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// Copyright 2015 CoreOS, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#define _GNU_SOURCE
#include <errno.h>
#include <pwd.h>
#include <sched.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include "user_lookup.h"
#define STACK_SIZE (64 * 1024)
/* This is all a bit copy-and-pasty from update-ssh-keys/authorized_keys_d,
* TODO(vc): refactor authorized_keys_d a bit so external packages can reuse
* the pieces duplicated here.
*/
typedef struct user_lookup_ctxt {
void *stack;
const char *name;
const char *root;
user_lookup_res_t *res;
int ret;
int err;
} user_lookup_ctxt_t;
static int user_lookup_fn(user_lookup_ctxt_t *ctxt) {
char buf[16 * 1024];
struct passwd p, *pptr;
if(chroot(ctxt->root) == -1) {
goto out_err;
}
if(getpwnam_r(ctxt->name, &p, buf, sizeof(buf), &pptr) != 0 || !pptr) {
goto out_err;
}
if(!(ctxt->res->name = strdup(p.pw_name))) {
goto out_err;
}
if(!(ctxt->res->home = strdup(p.pw_dir))) {
free(ctxt->res->name);
goto out_err;
}
ctxt->res->uid = p.pw_uid;
ctxt->res->gid = p.pw_gid;
return 0;
out_err:
ctxt->err = errno;
ctxt->ret = -1;
return 0;
}
/* user_lookup() looks up a user in a chroot.
* returns 0 and the results in res on success,
* res->name will be NULL if user doesn't exist.
* returns -1 on error.
*/
int user_lookup(const char *root, const char *name, user_lookup_res_t *res) {
user_lookup_ctxt_t ctxt = {
.root = root,
.name = name,
.res = res,
.ret = 0
};
int pid, ret = 0;
sigset_t allsigs, orig;
if(!(ctxt.stack = malloc(STACK_SIZE))) {
ret = -1;
goto out;
}
/* It's necessary to block all signals before cloning, so the child
* doesn't run any of the Go runtime's signal handlers.
*/
if((ret = sigemptyset(&orig)) == -1 ||
(ret = sigfillset(&allsigs)) == -1)
goto out_stack;
if((ret = sigprocmask(SIG_BLOCK, &allsigs, &orig)) == -1)
goto out_stack;
pid = clone((int(*)(void *))user_lookup_fn, ctxt.stack + STACK_SIZE,
CLONE_VM, &ctxt);
ret = sigprocmask(SIG_SETMASK, &orig, NULL);
if(pid != -1) {
if(waitpid(pid, NULL, __WCLONE) == -1 && errno != ECHILD) {
ret = -1;
goto out_stack;
}
} else {
ret = -1;
}
if(ret != -1) {
errno = ctxt.err;
ret = ctxt.ret;
}
out_stack:
free(ctxt.stack);
out:
return ret;
}
/* user_lookup_res_free() frees any memory allocated by a successful user_lookup(). */
void user_lookup_res_free(user_lookup_res_t *res) {
free(res->home);
free(res->name);
}
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