usbdevfs-drop-permissions.c
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#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <inttypes.h>
#include <unistd.h>
#include <linux/usbdevice_fs.h>
/* For building without an updated set of headers */
#ifndef USBDEVFS_DROP_PRIVILEGES
#define USBDEVFS_DROP_PRIVILEGES _IOW('U', 30, __u32)
#define USBDEVFS_CAP_DROP_PRIVILEGES 0x40
#endif
void drop_privileges(int fd, uint32_t mask)
{
int res;
res = ioctl(fd, USBDEVFS_DROP_PRIVILEGES, &mask);
if (res)
printf("ERROR: USBDEVFS_DROP_PRIVILEGES returned %d\n", res);
else
printf("OK: privileges dropped!\n");
}
void reset_device(int fd)
{
int res;
res = ioctl(fd, USBDEVFS_RESET);
if (!res)
printf("OK: USBDEVFS_RESET succeeded\n");
else
printf("ERROR: reset failed! (%d - %s)\n",
-res, strerror(-res));
}
void claim_some_intf(int fd)
{
int i, res;
for (i = 0; i < 4; i++) {
res = ioctl(fd, USBDEVFS_CLAIMINTERFACE, &i);
if (!res)
printf("OK: claimed if %d\n", i);
else
printf("ERROR claiming if %d (%d - %s)\n",
i, -res, strerror(-res));
}
}
int main(int argc, char *argv[])
{
uint32_t mask, caps;
int c, fd;
fd = open(argv[1], O_RDWR);
if (fd < 0) {
printf("Failed to open file\n");
goto err_fd;
}
/*
* check if dropping privileges is supported,
* bail on systems where the capability is not present
*/
ioctl(fd, USBDEVFS_GET_CAPABILITIES, &caps);
if (!(caps & USBDEVFS_CAP_DROP_PRIVILEGES)) {
printf("DROP_PRIVILEGES not supported\n");
goto err;
}
/*
* Drop privileges but keep the ability to claim all
* free interfaces (i.e., those not used by kernel drivers)
*/
drop_privileges(fd, -1U);
printf("Available options:\n"
"[0] Exit now\n"
"[1] Reset device. Should fail if device is in use\n"
"[2] Claim 4 interfaces. Should succeed where not in use\n"
"[3] Narrow interface permission mask\n"
"Which option shall I run?: ");
while (scanf("%d", &c) == 1) {
switch (c) {
case 0:
goto exit;
case 1:
reset_device(fd);
break;
case 2:
claim_some_intf(fd);
break;
case 3:
printf("Insert new mask: ");
scanf("%x", &mask);
drop_privileges(fd, mask);
break;
default:
printf("I don't recognize that\n");
}
printf("Which test shall I run next?: ");
}
exit:
close(fd);
return 0;
err:
close(fd);
err_fd:
return 1;
}