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