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# -*- Autoconf -*-
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# SYNOPSIS
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#
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# AX_CHECK_USER_NAMESPACE
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#
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# DESCRIPTION
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#
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# This macro checks whether the local system supports Linux user namespaces.
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# If so, it calls AC_DEFINE(HAVE_USER_NAMESPACE).
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AC_DEFUN([AX_CHECK_USER_NAMESPACE],[dnl
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AC_CACHE_CHECK([whether user namespaces are supported],
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ax_cv_user_namespace,[
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AC_LANG_PUSH([C])
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AC_RUN_IFELSE([AC_LANG_SOURCE([[
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#define _GNU_SOURCE
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#include <fcntl.h>
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#include <sched.h>
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#include <signal.h>
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#include <stdio.h>
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#include <string.h>
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#include <sys/types.h>
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#include <sys/wait.h>
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int userfn(void *d) {
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usleep(100000); /* synchronize by sleep */
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return (getuid() != 0);
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}
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char userst[1024*1024];
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int main() {
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char buffer[1024];
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int rc, status, fd;
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pid_t child = clone(userfn, userst + 1024*1024, CLONE_NEWUSER|SIGCHLD, 0);
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if (child < 0) return 1;
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sprintf(buffer, "/proc/%d/uid_map", child);
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fd = open(buffer, O_CREAT|O_WRONLY|O_TRUNC, 0755);
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sprintf(buffer, "0 %d 1\n", getuid());
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write(fd, buffer, strlen(buffer));
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close(fd);
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rc = waitpid(child, &status, 0);
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if (rc <= 0) return 1;
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if (!WIFEXITED(status)) return 1;
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return WEXITSTATUS(status);
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}
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]])],[ax_cv_user_namespace=yes],[ax_cv_user_namespace=no],[ax_cv_user_namespace=no])
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AC_LANG_POP([C])
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])
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if test "$ax_cv_user_namespace" = yes; then
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AC_DEFINE([HAVE_USER_NAMESPACE],[1],[Whether user namespaces are available])
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fi
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]) # AX_CHECK_USER_NAMESPACE
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