286 Zeilen
6.8 KiB
C++
286 Zeilen
6.8 KiB
C++
#include <sys/prctl.h>
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#include <seccomp.h>
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#include <vector>
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#include <initializer_list>
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#include <string.h>
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#include <sched.h>
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#include <unistd.h>
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#include <fstream>
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <fcntl.h>
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#include <unistd.h>
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#include <string.h>
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#include <filesystem>
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#include <sys/mount.h>
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#include <sys/capability.h>
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#include "../logger.h"
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#include "../utils.h"
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#include "../random.h"
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#include "sandbox-linux.h"
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/* TODO: make a whitelist approach. So far we simply blacklist
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* obvious systemcalls. To whitelist, we need to analyse our
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* dependencies (http library, sqlite wrapper, sqlite lib etc.) */
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/* TODO: cleanup our sandboxing directory (unmount and delete folders) after exit */
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bool SandboxLinux::seccomp_blacklist(std::initializer_list<int> syscalls)
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{
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scmp_filter_ctx ctx;
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ctx = seccomp_init(SCMP_ACT_ALLOW);
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if(ctx == NULL)
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{
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Logger::error() << "failed to init seccomp_init";
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return false;
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}
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for(auto sc : syscalls)
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{
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if(seccomp_rule_add(ctx, SCMP_ACT_KILL_PROCESS, sc, 0) < 0)
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{
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Logger::error() << "Failed to add a seccomp rule";
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return false;
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}
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}
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bool success = seccomp_load(ctx) == 0;
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if(!success)
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{
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Logger::error() << "Failed to load seccomp filter";
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return false;
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}
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seccomp_release(ctx);
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return success;
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}
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bool SandboxLinux::bindMountPaths(std::string target_root, const std::vector<std::string> &paths)
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{
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for(const std::string &path : paths)
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{
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std::string chroot_target_path = target_root + path;
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if(std::filesystem::exists(chroot_target_path))
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{
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continue;
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}
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if(std::filesystem::is_regular_file(path))
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{
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std::fstream f1;
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f1.open(chroot_target_path, std::ios::out);
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f1.close();
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}
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else
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{
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std::error_code ec;
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//TODO: fails if the stuff already exists, but it shouldn't according to doc?
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if(!std::filesystem::create_directories(chroot_target_path, ec))
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{
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Logger::error() << "Error while trying to duplicate structure for sandbox. Dir creation failed. Path: " << chroot_target_path << " Error: " << ec.message();
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return false;
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}
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if(mount(path.c_str(), chroot_target_path.c_str(), NULL, MS_BIND, NULL) == -1)
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{
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Logger::error() << "Bind mount for " << path << " -> " << chroot_target_path << " failed! " << strerror(errno);
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return false;
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}
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}
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}
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return true;
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}
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bool SandboxLinux::isolateNamespaces(std::vector<std::string> fsPaths)
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{
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std::sort(fsPaths.begin(), fsPaths.end(), [](const std::string &a, const std::string &b){ return a.length() < b.length(); });
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auto current_uid = getuid();
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auto current_gid = getgid();
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if(unshare(CLONE_NEWUSER) == -1)
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{
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Logger::error() << "Failed to unshare user namespace: " << strerror(errno);
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return false;
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}
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std::fstream setgroups;
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setgroups.open("/proc/self/setgroups", std::ios::out | std::ios::app);
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setgroups << "deny";
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setgroups.flush();
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setgroups.close();
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std::fstream uid_map;
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uid_map.open("/proc/self/uid_map", std::ios::out | std::ios::app);
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uid_map << "0 " << current_uid << " 1\n";
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uid_map.flush();
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uid_map.close();
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std::fstream gid_map;
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gid_map.open("/proc/self/gid_map", std::ios::out);
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uid_map << "0 " << current_gid << " 1\n";
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gid_map.flush();
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gid_map.close();
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if(unshare(CLONE_NEWNS) == -1)
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{
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Logger::error() << "Failed to unshare mount namespace: " << strerror(errno);
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return false;
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}
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/*
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* TODO: breaks server.
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* TODO: fork?
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* if(unshare(CLONE_NEWPID) == -1)
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{
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Logger::error() << "Failed to unshare pid namespace: " << strerror(errno);
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return false;
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}*/
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//The purpose is to start with a clean sandbox dir.
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//We maybe could work with mkdirat, and check whether it exists alrady, to avoid
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//some attacks where an attacker gueses the dir, but in that case the system is already compromised
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//TODO: still, check, whether this is something we must consider here or not...
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Random random;
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std::string rootpath = "/tmp/qswiki_sandbox_" + random.getRandomHexString(10) + "/";
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if(!std::filesystem::create_directory(rootpath))
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{
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Logger::error() << "Failed to create chroot directory for sandbox";
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return false;
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}
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if(!bindMountPaths(rootpath, fsPaths ))
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{
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Logger::error() << "Bind mounting paths failed!";
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return false;
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}
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if(chroot(rootpath.c_str()) == -1)
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{
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Logger::error() << "chroot to sandbox failed!";
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return false;
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}
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if(chdir("/") == -1)
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{
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Logger::error() << "chdir to sandbox failed!";
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return false;
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}
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return true;
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}
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bool SandboxLinux::enableForInit()
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{
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umask(0027);
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//TODO. there is execv for SPARC. Sigh...
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if(!seccomp_blacklist({ SCMP_SYS(execveat), SCMP_SYS(execve) }))
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{
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Logger::error() << "Failed to install blacklisting seccomp filter";
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return false;
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}
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return true;
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}
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bool SandboxLinux::enablePreWorker(std::vector<std::string> fsPaths)
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{
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if(!isolateNamespaces(fsPaths))
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{
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Logger::error() << "Failed to isolate namespaces";
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return false;
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}
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return true;
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}
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bool SandboxLinux::supported()
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{
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std::fstream stream;
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stream.open("/proc/sys/kernel/unprivileged_userns_clone");
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if(stream.is_open())
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{
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std::string str;
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stream >> str;
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if(str[0] == '0')
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{
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Logger::error() << "Please write '1' to /proc/sys/kernel/unprivileged_userns_clone in order to enable sandboxing support on this system";
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return false;
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}
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}
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return true;
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}
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bool SandboxLinux::enableForWorker()
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{
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int cap = 0;
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int res = 0;
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while((res = prctl(PR_CAPBSET_DROP, cap++, 0, 0, 0)) == 0);
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if(res == -1 && errno != EINVAL)
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{
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Logger::error() << "Failed to drop the capability bounding set!";
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return false;
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}
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__user_cap_header_struct h = { 0 };
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h.pid = 0;
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h.version = _LINUX_CAPABILITY_VERSION_3;
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__user_cap_data_struct drop[2];
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drop[0].effective = 0;
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drop[0].permitted = 0;
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drop[0].inheritable = 0;
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drop[1].effective = 0;
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drop[1].permitted = 0;
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drop[1].inheritable = 0;
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if(capset(&h, drop) == -1)
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{
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Logger::error() << "Failed to drop capabilities: " << strerror(errno);
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return false;
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}
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/* TODO: as said, a whitelist approach is better. As such, this list is bound to be incomplete in the
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* sense that more could be listed here and some critical ones are probably missing */
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if(! seccomp_blacklist({
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SCMP_SYS(setuid),
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SCMP_SYS(setuid32),
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SCMP_SYS(connect),
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SCMP_SYS(chroot),
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SCMP_SYS(pivot_root),
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SCMP_SYS(mount),
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SCMP_SYS(setns),
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SCMP_SYS(unshare),
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SCMP_SYS(ptrace),
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SCMP_SYS(personality)
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}))
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{
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Logger::error() << "Sandbox: Activation of seccomp blacklist failed!";
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return false;
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}
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if(prctl(PR_SET_DUMPABLE, 0) == -1)
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{
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Logger::error() << "prctl: PR_SET_DUMPABLE failed";
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return false;
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}
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if(prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) == -1)
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{
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Logger::error() << "prctl: PR_SET_NO_NEW_PRIVS failed: " << strerror(errno);
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return false;
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}
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if(! seccomp_blacklist({ SCMP_SYS(prctl) }))
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{
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Logger::error() << "Sandbox: Activation of seccomp blacklist failed!";
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return false;
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}
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return true;
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}
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