Bluetooth: hci_conn, hci_sync: Use __counted_by() to avoid -Wfamnae warnings

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>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

1 files changed, 4 insertions, 4 deletions

diff --git a/include/net/bluetooth/hci.h b/include/net/bluetooth/hci.h
index 5c12761cbc0e..0b0ac7f06570 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