utils: split helpers from bindings.c into utils.{c,h}

[mirror_lxcfs.git] / utils.c

#define __STDC_FORMAT_MACROS
#include <errno.h>
#include <fcntl.h>
#include <inttypes.h>
#include <sched.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

#include "config.h"
#include "macro.h"
#include "memory_utils.h"
#include "utils.h"

/*
 * append the given formatted string to *src.
 * src: a pointer to a char* in which to append the formatted string.
 * sz: the number of characters printed so far, minus trailing \0.
 * asz: the allocated size so far
 * format: string format. See printf for details.
 * ...: varargs. See printf for details.
 */
void must_strcat(char **src, size_t *sz, size_t *asz, const char *format, ...)
{
	char tmp[BUF_RESERVE_SIZE];
	va_list		args;

	va_start (args, format);
	int tmplen = vsnprintf(tmp, BUF_RESERVE_SIZE, format, args);
	va_end(args);

	if (!*src || tmplen + *sz + 1 >= *asz) {
		char *tmp;
		do {
			tmp = realloc(*src, *asz + BUF_RESERVE_SIZE);
		} while (!tmp);
		*src = tmp;
		*asz += BUF_RESERVE_SIZE;
	}
	memcpy((*src) +*sz , tmp, tmplen+1); /* include the \0 */
	*sz += tmplen;
}

/**
 * in_same_namespace - Check whether two processes are in the same namespace.
 * @pid1 - PID of the first process.
 * @pid2 - PID of the second process.
 * @ns   - Name of the namespace to check. Must correspond to one of the names
 *         for the namespaces as shown in /proc/<pid/ns/
 *
 * If the two processes are not in the same namespace returns an fd to the
 * namespace of the second process identified by @pid2. If the two processes are
 * in the same namespace returns -EINVAL, -1 if an error occurred.
 */
static int in_same_namespace(pid_t pid1, pid_t pid2, const char *ns)
{
	__do_close_prot_errno int ns_fd1 = -1, ns_fd2 = -1;
	int ret = -1;
	struct stat ns_st1, ns_st2;

	ns_fd1 = preserve_ns(pid1, ns);
	if (ns_fd1 < 0) {
		/* The kernel does not support this namespace. This is not an
		 * error.
		 */
		if (errno == ENOENT)
			return -EINVAL;

		return -1;
	}

	ns_fd2 = preserve_ns(pid2, ns);
	if (ns_fd2 < 0)
		return -1;

	ret = fstat(ns_fd1, &ns_st1);
	if (ret < 0)
		return -1;

	ret = fstat(ns_fd2, &ns_st2);
	if (ret < 0)
		return -1;

	/* processes are in the same namespace */
	if ((ns_st1.st_dev == ns_st2.st_dev) && (ns_st1.st_ino == ns_st2.st_ino))
		return -EINVAL;

	/* processes are in different namespaces */
	return move_fd(ns_fd2);
}

bool is_shared_pidns(pid_t pid)
{
	if (pid != 1)
		return false;

	if (in_same_namespace(pid, getpid(), "pid") == -EINVAL)
		return true;

	return false;
}

int preserve_ns(const int pid, const char *ns)
{
	int ret;
/* 5 /proc + 21 /int_as_str + 3 /ns + 20 /NS_NAME + 1 \0 */
#define __NS_PATH_LEN 50
	char path[__NS_PATH_LEN];

	/* This way we can use this function to also check whether namespaces
	 * are supported by the kernel by passing in the NULL or the empty
	 * string.
	 */
	ret = snprintf(path, __NS_PATH_LEN, "/proc/%d/ns%s%s", pid,
		       !ns || strcmp(ns, "") == 0 ? "" : "/",
		       !ns || strcmp(ns, "") == 0 ? "" : ns);
	if (ret < 0 || (size_t)ret >= __NS_PATH_LEN) {
		errno = EFBIG;
		return -1;
	}

	return open(path, O_RDONLY | O_CLOEXEC);
}