port/rt/pos4obj.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright (c) 1993, 2010, Oracle and/or its affiliates. All rights reserved.
 */

#include "lint.h"
#include "mtlib.h"
#include <sys/types.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <unistd.h>
#include <stdlib.h>
#include <limits.h>
#include <pthread.h>
#include <thread.h>
#include <string.h>
#include <dirent.h>
#include <stdio.h>
#include <dlfcn.h>
#include <atomic.h>
#include <md5.h>
#include "pos4obj.h"

#define HASHSTRLEN  32

static  char    *__pos4obj_name(const char *, const char *);
static  void    __pos4obj_md5toa(unsigned char *, unsigned char *);
static  void    __pos4obj_clean(char *);

static  char    objroot[] = "/tmp/";
static  long int    name_max = 0;

int
__open_nc(const char *path, int oflag, mode_t mode)
{
    int     cancel_state;
    int     val;

    /*
     * Ensure path is not a symlink to somewhere else. This provides
     * a modest amount of protection against easy security attacks.
     * Also, set the close-on-exec flag atomically on open().
     */

    (void) pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cancel_state);
    val = open64(path, oflag | O_NOFOLLOW | O_CLOEXEC, mode);
    (void) pthread_setcancelstate(cancel_state, NULL);

    return (val);
}

int
__close_nc(int fildes)
{
    int cancel_state;
    int val;

    (void) pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cancel_state);
    val = close(fildes);
    (void) pthread_setcancelstate(cancel_state, NULL);

    return (val);
}

/*
 * This is to avoid loading libmd.so.1 unless we absolutely have to.
 */
typedef void (*md5_calc_t)(unsigned char *, unsigned char *, unsigned int);
static md5_calc_t real_md5_calc = NULL;
static mutex_t md5_lock = DEFAULTMUTEX;

static void
load_md5_calc(void)
{
    void *md5_handle = dlopen("libmd.so.1", RTLD_LAZY);
    md5_calc_t md5_calc = (md5_handle == NULL)? NULL :
        (md5_calc_t)dlsym(md5_handle, "md5_calc");

    lmutex_lock(&md5_lock);
    if (real_md5_calc == NULL) {
        if (md5_calc == NULL)
            real_md5_calc = (md5_calc_t)(-1);
        else {
            real_md5_calc = md5_calc;
            md5_handle = NULL;  /* don't dlclose it */
        }
        membar_producer();
    }
    lmutex_unlock(&md5_lock);

    if (md5_handle)
        (void) dlclose(md5_handle);
}

static char *
__pos4obj_name(const char *path, const char *type)
{
    int shortpath = 1;
    int olderrno;
    size_t  len;
    char    *dfile;
    unsigned char   hashbuf[HASHSTRLEN + 1];
    unsigned char   md5_digest[MD5_DIGEST_LENGTH];

    /*
     * If the path is path_max - strlen(type) characters or less,
     * the name of the file to use will be the path prefixed by
     * the type.
     *
     * In the special case where the path is longer than
     * path_max - strlen(type) characters, we create a string based on the
     * MD5 hash of the path. We prefix that string with a '.' to
     * make it obscure, and create a directory in objroot with
     * that name. In that directory, we create a directory named
     * after the type of object requested.  Inside the type
     * directory, the filename will be the path of the object. This
     * prevents collisions in all namespaces.
     *
     * Example:
     * Let objroot = "/tmp/", path = "/<longpath>", and type = ".MQD"
     * Let the MD5 hash of "<longpath>" = "<hash>"
     *
     * The desired file is /tmp/.<hash>/.MQD/<longpath>
     */

    /*
     * Do not include the leading '/' in the path length.
     * Assumes __pos4obj_check(path) has already been called.
     */
    if ((strlen(path) - 1) > (name_max - strlen(type)))
        shortpath = 0;

    if (shortpath) {
        /*
         * strlen(path) includes leading slash as space for NUL.
         */
        len = strlen(objroot) + strlen(type) + strlen(path);
    } else {
        /*
         * Long path name. Add 3 for extra '/', '.' and '\0'
         */
        len = strlen(objroot) + HASHSTRLEN + strlen(type) +
            strlen(path) + 3;
    }

    if ((dfile = malloc(len)) == NULL)
        return (NULL);

    (void) memset(dfile, 0, len);
    (void) strcpy(dfile, objroot);

    if (shortpath) {
        (void) strcat(dfile, type);
        (void) strcat(dfile, path + 1);
        return (dfile);
    }

    /*
     * If we can successfully load it, call md5_calc().
     * Otherwise, (this "can't happen") return NULL.
     */
    if (real_md5_calc == NULL)
        load_md5_calc();
    if (real_md5_calc == (md5_calc_t)(-1)) {
        free(dfile);
        return (NULL);
    }

    real_md5_calc(md5_digest, (unsigned char *)path + 1, strlen(path + 1));
    __pos4obj_md5toa(hashbuf, md5_digest);
    (void) strcat(dfile, ".");
    (void) strcat(dfile, (const char *)hashbuf);

    /*
     * Errno must be preserved across the following calls to
     * mkdir.  This needs to be done to prevent incorrect error
     * reporting in certain cases. When we attempt to open a
     * non-existent object without the O_CREAT flag, it will
     * always create a lock file first.  The lock file is created
     * and then the open is attempted, but fails with ENOENT. The
     * lock file is then destroyed. In the following code path, we
     * are finding the absolute path to the lock file after
     * already having attempted the open (which set errno to
     * ENOENT). The following calls to mkdir will return -1 and
     * set errno to EEXIST, since the hash and type directories
     * were created when the lock file was created. The correct
     * errno is the ENOENT from the attempted open of the desired
     * object.
     */
    olderrno = errno;

    /*
     * Create hash directory. Use 777 permissions so everyone can use it.
     */
    if (mkdir(dfile, S_IRWXU|S_IRWXG|S_IRWXO) == 0) {
        if (chmod(dfile, S_IRWXU|S_IRWXG|S_IRWXO) == -1) {
            free(dfile);
            return (NULL);
        }
    } else {
        if (errno != EEXIST) {
            free(dfile);
            return (NULL);
        }
    }

    (void) strcat(dfile, "/");
    (void) strcat(dfile, type);

    /*
     * Create directory for requested type. Use 777 perms so everyone
     * can use it.
     */
    if (mkdir(dfile, S_IRWXU|S_IRWXG|S_IRWXO) == 0) {
        if (chmod(dfile, S_IRWXU|S_IRWXG|S_IRWXO) == -1) {
            free(dfile);
            return (NULL);
        }
    } else {
        if (errno != EEXIST) {
            free(dfile);
            return (NULL);
        }
    }

    errno = olderrno;
    (void) strcat(dfile, path);
    return (dfile);
}

/*
 * Takes a 128-bit MD5 digest and transforms to a sequence of 32 ASCII
 * characters. Output is the hexadecimal representation of the digest.
 *
 * The output buffer must be at least HASHSTRLEN + 1 characters
 * long.  HASHSTRLEN is the size of the MD5 digest (128 bits)
 * divided by the number of bits used per char of output (4). The
 * extra character at the end is for the NUL terminating character.
 */

static void
__pos4obj_md5toa(unsigned char *dest, unsigned char *src)
{
    int i;
    uint32_t *p;

    /* LINTED pointer cast may result in improper alignment */
    p = (uint32_t *)src;

    for (i = 0; i < (MD5_DIGEST_LENGTH / 4); i++)
        (void) snprintf((char *)dest + (i * 8), 9, "%.8x", *p++);

    dest[HASHSTRLEN] = '\0';
}

/*
 * This open function assume that there is no simultaneous
 * open/unlink operation is going on. The caller is supposed
 * to ensure that both open in O_CREAT mode happen atomically.
 * It returns the crflag as 1 if file is created else 0.
 */
int
__pos4obj_open(const char *name, char *type, int oflag,
        mode_t mode, int *crflag)
{
    int fd;
    char *dfile;

    errno = 0;
    *crflag = 0;

    if ((dfile = __pos4obj_name(name, type)) == NULL) {
        return (-1);
    }

    if (!(oflag & O_CREAT)) {
        if ((fd = __open_nc(dfile, oflag, mode)) == -1)
            __pos4obj_clean(dfile);

        free(dfile);
        return (fd);
    }

    /*
     * We need to make sure that crflag is set iff we actually create
     * the file.  We do this by or'ing in O_EXCL, and attempting an
     * open.  If that fails with an EEXIST, and O_EXCL wasn't specified
     * by the caller, then the file seems to exist;  we'll try an
     * open with O_CREAT cleared.  If that succeeds, then the file
     * did indeed exist.  If that fails with an ENOENT, however, the
     * file was removed between the opens;  we need to take another
     * lap.
     */
    for (;;) {
        if ((fd = __open_nc(dfile, (oflag | O_EXCL), mode)) == -1) {
            if (errno == EEXIST && !(oflag & O_EXCL)) {
                fd = __open_nc(dfile, oflag & ~O_CREAT, mode);

                if (fd == -1 && errno == ENOENT)
                    continue;
                break;
            }
        } else {
            *crflag = 1;
        }
        break;
    }

    free(dfile);
    return (fd);
}


int
__pos4obj_unlink(const char *name, const char *type)
{
    int err;
    char    *dfile;

    if ((dfile = __pos4obj_name(name, type)) == NULL) {
        return (-1);
    }

    err = unlink(dfile);

    __pos4obj_clean(dfile);

    free(dfile);

    return (err);
}

/*
 * This function opens the lock file for each named object
 * the presence of this file in the file system is the lock
 */
int
__pos4obj_lock(const char *name, const char *ltype)
{
    char    *dfile;
    int fd;
    int limit = 64;

    if ((dfile = __pos4obj_name(name, ltype)) == NULL) {
        return (-1);
    }

    while (limit-- > 0) {
        if ((fd = __open_nc(dfile, O_RDWR | O_CREAT | O_EXCL, 0666))
            < 0) {
            if (errno != EEXIST)
                break;
            (void) sleep(1);
            continue;
        }

        (void) __close_nc(fd);
        free(dfile);
        return (1);
    }

    free(dfile);
    return (-1);
}

/*
 * Unlocks the file by unlinking it from the filesystem
 */
int
__pos4obj_unlock(const char *path, const char *type)
{
    return (__pos4obj_unlink(path, type));
}

/*
 * Removes unused hash and type directories that may exist in specified path.
 */
static void
__pos4obj_clean(char *path)
{
    char    *p;
    int olderrno;

    /*
     * path is either
     * 1) /<objroot>/<type><path>  or
     * 2) /<objroot>/.<hash>/<type>/<path>
     *
     * In case 1, there is nothing to clean.
     *
     * Detect case 2 by looking for a '/' after /objroot/ and
     * remove the two trailing directories, if empty.
     */
    if (strchr(path + strlen(objroot), '/') == NULL)
        return;

    /*
     * Preserve errno across calls to rmdir. See block comment in
     * __pos4obj_name() for explanation.
     */
    olderrno = errno;

    if ((p = strrchr(path, '/')) == NULL)
        return;
    *p = '\0';

    (void) rmdir(path);

    if ((p = strrchr(path, '/')) == NULL)
        return;
    *p = '\0';

    (void) rmdir(path);

    errno = olderrno;
}


/*
 * Check that path starts with a /, does not contain a / within it
 * and is not longer than PATH_MAX or NAME_MAX
 */
int
__pos4obj_check(const char *path)
{
    long int    i;

    /*
     * This assumes that __pos4obj_check() is called before
     * any of the other functions in this file
     */
    if (name_max == 0 || name_max == -1) {
        name_max = pathconf(objroot, _PC_NAME_MAX);
        if (name_max == -1)
            return (-1);
    }

    if (*path++ != '/') {
        errno = EINVAL;
        return (-1);
    }

    for (i = 0; *path != '\0'; i++) {
        if (*path++ == '/') {
            errno = EINVAL;
            return (-1);
        }
    }

    if (i > PATH_MAX || i > name_max) {
        errno = ENAMETOOLONG;
        return (-1);
    }

    return (0);
}