_rsp_data {
__u8 operation;
__u8 frag_pref;
__u8 length;
- __u8 data[];
+ __u8 data[] __counted_by(length);
} __packed;

#define HCI_OP_LE_SET_EXT_ADV_ENABLE 0x2039
@@ -2061,7 +2061,7 @@ struct hci_cp_le_set_per_adv_data {
__u8 handle;
__u8 operation;
__u8 length;
- __u8 data[];
+ __u8 data[] __counted_by(length);
} __packed;

#define HCI_OP_LE_SET_PER_ADV_ENABLE 0x2040
@@ -2162,7 +2162,7 @@ struct hci_cis {

struct hci_cp_le_create_cis {
__u8 num_cis;
- struct hci_cis cis[];
+ struct hci_cis cis[] __counted_by(num_cis);
} __packed;

#define HCI_OP_LE_REMOVE_CIG 0x2065
diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
index 9a38e155537e..9a7ca084302e 100644
--- a/net/bluetooth/hci_event.c
+++ b/net/bluetooth/hci_event.c
@@ -4307,7 +4307,7 @@ static void hci_cs_le_create_cis(struct hci_dev *hdev, u8 status)
hci_dev_lock(hdev);

/* Remove connection if command failed */
- for (i = 0; cp->num_cis; cp->num_cis--, i++) {
+ for (i = 0; i < cp->num_cis; i++) {
struct hci_conn *conn;
u16 handle;

@@ -4323,6 +4323,7 @@ static void hci_cs_le_create_cis(struct hci_dev *hdev, u8 status)
hci_conn_del(conn);
}
}
+ cp->num_cis = 0;

if (pending)
hci_le_create_cis_pending(hdev);
diff --git a/net/bluetooth/hci_sync.c b/net/bluetooth/hci_sync.c
index 9092b4d59545..6e15594d3565 100644
--- a/net/bluetooth/hci_sync.c
+++ b/net/bluetooth/hci_sync.c
@@ -1235,31 +1235,27 @@ int hci_setup_ext_adv_instance_sync(struct hci_dev *hdev, u8 instance)

static int hci_set_ext_scan_rsp_data_sync(struct hci_dev *hdev, u8 instance)
{
- struct {
- struct hci_cp_le_set_ext_scan_rsp_data cp;
- u8 data[HCI_MAX_EXT_AD_LENGTH];
- } pdu;
+ DEFINE_FLEX(struct hci_cp_le_set_ext_scan_rsp_data, pdu, data, length,
+ HCI_MAX_EXT_AD_LENGTH);
u8 len;
struct adv_info *adv = NULL;
int err;

- memset(&pdu, 0, sizeof(pdu));
-
if (instance) {
adv = hci_find_adv_instance(hdev, instance);
if (!adv || !adv->scan_rsp_changed)
return 0;
}

- len = eir_create_scan_rsp(hdev, instance, pdu.data);
+ len = eir_create_scan_rsp(hdev, instance, pdu->data);

- pdu.cp.handle = instance;
- pdu.cp.length = len;
- pdu.cp.operation = LE_SET_ADV_DATA_OP_COMPLETE;
- pdu.cp.frag_pref = LE_SET_ADV_DATA_NO_FRAG;
+ pdu->handle = instance;
+ pdu->length = len;
+ pdu->operation = LE_SET_ADV_DATA_OP_COMPLETE;
+ pdu->frag_pref = LE_SET_ADV_DATA_NO_FRAG;

err = __hci_cmd_sync_status(hdev, HCI_OP_LE_SET_EXT_SCAN_RSP_DATA,
- sizeof(pdu.cp) + len, &pdu.cp,
+ struct_size(pdu, data, len), pdu,
HCI_CMD_TIMEOUT);
if (err)
return err;
@@ -1267,7 +1263,7 @@ static int hci_set_ext_scan_rsp_data_sync(struct hci_dev *hdev, u8 instance)
if (adv) {
adv->scan_rsp_changed = false;
} else {
- memcpy(hdev->scan_rsp_data, pdu.data, len);
+ memcpy(hdev->scan_rsp_data, pdu->data, len);
hdev->scan_rsp_data_len = len;
}

@@ -1411,14 +1407,10 @@ static int hci_set_per_adv_params_sync(struct hci_dev *hdev, u8 instance,

static int hci_set_per_adv_data_sync(struct hci_dev *hdev, u8 instance)
{
- struct {
- struct hci_cp_le_set_per_adv_data cp;
- u8 data[HCI_MAX_PER_AD_LENGTH];
- } pdu;
+ DEFINE_FLEX(struct hci_cp_le_set_per_adv_data, pdu, data, length,
+ HCI_MAX_PER_AD_LENGTH);
u8 len;

- memset(&pdu, 0, sizeof(pdu));
-
if (instance) {
struct adv_info *adv = hci_find_adv_instance(hdev, instance);

@@ -1426,14 +1418,14 @@ static int hci_set_per_adv_data_sync(struct hci_dev *hdev, u8 instance)
return 0;
}

- len = eir_create_per_adv_data(hdev, instance, pdu.data);
+ len = eir_create_per_adv_data(hdev, instance, pdu->data);

- pdu.cp.length = len;
- pdu.cp.handle = instance;
- pdu.cp.operation = LE_SET_ADV_DATA_OP_COMPLETE;
+ pdu->length = len;
+ pdu->handle = instance;
+ pdu->operation = LE_SET_ADV_DATA_OP_COMPLETE;

return __hci_cmd_sync_status(hdev, HCI_OP_LE_SET_PER_ADV_DATA,
- sizeof(pdu.cp) + len, &pdu,
+ struct_size(pdu, data, len), pdu,
HCI_CMD_TIMEOUT);
}

@@ -1727,31 +1719,27 @@ int hci_le_terminate_big_sync(struct hci_dev *hdev, u8 handle, u8 reason)

static int hci_set_ext_adv_data_sync(struct hci_dev *hdev, u8 instance)
{
- struct {
- struct hci_cp_le_set_ext_adv_data cp;
- u8 data[HCI_MAX_EXT_AD_LENGTH];
- } pdu;
+ DEFINE_FLEX(struct hci_cp_le_set_ext_adv_data, pdu, data, length,
+ HCI_MAX_EXT_AD_LENGTH);
u8 len;
struct adv_info *adv = NULL;
int err;

- memset(&pdu, 0, sizeof(pdu));
-
if (instance) {
adv = hci_find_adv_instance(hdev, instance);
if (!adv || !adv->adv_data_changed)
return 0;
}

- len = eir_create_adv_data(hdev, instance, pdu.data);
+ len = eir_create_adv_data(hdev, instance, pdu->data);

- pdu.cp.length = len;
- pdu.cp.handle = instance;
- pdu.cp.operation = LE_SET_ADV_DATA_OP_COMPLETE;
- pdu.cp.frag_pref = LE_SET_ADV_DATA_NO_FRAG;
+ pdu->length = len;
+ pdu->handle = instance;
+ pdu->operation = LE_SET_ADV_DATA_OP_COMPLETE;
+ pdu->frag_pref = LE_SET_ADV_DATA_NO_FRAG;

err = __hci_cmd_sync_status(hdev, HCI_OP_LE_SET_EXT_ADV_DATA,
- sizeof(pdu.cp) + len, &pdu.cp,
+ struct_size(pdu, data, len), pdu,
HCI_CMD_TIMEOUT);
if (err)
return err;
@@ -1760,7 +1748,7 @@ static int hci_set_ext_adv_data_sync(struct hci_dev *hdev, u8 instance)
if (adv) {
adv->adv_data_changed = false;
} else {
- memcpy(hdev->adv_data, pdu.data, len);
+ memcpy(hdev->adv_data, pdu->data, len);
hdev->adv_data_len = len;
}

@@ -6496,10 +6484,8 @@ static int hci_le_create_conn_sync(struct hci_dev *hdev, void *data)

int hci_le_create_cis_sync(struct hci_dev *hdev)
{
- struct {
- struct hci_cp_le_create_cis cp;
- struct hci_cis cis[0x1f];
- } cmd;
+ DEFINE_FLEX(struct hci_cp_le_create_cis, cmd, cis, num_cis, 0x1f);
+ size_t aux_num_cis = 0;
struct hci_conn *conn;
u8 cig = BT_ISO_QOS_CIG_UNSET;

@@ -6526,8 +6512,6 @@ int hci_le_create_cis_sync(struct hci_dev *hdev)
* remains pending.
*/

- memset(&cmd, 0, sizeof(cmd));
-
hci_dev_lock(hdev);

rcu_read_lock();
@@ -6564,7 +6548,7 @@ int hci_le_create_cis_sync(struct hci_dev *hdev)
goto done;

list_for_each_entry_rcu(conn, &hdev->conn_hash.list, list) {
- struct hci_cis *cis = &cmd.cis[cmd.cp.num_cis];
+ struct hci_cis *cis = &cmd->cis[aux_num_cis];

if (hci_conn_check_create_cis(conn) ||
conn->iso_qos.ucast.cig != cig)
@@ -6573,25 +6557,25 @@ int hci_le_create_cis_sync(struct hci_dev *hdev)
set_bit(HCI_CONN_CREATE_CIS, &conn->flags);
cis->acl_handle = cpu_to_le16(conn->parent->handle);
cis->cis_handle = cpu_to_le16(conn->handle);
- cmd.cp.num_cis++;
+ aux_num_cis++;

- if (cmd.cp.num_cis >= ARRAY_SIZE(cmd.cis))
+ if (aux_num_cis >= 0x1f)
break;
}
+ cmd->num_cis = aux_num_cis;

done:
rcu_read_unlock();

hci_dev_unlock(hdev);

- if (!cmd.cp.num_cis)
+ if (!aux_num_cis)
return 0;

/* Wait for HCI_LE_CIS_Established */
return __hci_cmd_sync_status_sk(hdev, HCI_OP_LE_CREATE_CIS,
- sizeof(cmd.cp) + sizeof(cmd.cis[0]) *
- cmd.cp.num_cis, &cmd,
- HCI_EVT_LE_CIS_ESTABLISHED,
+ struct_size(cmd, cis, cmd->num_cis),
+ cmd, HCI_EVT_LE_CIS_ESTABLISHED,
conn->conn_timeout, NULL);
}

--
2.34.1