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#include "lock.hh"
#include "logging.hh"
#include "file-system.hh"
#include "globals.hh"
#include "pathlocks.hh"
#include <pwd.h>
#include <grp.h>
namespace nix {
#if __linux__
static std::vector<gid_t> get_group_list(const char *username, gid_t group_id)
{
std::vector<gid_t> gids;
gids.resize(32); // Initial guess
auto getgroupl_failed {[&] {
int ngroups = gids.size();
int err = getgrouplist(username, group_id, gids.data(), &ngroups);
gids.resize(ngroups);
return err == -1;
}};
// The first error means that the vector was not big enough.
// If it happens again, there is some different problem.
if (getgroupl_failed() && getgroupl_failed()) {
throw SysError("failed to get list of supplementary groups for '%s'", username);
}
return gids;
}
#endif
struct SimpleUserLock : UserLock
{
AutoCloseFD fdUserLock;
uid_t uid;
gid_t gid;
std::vector<gid_t> supplementaryGIDs;
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) {
#ifdef __APPLE__
#define APPLE_HINT "\n\nhint: this may be caused by an update to macOS Sequoia breaking existing Lix installations.\n" \
"See the macOS Sequoia page on the Lix wiki for detailed repair instructions: https://wiki.lix.systems/link/81"
#else
#define APPLE_HINT
#endif
throw Error("the user '%s' in the group '%s' does not exist" APPLE_HINT, i, settings.buildUsersGroup);
#undef APPLE_HINT
}
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 user. This is
* usually either empty or contains a group such as "kvm". */
// Finally, trim back the GID list to its real size.
for (auto gid : get_group_list(pw->pw_name, pw->pw_gid)) {
if (gid != lock->gid)
lock->supplementaryGIDs.push_back(gid);
}
#endif
return lock;
}
}
return nullptr;
}
};
struct AutoUserLock : UserLock
{
AutoCloseFD fdUserLock;
uid_t firstUid = 0;
gid_t firstGid = 0;
uid_t nrIds = 1;
uid_t getUID() override { assert(firstUid); return firstUid; }
gid_t getUIDCount() override { return nrIds; }
gid_t getGID() override { assert(firstGid); return firstGid; }
std::vector<gid_t> getSupplementaryGIDs() override { return {}; }
static std::unique_ptr<UserLock> acquire(uid_t nrIds, bool useUserNamespace)
{
#if !defined(__linux__)
useUserNamespace = false;
#endif
experimentalFeatureSettings.require(Xp::AutoAllocateUids);
assert(settings.startId > 0);
assert(settings.uidCount % maxIdsPerBuild == 0);
assert((uint64_t) settings.startId + (uint64_t) settings.uidCount <= std::numeric_limits<uid_t>::max());
assert(nrIds <= maxIdsPerBuild);
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 firstUid = settings.startId + i * maxIdsPerBuild;
auto pw = getpwuid(firstUid);
if (pw)
throw Error("auto-allocated UID %d clashes with existing user account '%s'", firstUid, pw->pw_name);
auto lock = std::make_unique<AutoUserLock>();
lock->fdUserLock = std::move(fd);
lock->firstUid = firstUid;
if (useUserNamespace)
lock->firstGid = firstUid;
else {
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);
lock->firstGid = gr->gr_gid;
}
lock->nrIds = nrIds;
return lock;
}
}
return nullptr;
}
};
std::unique_ptr<UserLock> acquireUserLock(uid_t nrIds, bool useUserNamespace)
{
if (settings.autoAllocateUids)
return AutoUserLock::acquire(nrIds, useUserNamespace);
else
return SimpleUserLock::acquire();
}
bool useBuildUsers()
{
#if __linux__
static bool b = (settings.buildUsersGroup != "" || settings.autoAllocateUids) && getuid() == 0;
return b;
#elif __APPLE__
static bool b = settings.buildUsersGroup != "" && getuid() == 0;
return b;
#else
return false;
#endif
}
}
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