[PATCH 12/13] hw/usb: Add U2F device check to passthru mode

[César Belley]

This patchs adds a check to verify that the device passed through the
hidraw property is a U2F device.

The check is done by ensuring that the first values of the report
descriptor (USAGE PAGE and USAGE) correspond to those of a U2F device.

Signed-off-by: César Belley <cesar.belley@lse.epita.fr>
---
 hw/usb/Makefile.objs  |  3 ++-
 hw/usb/u2f-passthru.c | 41 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/hw/usb/Makefile.objs b/hw/usb/Makefile.objs
index 7842a3175f..9e7e1f33a5 100644
--- a/hw/usb/Makefile.objs
+++ b/hw/usb/Makefile.objs
@@ -38,7 +38,8 @@ endif
 endif
 
 ifeq ($(CONFIG_USB_U2F),y)
-common-obj-y                          += u2f.o u2f-passthru.o
+common-obj-y                          += u2f.o
+common-obj-$(CONFIG_LINUX)            += u2f-passthru.o
 common-obj-$(CONFIG_U2F)              += u2f-emulated.o
 u2f-emulated.o-cflags = $(U2F_CFLAGS)
 u2f-emulated.o-libs = $(U2F_LIBS)
diff --git a/hw/usb/u2f-passthru.c b/hw/usb/u2f-passthru.c
index 106b5abf9e..f8771966c7 100644
--- a/hw/usb/u2f-passthru.c
+++ b/hw/usb/u2f-passthru.c
@@ -34,6 +34,12 @@
 
 #include "u2f.h"
 
+#ifdef CONFIG_LIBUDEV
+#include <libudev.h>
+#endif
+#include <linux/hidraw.h>
+#include <sys/ioctl.h>
+
 #define NONCE_SIZE 8
 #define BROADCAST_CID 0xFFFFFFFF
 #define TRANSACTION_TIMEOUT 120000
@@ -344,6 +350,34 @@ static void u2f_passthru_recv_from_guest(U2FKeyState *base,
     }
 }
 
+static bool u2f_passthru_is_u2f_device(int fd)
+{
+    int ret, rdesc_size;
+    struct hidraw_report_descriptor rdesc;
+    const uint8_t u2f_hid_report_desc_header[] = {
+        0x06, 0xd0, 0xf1, /* Usage Page (FIDO) */
+        0x09, 0x01,       /* Usage (FIDO) */
+    };
+
+    /* Get report descriptor size */
+    ret = ioctl(fd, HIDIOCGRDESCSIZE, &rdesc_size);
+    if (ret < 0 || rdesc_size < sizeof(u2f_hid_report_desc_header)) {
+        return false;
+    }
+
+    /* Get report descriptor */
+    memset(&rdesc, 0x0, sizeof(rdesc));
+    rdesc.size = rdesc_size;
+    ret = ioctl(fd, HIDIOCGRDESC, &rdesc);
+    if (ret < 0) {
+        return false;
+    }
+
+    /* Header bytes cover specific U2F rdesc values */
+    return memcmp(u2f_hid_report_desc_header, rdesc.value,
+                  sizeof(u2f_hid_report_desc_header)) == 0;
+}
+
 static void u2f_passthru_unrealize(U2FKeyState *base)
 {
     U2FPassthruState *key = PASSTHRU_U2F_KEY(base);
@@ -368,6 +402,13 @@ static void u2f_passthru_realize(U2FKeyState *base, Error 
**errp)
                    key->hidraw);
         return;
     }
+
+    if (!u2f_passthru_is_u2f_device(fd)) {
+        qemu_close(fd);
+        error_setg(errp, "%s: Passed hidraw does not represent "
+                   "a U2F HID device", TYPE_U2F_PASSTHRU);
+        return;
+    }
     key->hidraw_fd = fd;
     u2f_passthru_reset(key);
 }
-- 
2.28.0