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#include "become_user.h"
#ifdef _linux_
#include <yql/essentials/utils/sys/linux_version.h>
#include <util/generic/yexception.h>
#include <util/system/user.h>
#include <memory>
#include <vector>
#include <errno.h>
#include <grp.h>
#include <pwd.h>
#include <unistd.h>
#include <sys/prctl.h>
#include <contrib/libs/libcap/include/sys/capability.h>
#include <contrib/libs/libcap/include/sys/securebits.h>
// strange, but sometimes we have to specify values manually
#define PR_CAP_AMBIENT 47
#define PR_CAP_AMBIENT_IS_SET 1
#define PR_CAP_AMBIENT_RAISE 2
#define PR_CAP_AMBIENT_LOWER 3
#define PR_CAP_AMBIENT_CLEAR_ALL 4
namespace NYql {
namespace {
void SetCapFlag(cap_t caps, cap_flag_t flag, cap_value_t value) {
if (cap_set_flag(caps, flag, 1, &value, CAP_SET) < 0) {
throw TSystemError() << "cap_set_flag() failed, flag = " << static_cast<int>(flag) << ", value = " << value;
}
}
void SetCapFlags(cap_t caps, cap_value_t value) {
SetCapFlag(caps, CAP_EFFECTIVE, value);
SetCapFlag(caps, CAP_PERMITTED, value);
SetCapFlag(caps, CAP_INHERITABLE, value);
}
void ClearAmbientCapFlags() {
// from man: PR_CAP_AMBIENT (since Linux 4.3)
if (IsLinuxKernelBelow4_3()) {
return;
}
if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_CLEAR_ALL, 0, 0, 0) < 0) {
throw TSystemError() << "prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_CLEAR_ALL, ....) failed";
}
}
void SetAmbientCapFlag(cap_value_t value) {
if (IsLinuxKernelBelow4_3()) {
return;
}
if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, value, 0, 0) < 0) {
throw TSystemError() << "prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, ....) failed, value = " << value;
}
}
void SetCapFlagsVector(const std::vector<cap_value_t>& flags) {
cap_t caps = cap_init();
std::unique_ptr<std::remove_reference_t<decltype(*caps)>, decltype(&cap_free)> capsHolder(caps, &cap_free);
if (!caps) {
throw TSystemError() << "cap_init() failed";
}
cap_clear(caps);
for (auto f : flags) {
SetCapFlags(caps, f);
}
if (cap_set_proc(caps) < 0) {
throw TSystemError() << "cap_set_proc() failed";
}
ClearAmbientCapFlags();
for (auto f : flags) {
SetAmbientCapFlag(f);
}
}
void EnsureCapFlagsVectorCannotBeRaised(const std::vector<cap_value_t>& flags) {
for (auto f : flags) {
try {
// one-by-one
SetCapFlagsVector({ f });
} catch (const TSystemError&) {
continue;
}
throw yexception() << "Cap flag " << f << " raised unexpectedly";
}
}
void DoBecomeUser(const char* username, const char* groupname) {
errno = 0;
passwd* pw = getpwnam(username);
if (pw == nullptr) {
if (errno == 0) {
ythrow yexception() << "unknown user: " << username;
} else {
ythrow TSystemError() << "can't get user info";
}
}
if (groupname == nullptr || strlen(groupname) == 0) {
groupname = username;
}
errno = 0;
group* gr = getgrnam(groupname);
if (gr == nullptr) {
if (errno == 0) {
ythrow yexception() << "unknown group: " << groupname;
} else {
ythrow TSystemError() << "can't get group info";
}
}
if (setgid(gr->gr_gid) == -1) {
ythrow TSystemError() << "can't change process group";
}
if (initgroups(username, gr->gr_gid) == -1) {
ythrow TSystemError() << "can't initgroups";
}
if (setuid(pw->pw_uid) == -1) {
ythrow TSystemError() << "can't change process user";
}
if (prctl(PR_SET_DUMPABLE, 1, 0, 0, 0) == -1) {
ythrow TSystemError() << "can't set dumpable flag for a process";
}
}
}
void BecomeUser(const TString& username, const TString& groupname) {
DoBecomeUser(username.data(), groupname.data());
}
void TurnOnBecomeUserAmbientCaps() {
SetCapFlagsVector({ CAP_SETUID, CAP_SETGID, CAP_SETPCAP, CAP_KILL });
if (prctl(PR_SET_SECUREBITS, SECBIT_NO_SETUID_FIXUP | SECBIT_NO_SETUID_FIXUP_LOCKED, 0, 0, 0) == -1) {
ythrow TSystemError() << "can't set secure bits for a process";
}
}
void TurnOffBecomeUserAbility() {
ClearAmbientCapFlags();
SetCapFlagsVector({});
EnsureCapFlagsVectorCannotBeRaised({ CAP_SETUID, CAP_SETGID, CAP_SETPCAP, CAP_KILL });
// ensure we cannot get root access back
if (setuid(0) != -1) {
ythrow TSystemError() << "unexpected switch to root in TurnOffBecomeUserAbility";
}
}
void DumpCaps(const TString& title) {
cap_t caps = cap_get_proc();
std::unique_ptr<std::remove_reference_t<decltype(*caps)>, decltype(&cap_free)> capsHolder(caps, &cap_free);
ssize_t size;
char* capsText = cap_to_text(caps, &size);
Cerr << title << ": current user: " << GetUsername() << ", proc caps: " << capsText << Endl;
cap_free(capsText);
}
void SendSignalOnParentThreadExit(int signo)
{
if (::prctl(PR_SET_PDEATHSIG, signo) == -1) {
ythrow TSystemError() << "Cannot set signal " << strsignal(signo) << " for parent death using prctl";
}
}
}
#endif
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