[PATCH bluetooth] Bluetooth: l2cap: clear chan->ident on ECRED reconfiguration success

[Zhenghang Xiao <kipreyyy@gmail.com>]

l2cap_ecred_reconf_rsp() returns early on success without clearing
chan->ident. Every other L2CAP response handler (l2cap_ecred_conn_rsp,
l2cap_le_connect_rsp, l2cap_config_rsp) clears chan->ident after a
successful transaction to prevent the channel from matching subsequent
responses with the recycled ident value.

A remote attacker that completed a reconfiguration as the peer can
replay a failure response with the stale ident, causing the kernel to
match and destroy the already-established channel via
l2cap_chan_del(chan, ECONNRESET).

Clear chan->ident for all matching channels on success, and harden the
failure path by using l2cap_chan_hold_unless_zero() consistent with
other L2CAP handlers (l2cap_le_command_rej, __l2cap_get_chan_by_ident).

Fixes: 15f02b910562 ("Bluetooth: L2CAP: Add initial code for Enhanced Credit Based Mode")
Signed-off-by: Zhenghang Xiao <kipreyyy@gmail.com>
---
 net/bluetooth/l2cap_core.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index 7701528f1167..08c70caf24d4 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -5458,14 +5458,20 @@ static inline int l2cap_ecred_reconf_rsp(struct l2cap_conn *conn,
 
 	BT_DBG("result 0x%4.4x", result);
 
-	if (!result)
+	if (!result) {
+		list_for_each_entry(chan, &conn->chan_l, list) {
+			if (chan->ident == cmd->ident)
+				chan->ident = 0;
+		}
 		return 0;
+	}
 
 	list_for_each_entry_safe(chan, tmp, &conn->chan_l, list) {
 		if (chan->ident != cmd->ident)
 			continue;
 
-		l2cap_chan_hold(chan);
+		if (!l2cap_chan_hold_unless_zero(chan))
+			continue;
 		l2cap_chan_lock(chan);
 
 		l2cap_chan_del(chan, ECONNRESET);
-- 
2.50.1 (Apple Git-155)