From: Minseo Park Date: Sun, 15 Mar 2026 13:14:37 +0000 (+0900) Subject: Bluetooth: L2CAP: Fix stack-out-of-bounds read in l2cap_ecred_conn_req X-Git-Tag: v7.0-rc6~40^2~31^2~7 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=9d87cb22195b2c67405f5485d525190747ad5493;p=thirdparty%2Fkernel%2Flinux.git Bluetooth: L2CAP: Fix stack-out-of-bounds read in l2cap_ecred_conn_req Syzbot reported a KASAN stack-out-of-bounds read in l2cap_build_cmd() that is triggered by a malformed Enhanced Credit Based Connection Request. The vulnerability stems from l2cap_ecred_conn_req(). The function allocates a local stack buffer (`pdu`) designed to hold a maximum of 5 Source Channel IDs (SCIDs), totaling 18 bytes. When an attacker sends a request with more than 5 SCIDs, the function calculates `rsp_len` based on this unvalidated `cmd_len` before checking if the number of SCIDs exceeds L2CAP_ECRED_MAX_CID. If the SCID count is too high, the function correctly jumps to the `response` label to reject the packet, but `rsp_len` retains the attacker's oversized value. Consequently, l2cap_send_cmd() is instructed to read past the end of the 18-byte `pdu` buffer, triggering a KASAN panic. Fix this by moving the assignment of `rsp_len` to after the `num_scid` boundary check. If the packet is rejected, `rsp_len` will safely remain 0, and the error response will only read the 8-byte base header from the stack. Fixes: c28d2bff7044 ("Bluetooth: L2CAP: Fix result of L2CAP_ECRED_CONN_RSP when MTU is too short") Reported-by: syzbot+b7f3e7d9a596bf6a63e3@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=b7f3e7d9a596bf6a63e3 Tested-by: syzbot+b7f3e7d9a596bf6a63e3@syzkaller.appspotmail.com Signed-off-by: Minseo Park Signed-off-by: Luiz Augusto von Dentz --- diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c index 5deb6c4f1e41d..0882b5ac2ecca 100644 --- a/net/bluetooth/l2cap_core.c +++ b/net/bluetooth/l2cap_core.c @@ -5081,14 +5081,14 @@ static inline int l2cap_ecred_conn_req(struct l2cap_conn *conn, cmd_len -= sizeof(*req); num_scid = cmd_len / sizeof(u16); - /* Always respond with the same number of scids as in the request */ - rsp_len = cmd_len; - if (num_scid > L2CAP_ECRED_MAX_CID) { result = L2CAP_CR_LE_INVALID_PARAMS; goto response; } + /* Always respond with the same number of scids as in the request */ + rsp_len = cmd_len; + mtu = __le16_to_cpu(req->mtu); mps = __le16_to_cpu(req->mps);