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#include "lock.hh"
#include "globals.hh"
#include "pathlocks.hh"
#include "cgroup.hh"
#include <pwd.h>
#include <grp.h>
namespace nix {
struct SimpleUserLock : UserLock
{
AutoCloseFD fdUserLock;
uid_t uid;
gid_t gid;
std::vector<gid_t> supplementaryGIDs;
void kill() override
{
killUser(uid);
}
uid_t getUID() override { assert(uid); return uid; }
uid_t getUIDCount() override { return 1; }
gid_t getGID() override { assert(gid); return gid; }
std::vector<gid_t> getSupplementaryGIDs() override { return supplementaryGIDs; }
static std::unique_ptr<UserLock> acquire()
{
assert(settings.buildUsersGroup != "");
createDirs(settings.nixStateDir + "/userpool");
/* Get the members of the build-users-group. */
struct group * gr = getgrnam(settings.buildUsersGroup.get().c_str());
if (!gr)
throw Error("the group '%s' specified in 'build-users-group' does not exist", settings.buildUsersGroup);
/* Copy the result of getgrnam. */
Strings users;
for (char * * p = gr->gr_mem; *p; ++p) {
debug("found build user '%s'", *p);
users.push_back(*p);
}
if (users.empty())
throw Error("the build users group '%s' has no members", settings.buildUsersGroup);
/* Find a user account that isn't currently in use for another
build. */
for (auto & i : users) {
debug("trying user '%s'", i);
struct passwd * pw = getpwnam(i.c_str());
if (!pw)
throw Error("the user '%s' in the group '%s' does not exist", i, settings.buildUsersGroup);
auto fnUserLock = fmt("%s/userpool/%s", settings.nixStateDir,pw->pw_uid);
AutoCloseFD fd = open(fnUserLock.c_str(), O_RDWR | O_CREAT | O_CLOEXEC, 0600);
if (!fd)
throw SysError("opening user lock '%s'", fnUserLock);
if (lockFile(fd.get(), ltWrite, false)) {
auto lock = std::make_unique<SimpleUserLock>();
lock->fdUserLock = std::move(fd);
lock->uid = pw->pw_uid;
lock->gid = gr->gr_gid;
/* Sanity check... */
if (lock->uid == getuid() || lock->uid == geteuid())
throw Error("the Nix user should not be a member of '%s'", settings.buildUsersGroup);
#if __linux__
/* Get the list of supplementary groups of this build
user. This is usually either empty or contains a
group such as "kvm". */
int ngroups = 32; // arbitrary initial guess
lock->supplementaryGIDs.resize(ngroups);
int err = getgrouplist(
pw->pw_name, pw->pw_gid,
lock->supplementaryGIDs.data(),
&ngroups);
/* Our initial size of 32 wasn't sufficient, the
correct size has been stored in ngroups, so we try
again. */
if (err == -1) {
lock->supplementaryGIDs.resize(ngroups);
err = getgrouplist(
pw->pw_name, pw->pw_gid,
lock->supplementaryGIDs.data(),
&ngroups);
}
// If it failed once more, then something must be broken.
if (err == -1)
throw Error("failed to get list of supplementary groups for '%s'", pw->pw_name);
// Finally, trim back the GID list to its real size.
lock->supplementaryGIDs.resize(ngroups);
#endif
return lock;
}
}
return nullptr;
}
};
struct AutoUserLock : UserLock
{
AutoCloseFD fdUserLock;
uid_t firstUid = 0;
uid_t nrIds = 1;
#if __linux__
std::optional<Path> cgroup;
#endif
~AutoUserLock()
{
// Get rid of our cgroup, ignoring errors.
if (cgroup) rmdir(cgroup->c_str());
}
void kill() override
{
#if __linux__
if (cgroup) {
printError("KILL CGROUP %s", *cgroup);
destroyCgroup(*cgroup);
if (mkdir(cgroup->c_str(), 0755) == -1)
throw SysError("creating cgroup '%s'", *cgroup);
} else
#endif
{
assert(firstUid);
printError("KILL USER %d", firstUid);
killUser(firstUid);
}
}
uid_t getUID() override { assert(firstUid); return firstUid; }
gid_t getUIDCount() override { return nrIds; }
gid_t getGID() override
{
// We use the same GID ranges as for the UIDs.
assert(firstUid);
return firstUid;
}
std::vector<gid_t> getSupplementaryGIDs() override { return {}; }
static std::unique_ptr<UserLock> acquire(uid_t nrIds)
{
settings.requireExperimentalFeature(Xp::AutoAllocateUids);
assert(settings.startId > 0);
assert(settings.startId % maxIdsPerBuild == 0);
assert(settings.uidCount % maxIdsPerBuild == 0);
assert((uint64_t) settings.startId + (uint64_t) settings.uidCount <= std::numeric_limits<uid_t>::max());
assert(nrIds <= maxIdsPerBuild);
// FIXME: check whether the id range overlaps any known users
createDirs(settings.nixStateDir + "/userpool2");
size_t nrSlots = settings.uidCount / maxIdsPerBuild;
for (size_t i = 0; i < nrSlots; i++) {
debug("trying user slot '%d'", i);
createDirs(settings.nixStateDir + "/userpool2");
auto fnUserLock = fmt("%s/userpool2/slot-%d", settings.nixStateDir, i);
AutoCloseFD fd = open(fnUserLock.c_str(), O_RDWR | O_CREAT | O_CLOEXEC, 0600);
if (!fd)
throw SysError("opening user lock '%s'", fnUserLock);
if (lockFile(fd.get(), ltWrite, false)) {
auto s = drainFD(fd.get());
#if __linux__
if (s != "") {
/* Kill the old cgroup, to ensure there are no
processes left over from an interrupted build. */
destroyCgroup(s);
}
#endif
if (ftruncate(fd.get(), 0) == -1)
throw Error("truncating user lock");
auto lock = std::make_unique<AutoUserLock>();
lock->fdUserLock = std::move(fd);
lock->firstUid = settings.startId + i * maxIdsPerBuild;
lock->nrIds = nrIds;
if (nrIds > 1) {
auto ourCgroups = getCgroups("/proc/self/cgroup");
auto ourCgroup = ourCgroups[""];
if (ourCgroup == "")
throw Error("cannot determine cgroup name from /proc/self/cgroup");
auto ourCgroupPath = canonPath("/sys/fs/cgroup/" + ourCgroup);
printError("PARENT CGROUP = %s", ourCgroupPath);
if (!pathExists(ourCgroupPath))
throw Error("expected cgroup directory '%s'", ourCgroupPath);
lock->cgroup = fmt("%s/nix-build-%d", ourCgroupPath, lock->firstUid);
printError("CHILD CGROUP = %s", *lock->cgroup);
/* Record the cgroup in the lock file. This ensures that
if we subsequently get executed under a different parent
cgroup, we kill the previous cgroup first. */
writeFull(lock->fdUserLock.get(), *lock->cgroup);
}
return lock;
}
}
return nullptr;
}
#if __linux__
std::optional<Path> getCgroup() override { return cgroup; }
#endif
};
std::unique_ptr<UserLock> acquireUserLock(uid_t nrIds)
{
if (settings.autoAllocateUids)
return AutoUserLock::acquire(nrIds);
else
return SimpleUserLock::acquire();
}
bool useBuildUsers()
{
#if __linux__
static bool b = (settings.buildUsersGroup != "" || settings.startId.get() != 0) && getuid() == 0;
return b;
#elif __APPLE__
static bool b = settings.buildUsersGroup != "" && getuid() == 0;
return b;
#else
return false;
#endif
}
}
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