tools/perf/util/cap.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Capability utilities
   4  */
   5
   6 #include "cap.h"
   7 #include "debug.h"
   8 #include <errno.h>
   9 #include <string.h>
  10 #include <linux/capability.h>
  11 #include <sys/syscall.h>
  12 #include <unistd.h>
  13
  14 #define MAX_LINUX_CAPABILITY_U32S _LINUX_CAPABILITY_U32S_3
  15
  16 bool perf_cap__capable(int cap, bool *used_root)
  17 {
  18         struct __user_cap_header_struct header = {
  19                 .version = _LINUX_CAPABILITY_VERSION_3,
  20                 .pid = 0,
  21         };
  22         struct __user_cap_data_struct data[MAX_LINUX_CAPABILITY_U32S] = {};
  23         __u32 cap_val;
  24
  25         *used_root = false;
  26         while (syscall(SYS_capget, &header, &data[0]) == -1) {
  27                 /* Retry, first attempt has set the header.version correctly. */
  28                 if (errno == EINVAL && header.version != _LINUX_CAPABILITY_VERSION_3 &&
  29                     header.version == _LINUX_CAPABILITY_VERSION_1)
  30                         continue;
  31
  32                 pr_debug2("capget syscall failed (%s - %d) fall back on root check\n",
  33                           strerror(errno), errno);
  34                 *used_root = true;
  35                 return geteuid() == 0;
  36         }
  37
  38         /* Extract the relevant capability bit. */
  39         if (cap >= 32) {
  40                 if (header.version == _LINUX_CAPABILITY_VERSION_3) {
  41                         cap_val = data[1].effective;
  42                 } else {
  43                         /* Capability beyond 32 is requested but only 32 are supported. */
  44                         return false;
  45                 }
  46         } else {
  47                 cap_val = data[0].effective;
  48         }
  49         return (cap_val & (1 << (cap & 0x1f))) != 0;
  50 }