[PATCH 6.18 309/309] Bluetooth: L2CAP: Fix regressions caused by reusing ident

Greg Kroah-Hartman
2026-03-31T17:10:17Z

From: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

commit 761fb8ec8778f0caf2bba5a41e3cff1ea86974f3 upstream.

This attempt to fix regressions caused by reusing ident which apparently
is not handled well on certain stacks causing the stack to not respond to
requests, so instead of simple returning the first unallocated id this
stores the last used tx_ident and then attempt to use the next until all
available ids are exausted and then cycle starting over to 1.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=221120
Link: https://bugzilla.kernel.org/show_bug.cgi?id=221177
Fixes: 6c3ea155e5ee ("Bluetooth: L2CAP: Fix not tracking outstanding TX ident")
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Tested-by: Christian Eggers <ceggers@arri.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/net/bluetooth/l2cap.h | 1 +
net/bluetooth/l2cap_core.c | 29 ++++++++++++++++++++++++++---
2 files changed, 27 insertions(+), 3 deletions(-)

--- a/include/net/bluetooth/l2cap.h
+++ b/include/net/bluetooth/l2cap.h
@@ -658,6 +658,7 @@ struct l2cap_conn {
struct sk_buff *rx_skb;
__u32 rx_len;
struct ida tx_ida;
+ __u8 tx_ident;

struct sk_buff_head pending_rx;
struct work_struct pending_rx_work;
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -926,16 +926,39 @@ int l2cap_chan_check_security(struct l2c

static int l2cap_get_ident(struct l2cap_conn *conn)
{
+ u8 max;
+ int ident;
+
/* LE link does not support tools like l2ping so use the full range */
if (conn->hcon->type == LE_LINK)
- return ida_alloc_range(&conn->tx_ida, 1, 255, GFP_ATOMIC);
-
+ max = 255;
/* Get next available identificator.
* 1 - 128 are used by kernel.
* 129 - 199 are reserved.
* 200 - 254 are used by utilities like l2ping, etc.
*/
- return ida_alloc_range(&conn->tx_ida, 1, 128, GFP_ATOMIC);
+ else
+ max = 128;
+
+ /* Allocate ident using min as last used + 1 (cyclic) */
+ ident = ida_alloc_range(&conn->tx_ida, READ_ONCE(conn->tx_ident) + 1,
+ max, GFP_ATOMIC);
+ /* Force min 1 to start over */
+ if (ident <= 0) {
+ ident = ida_alloc_range(&conn->tx_ida, 1, max, GFP_ATOMIC);
+ if (ident <= 0) {
+ /* If all idents are in use, log an error, this is
+ * extremely unlikely to happen and would indicate a bug
+ * in the code that idents are not being freed properly.
+ */
+ BT_ERR("Unable to allocate ident: %d", ident);
+ return 0;
+ }
+ }
+
+ WRITE_ONCE(conn->tx_ident, ident);
+
+ return ident;
}

static void l2cap_send_acl(struct l2cap_conn *conn, struct sk_buff *skb,