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libreoffice-online/common/Seccomp.cpp
Ashod Nakashian 3109b99d49 wsd: sig: dump backtrace with USR2 
SIGUSR2 can now be used to dump the
stacktrace of coolwsd, forkit, and the
kit processes.

Also, support writing signalLog to files.
Although we write to stderr, we normalize
the interface used for signal logging and
allow for writing to any file descriptor.

Change-Id: If6366bb6ddbd9f8863baca52e4f65ebb468dc1f1
Signed-off-by: Ashod Nakashian <ashod.nakashian@collabora.co.uk>
2022-07-12 13:43:43 +01:00

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/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4; fill-column: 100 -*- */
/*
* 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>
#ifdef __linux__
#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/syscall.h>
#endif // __linux__
#include <sys/resource.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(__aarch64__)
# define AUDIT_ARCH_NR AUDIT_ARCH_AARCH64
# define SECCOMP_REG(_ctx, _reg) ((_ctx)->uc_mcontext.regs[_reg])
# define SECCOMP_SYSCALL(_ctx) SECCOMP_REG(_ctx, 8)
#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)
#elif defined(__powerpc64__)
# define AUDIT_ARCH_NR AUDIT_ARCH_PPC64
# define SECCOMP_REG(_ctx, _reg) ((_ctx)->uc_mcontext.regs->gpr[_reg])
# define SECCOMP_SYSCALL(_ctx) SECCOMP_REG(_ctx, 0)
#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);
SigUtil::signalLogOpen();
SigUtil::signalLogPrefix();
SigUtil::signalLog("SIGSYS trapped with code: ");
SigUtil::signalLogNumber(info->si_code);
SigUtil::signalLog(" and context ");
SigUtil::signalLogNumber(reinterpret_cast<size_t>(context));
SigUtil::signalLog("\n");
if (info->si_code != SYS_SECCOMP || !uctx)
return;
unsigned int syscall = SECCOMP_SYSCALL (uctx);
SigUtil::signalLogPrefix();
SigUtil::signalLog(" seccomp trapped signal, un-authorized sys-call: ");
SigUtil::signalLogNumber(syscall);
SigUtil::signalLog("\n");
SigUtil::dumpBacktrace();
SigUtil::signalLogClose();
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:
#if !defined(__NR_epoll_wait) && defined(__NR_epoll_pwait)
ACCEPT_SYSCALL(epoll_pwait),
#else
ACCEPT_SYSCALL(epoll_wait),
#endif
ACCEPT_SYSCALL(epoll_ctl),
#if !defined(__NR_epoll_create) && defined(__NR_epoll_create1)
ACCEPT_SYSCALL(epoll_create1),
#else
ACCEPT_SYSCALL(epoll_create),
#endif
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),
#ifdef __NR_uselib
KILL_SYSCALL(uselib),
#endif
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
#ifdef __NR_inotify_init
KILL_SYSCALL(inotify_init),
#endif
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 StringVector& tokens)
{
if (tokens.size() == 3 && tokens.equals(0, "setconfig"))
{
if (tokens.equals(1, "limit_virt_mem_mb"))
{
setRLimit(std::stoi(tokens[2]) * 1024 * 1024, RLIMIT_AS, "RLIMIT_AS", "bytes");
}
else if (tokens.equals(1, "limit_stack_mem_kb"))
{
setRLimit(std::stoi(tokens[2]) * 1024, RLIMIT_STACK, "RLIMIT_STACK", "bytes");
}
else if (tokens.equals(1, "limit_file_size_mb"))
{
setRLimit(std::stoi(tokens[2]) * 1024 * 1024, RLIMIT_FSIZE, "RLIMIT_FSIZE", "bytes");
}
else if (tokens.equals(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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