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/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4; fill-column: 100 -*- */
/*
* This file is part of the LibreOffice project.
*
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/.
*/
/*
* Code to lock-down the environment of the processes we run, to avoid
* exotic or un-necessary system calls to be used to break containment.
*/
#include <config.h>
#include "Seccomp.hpp"
#include <dlfcn.h>
#include <ftw.h>
#include <linux/audit.h>
#include <linux/filter.h>
#if DISABLE_SECCOMP == 0
#include <linux/seccomp.h>
#endif
#include <malloc.h>
#include <signal.h>
#include <sys/capability.h>
#include <sys/prctl.h>
#include <sys/resource.h>
#include <sys/syscall.h>
#include <sys/time.h>
#include <unistd.h>
#include <utime.h>
#include <common/Log.hpp>
#include <common/SigUtil.hpp>
#if DISABLE_SECCOMP == 0
#ifndef SYS_SECCOMP
# define SYS_SECCOMP 1
#endif
#if defined(__x86_64__)
# define AUDIT_ARCH_NR AUDIT_ARCH_X86_64
# define SECCOMP_REG(_ctx, _reg) ((_ctx)->uc_mcontext.gregs[(_reg)])
# define SECCOMP_SYSCALL(_ctx) SECCOMP_REG(_ctx, REG_RAX)
#elif defined(__arm__)
# define AUDIT_ARCH_NR AUDIT_ARCH_ARM
# define SECCOMP_REG(_ctx, _reg) ((_ctx)->uc_mcontext.arm_##_reg)
# define SECCOMP_SYSCALL(_ctx) SECCOMP_REG(_ctx, r7)
#else
# error "Platform does not support seccomp filtering yet - unsafe."
#endif
extern "C" {
static void handleSysSignal(int /* signal */,
siginfo_t *info,
void *context)
{
ucontext_t *uctx = static_cast<ucontext_t *>(context);
Log::signalLogPrefix();
Log::signalLog("SIGSYS trapped with code: ");
Log::signalLogNumber(info->si_code);
Log::signalLog(" and context ");
Log::signalLogNumber(reinterpret_cast<size_t>(context));
Log::signalLog("\n");
if (info->si_code != SYS_SECCOMP || !uctx)
return;
unsigned int syscall = SECCOMP_SYSCALL (uctx);
Log::signalLogPrefix();
Log::signalLog(" seccomp trapped signal, un-authorized sys-call: ");
Log::signalLogNumber(syscall);
Log::signalLog("\n");
SigUtil::dumpBacktrace();
Log::shutdown();
_exit(1);
}
} // extern "C"
#endif
namespace Seccomp {
bool lockdown(Type type)
{
(void)type; // so far just the kit.
#if DISABLE_SECCOMP == 0
#define ACCEPT_SYSCALL(name) \
BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_##name, 0, 1), \
BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW)
#define KILL_SYSCALL_FULL(fullname) \
BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, fullname, 0, 1), \
BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_TRAP)
#define KILL_SYSCALL(name) \
KILL_SYSCALL_FULL(__NR_##name)
struct sock_filter filterCode[] = {
// Check our architecture is correct.
BPF_STMT(BPF_LD+BPF_W+BPF_ABS, offsetof(struct seccomp_data, arch)),
BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, AUDIT_ARCH_NR, 1, 0),
BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_KILL),
// Load syscall number
BPF_STMT(BPF_LD+BPF_W+BPF_ABS, offsetof(struct seccomp_data, nr)),
// First white-list the syscalls we frequently use.
ACCEPT_SYSCALL(recvfrom),
ACCEPT_SYSCALL(write),
ACCEPT_SYSCALL(futex),
// glibc's 'poll' has to answer for this lot:
ACCEPT_SYSCALL(epoll_wait),
ACCEPT_SYSCALL(epoll_ctl),
ACCEPT_SYSCALL(epoll_create),
ACCEPT_SYSCALL(close),
ACCEPT_SYSCALL(nanosleep),
// Now block everything that we don't like the look of.
// FIXME: should we bother blocking calls that have early
// permission checks we don't meet ?
#if 0
// cf. eg. /usr/include/asm/unistd_64.h ...
KILL_SYSCALL(ioctl),
KILL_SYSCALL(mincore),
KILL_SYSCALL(shmget),
KILL_SYSCALL(shmat),
KILL_SYSCALL(shmctl),
#endif
KILL_SYSCALL(getitimer),
KILL_SYSCALL(setitimer),
KILL_SYSCALL(sendfile),
KILL_SYSCALL(listen), // server sockets
KILL_SYSCALL(accept), // server sockets
#if 0
KILL_SYSCALL(wait4),
#endif
KILL_SYSCALL(kill), // !
KILL_SYSCALL(shmctl),
KILL_SYSCALL(ptrace), // tracing
KILL_SYSCALL(capset),
KILL_SYSCALL(uselib),
KILL_SYSCALL(personality), // !
KILL_SYSCALL(vhangup),
#ifdef __NR_modify_ldt
KILL_SYSCALL(modify_ldt), // !
#endif
#ifdef __PNR_modify_ldt
KILL_SYSCALL_FULL(__PNR_modify_ldt), // !
#endif
KILL_SYSCALL(pivot_root), // !
KILL_SYSCALL(chroot),
KILL_SYSCALL(acct), // !
KILL_SYSCALL(sync), // I/O perf.
KILL_SYSCALL(mount),
KILL_SYSCALL(umount2),
KILL_SYSCALL(swapon),
KILL_SYSCALL(swapoff),
KILL_SYSCALL(reboot), // !
KILL_SYSCALL(sethostname),
KILL_SYSCALL(setdomainname),
KILL_SYSCALL(tkill),
KILL_SYSCALL(mbind), // vm bits
KILL_SYSCALL(set_mempolicy), // vm bits
KILL_SYSCALL(get_mempolicy), // vm bits
KILL_SYSCALL(kexec_load),
KILL_SYSCALL(add_key), // kernel keyring
KILL_SYSCALL(request_key), // kernel keyring
KILL_SYSCALL(keyctl), // kernel keyring
KILL_SYSCALL(inotify_init),
KILL_SYSCALL(inotify_add_watch),
KILL_SYSCALL(inotify_rm_watch),
KILL_SYSCALL(unshare),
KILL_SYSCALL(splice),
KILL_SYSCALL(tee),
KILL_SYSCALL(vmsplice), // vm bits
KILL_SYSCALL(move_pages), // vm bits
KILL_SYSCALL(accept4), // server sockets
KILL_SYSCALL(inotify_init1),
KILL_SYSCALL(perf_event_open), // profiling
KILL_SYSCALL(fanotify_init),
KILL_SYSCALL(fanotify_mark),
#ifdef __NR_seccomp
KILL_SYSCALL(seccomp), // no further fiddling
#endif
#ifdef __NR_bpf
KILL_SYSCALL(bpf), // no further fiddling
#endif
// allow the rest.
BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW)
};
struct sock_fprog filter = {
sizeof(filterCode)/sizeof(filterCode[0]), // length
filterCode
};
if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0))
{
LOG_ERR("Cannot turn off acquisition of new privileges for us & children");
return false;
}
if (prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &filter))
{
LOG_ERR("Failed to install seccomp syscall filter");
return false;
}
// Trap, log, and exit on failure
struct sigaction action;
sigemptyset(&action.sa_mask);
action.sa_flags = SA_SIGINFO;
action.sa_sigaction = handleSysSignal;
sigaction(SIGSYS, &action, nullptr);
LOG_TRC("Install seccomp filter successfully.");
return true;
#else // DISABLE_SECCOMP == 0
LOG_WRN("Warning: this binary was compiled with disabled seccomp-bpf.");
return true;
#endif // DISABLE_SECCOMP == 0
}
} // namespace Seccomp
namespace Rlimit {
void setRLimit(rlim_t confLim, int resource, const std::string &resourceText, const std::string &unitText)
{
rlim_t lim = confLim;
if (lim <= 0)
lim = RLIM_INFINITY;
const std::string limTextWithUnit((lim == RLIM_INFINITY) ? "unlimited" : std::to_string(lim) + " " + unitText);
if (resource != RLIMIT_FSIZE && resource != RLIMIT_NOFILE)
{
/* FIXME Currently the RLIMIT_FSIZE handling is non-ideal, and can
* lead to crashes of the kit processes due to not handling signal
* 25 gracefully. Let's disable for now before there's a more
* concrete plan.
* Similar issues with RLIMIT_NOFILE
*/
rlimit rlim = { lim, lim };
if (setrlimit(resource, &rlim) != 0)
LOG_SYS("Failed to set " << resourceText << " to " << limTextWithUnit << ".");
if (getrlimit(resource, &rlim) == 0)
{
const std::string setLimTextWithUnit((rlim.rlim_max == RLIM_INFINITY) ? "unlimited" : std::to_string(rlim.rlim_max) + " " + unitText);
LOG_INF(resourceText << " is " << setLimTextWithUnit << " after setting it to " << limTextWithUnit << ".");
}
else
LOG_SYS("Failed to get " << resourceText << ".");
}
else
LOG_INF("Ignored setting " << resourceText << " to " << limTextWithUnit << ".");
}
bool handleSetrlimitCommand(const std::vector<std::string>& tokens)
{
if (tokens.size() == 3 && tokens[0] == "setconfig")
{
if (tokens[1] == "limit_virt_mem_mb")
{
setRLimit(std::stoi(tokens[2]) * 1024 * 1024, RLIMIT_AS, "RLIMIT_AS", "bytes");
}
else if (tokens[1] == "limit_stack_mem_kb")
{
setRLimit(std::stoi(tokens[2]) * 1024, RLIMIT_STACK, "RLIMIT_STACK", "bytes");
}
else if (tokens[1] == "limit_file_size_mb")
{
setRLimit(std::stoi(tokens[2]) * 1024 * 1024, RLIMIT_FSIZE, "RLIMIT_FSIZE", "bytes");
}
else if (tokens[1] == "limit_num_open_files")
{
setRLimit(std::stoi(tokens[2]), RLIMIT_NOFILE, "RLIMIT_NOFILE", "files");
}
else
return false;
return true;
}
return false;
}
} // namespace Rlimit
/* vim:set shiftwidth=4 softtabstop=4 expandtab: */
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