root/Documentation/usb/usbdevfs-drop-permissions.c

DEFINITIONS

1. drop_privileges
2. reset_device
3. claim_some_intf
4. main

   1 #include <sys/ioctl.h>
   2 #include <sys/types.h>
   3 #include <sys/stat.h>
   4 #include <fcntl.h>
   5 #include <stdio.h>
   6 #include <errno.h>
   7 #include <string.h>
   8 #include <inttypes.h>
   9 #include <unistd.h>
  10 
  11 #include <linux/usbdevice_fs.h>
  12 
  13 /* For building without an updated set of headers */
  14 #ifndef USBDEVFS_DROP_PRIVILEGES
  15 #define USBDEVFS_DROP_PRIVILEGES                _IOW('U', 30, __u32)
  16 #define USBDEVFS_CAP_DROP_PRIVILEGES            0x40
  17 #endif
  18 
  19 void drop_privileges(int fd, uint32_t mask)
  20 {
  21         int res;
  22 
  23         res = ioctl(fd, USBDEVFS_DROP_PRIVILEGES, &mask);
  24         if (res)
  25                 printf("ERROR: USBDEVFS_DROP_PRIVILEGES returned %d\n", res);
  26         else
  27                 printf("OK: privileges dropped!\n");
  28 }
  29 
  30 void reset_device(int fd)
  31 {
  32         int res;
  33 
  34         res = ioctl(fd, USBDEVFS_RESET);
  35         if (!res)
  36                 printf("OK: USBDEVFS_RESET succeeded\n");
  37         else
  38                 printf("ERROR: reset failed! (%d - %s)\n",
  39                        -res, strerror(-res));
  40 }
  41 
  42 void claim_some_intf(int fd)
  43 {
  44         int i, res;
  45 
  46         for (i = 0; i < 4; i++) {
  47                 res = ioctl(fd, USBDEVFS_CLAIMINTERFACE, &i);
  48                 if (!res)
  49                         printf("OK: claimed if %d\n", i);
  50                 else
  51                         printf("ERROR claiming if %d (%d - %s)\n",
  52                                i, -res, strerror(-res));
  53         }
  54 }
  55 
  56 int main(int argc, char *argv[])
  57 {
  58         uint32_t mask, caps;
  59         int c, fd;
  60 
  61         fd = open(argv[1], O_RDWR);
  62         if (fd < 0) {
  63                 printf("Failed to open file\n");
  64                 goto err_fd;
  65         }
  66 
  67         /*
  68          * check if dropping privileges is supported,
  69          * bail on systems where the capability is not present
  70          */
  71         ioctl(fd, USBDEVFS_GET_CAPABILITIES, &caps);
  72         if (!(caps & USBDEVFS_CAP_DROP_PRIVILEGES)) {
  73                 printf("DROP_PRIVILEGES not supported\n");
  74                 goto err;
  75         }
  76 
  77         /*
  78          * Drop privileges but keep the ability to claim all
  79          * free interfaces (i.e., those not used by kernel drivers)
  80          */
  81         drop_privileges(fd, -1U);
  82 
  83         printf("Available options:\n"
  84                 "[0] Exit now\n"
  85                 "[1] Reset device. Should fail if device is in use\n"
  86                 "[2] Claim 4 interfaces. Should succeed where not in use\n"
  87                 "[3] Narrow interface permission mask\n"
  88                 "Which option shall I run?: ");
  89 
  90         while (scanf("%d", &c) == 1) {
  91                 switch (c) {
  92                 case 0:
  93                         goto exit;
  94                 case 1:
  95                         reset_device(fd);
  96                         break;
  97                 case 2:
  98                         claim_some_intf(fd);
  99                         break;
 100                 case 3:
 101                         printf("Insert new mask: ");
 102                         scanf("%x", &mask);
 103                         drop_privileges(fd, mask);
 104                         break;
 105                 default:
 106                         printf("I don't recognize that\n");
 107                 }
 108 
 109                 printf("Which test shall I run next?: ");
 110         }
 111 
 112 exit:
 113         close(fd);
 114         return 0;
 115 
 116 err:
 117         close(fd);
 118 err_fd:
 119         return 1;
 120 }