In the Linux kernel, the following vulnerability has been resolved: Bluetooth: MGMT: reject...

In the Linux kernel, the following vulnerability has been resolved:

Bluetooth: MGMT: reject HCI_CMD_SYNC params_len above 255

mgmt_hci_cmd_sync() checks that the message length agrees with params_len but puts no upper bound on it. params_len is __le16 while the parameter length in the HCI command header is a u8:

struct hci_command_hdr {
	__le16	opcode;
	__u8	plen;
} __packed;

hci_cmd_sync_alloc() assigns one to the other:

hdr->plen = plen;

if (plen)
	skb_put_data(skb, param, plen);

so a params_len of 256 leaves plen at 0 while all 256 bytes are still appended. The frame handed to the driver then declares no parameters and carries 256 of them. On a length framed transport such as H:4 the controller takes the trailing bytes as the start of the next packet.

The mgmt socket MTU is HCI_MAX_FRAME_SIZE, so params_len can reach about 1KB this way. Commit 03f1700b9b4d ("Bluetooth: MGMT: reject malformed HCI_CMD_SYNC commands") only made params_len agree with the message length, a value that fits the message but not the header field is still accepted.

Reject params_len that does not fit the header field.