path: root/camel/camel-lock-helper.c

/* -*- Mode: C; tab-width: 8; indent-tabs-mode: t; c-basic-offset: 8 -*-
 *
 * Copyright (C) 2001 Ximian Inc.
 *
 * Authors: Michael Zucchi <notzed@ximian.com>
 *
 * This program is free software; you can redistribute it and/or 
 * modify it under the terms of the GNU General Public License as 
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
 * USA
 */

/* lock helper process */

#include <stdio.h>
#include <stdlib.h>

#include <errno.h>

#include <sys/time.h>
#include <sys/types.h>
#include <sys/stat.h>

#include <signal.h>

#include <unistd.h>
#include <fcntl.h>
#include <utime.h>

#include <time.h>

#define SETEUID_SAVES (1)

/* we try and include as little as possible */

#include "camel-lock-helper.h"
#include "camel-lock.h"

#define d(x)

/* keeps track of open locks */
struct _lock_info {
    struct _lock_info *next;
    uid_t uid;
    int id;
    int depth;
    time_t stamp;       /* when last updated */
    char path[1];
};

static int lock_id = 0;
static struct _lock_info *lock_info_list;
static uid_t lock_root_uid = -1;
static uid_t lock_real_uid = -1;

/* utility functions */

static int read_n(int fd, void *buffer, int inlen)
{
    char *p = buffer;
    int len, left = inlen;

    do {
        len = read(fd, p, left);
        if (len == -1) {
            if (errno != EINTR)
                return -1;
        } else {
            left -= len;
            p += len;
        }
    } while (left > 0 && len != 0);

    return inlen - left;
}

static int write_n(int fd, void *buffer, int inlen)
{
    char *p = buffer;
    int len, left = inlen;

    do {
        len = write(fd, p, left);
        if (len == -1) {
            if (errno != EINTR)
                return -1;
        } else {
            left -= len;
            p += len;
        }
    } while (left > 0);

    return inlen;
}

void
camel_exception_setv (CamelException *ex, ExceptionId id, const char *format, ...)
{
    ;
}

void
camel_exception_clear (CamelException *exception)
{
    ;
}

char *gettext (const char *msgid);

char *
gettext (const char *msgid)
{
    return NULL;
}

static int lock_path(const char *path, guint32 *lockid)
{
    struct _lock_info *info = NULL;
    int res = CAMEL_LOCK_HELPER_STATUS_OK;
    struct stat st;

    d(fprintf(stderr, "locking path '%s' id = %d\n", path, lock_id));

    /* check to see if we have it locked already, make the lock 'recursive' */
    /* we could also error i suppose, but why bother */
    info = lock_info_list;
    while (info) {
        if (!strcmp(info->path, path)) {
            info->depth++;
            return CAMEL_LOCK_HELPER_STATUS_OK;
        }
        info = info->next;
    }

    /* check we are allowed to lock it, we must own it, be able to write to it, and it has to exist */
    if (stat(path, &st) == -1
        || st.st_uid != getuid()
        || !S_ISREG(st.st_mode)
        || (st.st_mode & 0400) == 0) {
        return CAMEL_LOCK_HELPER_STATUS_INVALID;
    }

    info = malloc(sizeof(*info) + strlen(path));
    if (info == NULL) {
        res = CAMEL_LOCK_HELPER_STATUS_NOMEM;
        goto fail;
    }

    /* we try the real uid first, and if that fails, try the 'root id' */
    if (camel_lock_dot(path, NULL) == -1) {
#ifdef SETEUID_SAVES
        if (lock_real_uid != lock_root_uid) {
            if (seteuid(lock_root_uid) != -1) {
                if (camel_lock_dot(path, NULL) == -1) {
                    seteuid(lock_real_uid);
                    res = CAMEL_LOCK_HELPER_STATUS_SYSTEM;
                    goto fail;
                }
                seteuid(lock_real_uid);
            } else {
                res = CAMEL_LOCK_HELPER_STATUS_SYSTEM;
                goto fail;
            }
        } else {
            res = CAMEL_LOCK_HELPER_STATUS_SYSTEM;
            goto fail;
        }
#else
        res = CAMEL_LOCK_HELPER_STATUS_SYSTEM;
        goto fail;
#endif
    } else {
        info->uid = lock_real_uid;
    }

    strcpy(info->path, path);
    info->id = lock_id;
    info->depth = 1;
    info->next = lock_info_list;
    info->stamp = time(0);
    lock_info_list = info;

    if (lockid)
        *lockid = lock_id;

    lock_id++;

    d(fprintf(stderr, "lock ok\n"));

    return res;
fail:
    d(fprintf(stderr, "lock failed\n"));

    if (info)
        free(info);

    return res;
}

static int unlock_id(guint32 lockid)
{
    struct _lock_info *info, *p;

    d(fprintf(stderr, "unlocking id '%d'\n", lockid));

    p = (struct _lock_info *)&lock_info_list;
    info = p->next;
    while (info) {
        if (info->id == lockid) {
            d(fprintf(stderr, "found id %d path '%s'\n", lockid, info->path));
            info->depth--;
            if (info->depth <= 0) {
#ifdef SETEUID_SAVES
                if (info->uid != lock_real_uid) {
                    seteuid(lock_root_uid);
                    camel_unlock_dot(info->path);
                    seteuid(lock_real_uid);
                } else
#endif
                    camel_unlock_dot(info->path);

                p->next = info->next;
                free(info);
            }

            return CAMEL_LOCK_HELPER_STATUS_OK;
        }
        p = info;
        info = info->next;
    }

    d(fprintf(stderr, "unknown id asked to be unlocked %d\n", lockid));
    return CAMEL_LOCK_HELPER_STATUS_PROTOCOL;
}

static void lock_touch(const char *path)
{
    char *name;

    /* we could also check that we haven't had our lock stolen from us here */

    name = alloca(strlen(path) + 10);
    sprintf(name, "%s.lock", path);

    d(fprintf(stderr, "Updating lock %s\n", name));
    utime(name, NULL);
}

static void setup_process(void)
{
    struct sigaction sa;
    sigset_t sigset;
    
    /* ignore sigint/sigio */
    sa.sa_handler = SIG_IGN;
    sigemptyset (&sa.sa_mask);
    sa.sa_flags = 0;
    
    sigemptyset(&sigset);
    sigaddset(&sigset, SIGIO);
    sigaddset(&sigset, SIGINT);
    sigprocmask(SIG_UNBLOCK, &sigset, NULL);
    
    sigaction (SIGIO, &sa, NULL);
    sigaction (SIGINT, &sa, NULL);
    
    /* FIXME: add more sanity checks/setup here */

#ifdef SETEUID_SAVES
    /* here we change to the real user id, this is probably not particularly
       portable so may need configure checks */
    lock_real_uid = getuid();
    lock_root_uid = geteuid();
    if (lock_real_uid != lock_root_uid)
        seteuid(lock_real_uid);
#endif
}

int main(int argc, char **argv)
{
    struct _CamelLockHelperMsg msg;
    int len;
    int res;
    char *path;
    fd_set rset;
    struct timeval tv;
    struct _lock_info *info;

    setup_process();

    do {
        /* do a poll/etc, so we can refresh the .locks as required ... */
        FD_ZERO(&rset);
        FD_SET(STDIN_FILENO, &rset);

        /* check the minimum timeout we need to refresh the next oldest lock */
        if (lock_info_list) {
            time_t now = time(0);
            time_t left;
            time_t delay = CAMEL_DOT_LOCK_REFRESH;

            info = lock_info_list;
            while (info) {
                left = CAMEL_DOT_LOCK_REFRESH - (now - info->stamp);
                left = MAX(left, 0);
                delay = MIN(left, delay);
                info = info->next;
            }

            tv.tv_sec = delay;
            tv.tv_usec = 0;
        }
        
        d(fprintf(stderr, "lock helper waiting for input\n"));
        if (select(STDIN_FILENO+1, &rset, NULL, NULL, lock_info_list?&tv:NULL) == -1) {
            if (errno == EINTR)
                break;

            continue;
        }

        /* did we get a timeout?  scan for any locks that need updating */
        if (!FD_ISSET(STDIN_FILENO, &rset)) {
            time_t now = time(0);
            time_t left;

            d(fprintf(stderr, "Got a timeout, checking locks\n"));

            info = lock_info_list;
            while (info) {
                left = (now - info->stamp);
                if (left >= CAMEL_DOT_LOCK_REFRESH) {
                    lock_touch(info->path);
                    info->stamp = now;
                }
                info = info->next;
            }
            
            continue;
        }


        len = read_n(STDIN_FILENO, &msg, sizeof(msg));
        if (len == 0)
            break;

        res = CAMEL_LOCK_HELPER_STATUS_PROTOCOL;
        if (len == sizeof(msg) && msg.magic == CAMEL_LOCK_HELPER_MAGIC) {
            switch(msg.id) {
            case CAMEL_LOCK_HELPER_LOCK:
                res = CAMEL_LOCK_HELPER_STATUS_NOMEM;
                path = malloc(msg.data+1);
                if (path != NULL) {
                    res = CAMEL_LOCK_HELPER_STATUS_PROTOCOL;
                    len = read_n(STDIN_FILENO, path, msg.data);
                    if (len == msg.data) {
                        path[len] = 0;
                        res = lock_path(path, &msg.data);
                    }
                    free(path);
                }
                break;
            case CAMEL_LOCK_HELPER_UNLOCK:
                res = unlock_id(msg.data);
                break;
            }
        }
        d(fprintf(stderr, "returning result %d\n", res));
        msg.id = res;
        msg.magic = CAMEL_LOCK_HELPER_RETURN_MAGIC;
        write_n(STDOUT_FILENO, &msg, sizeof(msg));
    } while (1);

    d(fprintf(stderr, "parent exited, clsoing down remaining id's\n"));
    while (lock_info_list)
        unlock_id(lock_info_list->id);

    return 0;
}