zeroplus-logic-cube: move USB VID:PID check in scan before device access

Getting USB strings from faulty devices can be troublesome. Users report
segfaults when unrelated(!) devices get accessed during scan for certain
measurement devices.

Move the VID:PID check during scan before the USB string access. This
avoids access to unrelated devices.

Rephrase the check whether a USB device is a supported model. The
previous implementation's operation is questioned, the loop condition
looked suspicious.

Reported-By: Marek Antoniak <redacted> [the early check]

diff --git a/src/hardware/zeroplus-logic-cube/api.c b/src/hardware/zeroplus-logic-cube/api.c
index 9d15fe6c97c13ec7e915e3036861ba348e228f30..1fae2c8a8f541e00788e7d19cf03e69ff18e46b4 100644 (file)
--- a/src/hardware/zeroplus-logic-cube/api.c
+++ b/src/hardware/zeroplus-logic-cube/api.c
@@ -170,6 +170,7 @@ static GSList *scan(struct sr_dev_driver *di, GSList *options)
        libusb_device **devlist;
        GSList *devices;
        int ret, i, j;
+       const struct zp_model *check;
        char serial_num[64], connection_id[64];
 
        (void)options;
@@ -184,6 +185,30 @@ static GSList *scan(struct sr_dev_driver *di, GSList *options)
        for (i = 0; devlist[i]; i++) {
                libusb_get_device_descriptor(devlist[i], &des);
 
+               /*
+                * Check for expected VID:PID first as soon as we got
+                * the descriptor's content. This avoids access to flaky
+                * unrelated devices which trouble the application even
+                * if they are unrelated to measurement purposes.
+                *
+                * See https://sigrok.org/bugzilla/show_bug.cgi?id=1115
+                * and https://github.com/sigrokproject/libsigrok/pull/165
+                * for a discussion.
+                */
+               prof = NULL;
+               for (j = 0; zeroplus_models[j].vid; j++) {
+                       check = &zeroplus_models[j];
+                       if (des.idVendor != check->vid)
+                               continue;
+                       if (des.idProduct != check->pid)
+                               continue;
+                       prof = check;
+                       break;
+               }
+               if (!prof)
+                       continue;
+
+               /* Get the device's serial number from USB strings. */
                if ((ret = libusb_open(devlist[i], &hdl)) < 0)
                        continue;
 
@@ -202,16 +227,6 @@ static GSList *scan(struct sr_dev_driver *di, GSList *options)
                if (usb_get_port_path(devlist[i], connection_id, sizeof(connection_id)) < 0)
                        continue;
 
-               prof = NULL;
-               for (j = 0; j < zeroplus_models[j].vid; j++) {
-                       if (des.idVendor == zeroplus_models[j].vid &&
-                               des.idProduct == zeroplus_models[j].pid) {
-                               prof = &zeroplus_models[j];
-                       }
-               }
-
-               if (!prof)
-                       continue;
                sr_info("Found ZEROPLUS %s.", prof->model_name);
 
                sdi = g_malloc0(sizeof(struct sr_dev_inst));