[PATCH 2/4] Bluetooth: coredump: Fix btmon heap-buffer-overflow

The collected coredump data can exceed btmon's maximum packet size of
1490 bytes, But hci_devcd_dump() forwards the entire coredump data as an
HCI_DIAG_PKT without checking its size, causing below issue in btmon.

Why ?

For a monitor packet, its payload length @len in header may exceed
BTSNOOP_MAX_PACKET_SIZE, btmon uses it to access payload in @buf.
so cause heap-buffer-overflow.

Kernel:
include/net/bluetooth/hci_mon.h
struct hci_mon_hdr {
	__le16  opcode;
	__le16  index;
	__le16  len;
} __packed;

BlueZ:
src/shared/btsnoop.h
monitor/control.c
struct control_data {
	uint16_t channel;
	int fd;
	unsigned char buf[BTSNOOP_MAX_PACKET_SIZE];
	uint16_t offset;
};

Issue:
ERROR: AddressSanitizer: heap-buffer-overflow on address 0x51b00000065c at pc 0x7f50b987a029 bp 0x7ffde88dc8d0 sp 0x7ffde88dc088
READ of size 17916 at 0x51b00000065c thread T0
    #0 0x7f50b987a028 in write ../../../../src/libsanitizer/sanitizer_common/sanitizer_common_interceptors.inc:1096
    #1 0x5b4f3443ae3a in btsnoop_write ../src/shared/btsnoop.c:289
    #2 0x5b4f3429cbf0 in data_callback ../monitor/control.c:969
    #3 0x5b4f3444fa9d in mainloop_run ../src/shared/mainloop.c:104
    #4 0x5b4f34451da6 in mainloop_run_with_signal ../src/shared/mainloop-notify.c:196
    #5 0x5b4f342953fc in main ../monitor/main.c:303
    #6 0x7f50b8c2a1c9 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
    #7 0x7f50b8c2a28a in __libc_start_main_impl ../csu/libc-start.c:360
    #8 0x5b4f34295ed4 in _start (/usr/bin/btmon+0x29fed4) (BuildId: b41caafb24db693946c283eaea48112186863d2d)

Fix by forwarding the collected dump data as an HCI_DIAG_PKT only when
its size <= 1490.

Fixes: b257e02ecc46 ("HCI: coredump: Log devcd dumps into the monitor")
Signed-off-by: Zijun Hu <redacted>
---
 net/bluetooth/coredump.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/net/bluetooth/coredump.c b/net/bluetooth/coredump.c
index 71fc8dab4004..61b45ba58a65 100644
--- a/net/bluetooth/coredump.c
+++ b/net/bluetooth/coredump.c

@@ -250,36 +250,43 @@ static void hci_devcd_handle_pkt_pattern(struct hci_dev *hdev,
 	}
 
 	pattern = skb_pull_data(skb, sizeof(*pattern));
 
 	if (!hci_devcd_memset(hdev, pattern->pattern, pattern->len))
 		bt_dev_dbg(hdev, "Failed to set pattern");
 }
 
+/* Align with BlueZ's BTSNOOP_MAX_PACKET_SIZE. */
+#define HCI_DEVCD_DIAG_MAX_SIZE (1486 + 4)
+
 static void hci_devcd_dump(struct hci_dev *hdev)
 {
 	struct sk_buff *skb;
 	u32 size;
 
 	bt_dev_dbg(hdev, "state %s", hci_devcd_state_name(hdev->dump.state));
 
 	size = hdev->dump.tail - hdev->dump.head;
 
-	/* Send a copy to monitor as a diagnostic packet */
-	skb = bt_skb_alloc(size, GFP_ATOMIC);
-	if (skb) {
-		skb_put_data(skb, hdev->dump.head, size);
-		hci_recv_diag(hdev, skb);
+	if (size <= HCI_DEVCD_DIAG_MAX_SIZE) {
+		/* Send a copy to monitor as a diagnostic packet */
+		skb = bt_skb_alloc(size, GFP_ATOMIC);
+		if (skb) {
+			skb_put_data(skb, hdev->dump.head, size);
+			hci_recv_diag(hdev, skb);
+		}
 	}
 
 	/* Emit a devcoredump with the available data */
 	dev_coredumpv(&hdev->dev, hdev->dump.head, size, GFP_KERNEL);
 }
 
+#undef HCI_DEVCD_DIAG_MAX_SIZE
+
 static void hci_devcd_handle_pkt_complete(struct hci_dev *hdev,
 					  struct sk_buff *skb)
 {
 	u32 dump_size;
 
 	if (hdev->dump.state != HCI_DEVCOREDUMP_ACTIVE) {
 		DBG_UNEXPECTED_STATE();
 		return;

-- 
2.34.1