path: root/src/responder/nss/nsssrv_mmap_cache.c

/*
   SSSD

   NSS Responder - Mmap Cache

   Copyright (C) Simo Sorce <ssorce@redhat.com>	2011

   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 3 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, see <http://www.gnu.org/licenses/>.
*/

#include "util/util.h"
#include "confdb/confdb.h"
#include <sys/mman.h>
#include <fcntl.h>
#include "util/mmap_cache.h"
#include "responder/nss/nsssrv.h"
#include "responder/nss/nsssrv_mmap_cache.h"

/* arbitrary (avg of my /etc/passwd) */
#define SSS_AVG_PASSWD_PAYLOAD (MC_SLOT_SIZE * 4)
/* short group name and no gids (private user group */
#define SSS_AVG_GROUP_PAYLOAD (MC_SLOT_SIZE * 3)

#define MC_NEXT_BARRIER(val) ((((val) + 1) & 0x00ffffff) | 0xf0000000)

#define MC_RAISE_BARRIER(m) do { \
    m->b2 = MC_NEXT_BARRIER(m->b1); \
    __sync_synchronize(); \
} while (0)

#define MC_LOWER_BARRIER(m) do { \
    __sync_synchronize(); \
    m->b1 = m->b2; \
} while (0)

struct sss_mc_ctx {
    char *name;             /* mmap cache name */
    enum sss_mc_type type;  /* mmap cache type */
    char *file;             /* mmap cache file name */
    int fd;                 /* file descriptor */

    uint32_t seed;          /* pseudo-random seed to avoid collision attacks */
    time_t valid_time_slot; /* maximum time the entry is valid in seconds */

    void *mmap_base;        /* base address of mmap */
    size_t mmap_size;       /* total size of mmap */

    uint32_t *hash_table;   /* hash table address (in mmap) */
    uint32_t ht_size;       /* size of hash table */

    uint8_t *free_table;    /* free list bitmaps */
    uint32_t ft_size;       /* size of free table */
    uint32_t next_slot;     /* the next slot after last allocation */

    uint8_t *data_table;    /* data table address (in mmap) */
    uint32_t dt_size;       /* size of data table */
};


/***************************************************************************
 * initialization
 ***************************************************************************/

static errno_t sss_mc_set_recycled(int fd)
{
    uint32_t w = SSS_MC_HEADER_RECYCLED;
    struct sss_mc_header h;
    off_t offset;
    off_t pos;
    int ret;

    offset = MC_PTR_DIFF(&h.status, &h);

    pos = lseek(fd, offset, SEEK_SET);
    if (pos == -1) {
        /* What do we do now ? */
        return errno;
    }
    pos = 0;
    while (pos < sizeof(h.status)) {
        ret = write(fd, ((uint8_t *)&w) + pos, sizeof(h.status) - pos);
        if (ret == -1) {
            if (errno != EINTR) {
                return errno;
            }
            continue;
        }
        pos += ret;
    }

    return EOK;
}

/*
 * When we (re)create a new file we must mark the current file as recycled
 * so active clients will abandon its use asap.
 * We unlink the current file and make a new one
 */
static errno_t sss_mc_create_file(struct sss_mc_ctx *mc_ctx)
{
    mode_t old_mask;
    int ofd;
    int ret;

    ofd = open(mc_ctx->file, O_RDWR);
    if (ofd != -1) {
        ret = sss_mc_set_recycled(ofd);
        if (ret) {
            DEBUG(SSSDBG_TRACE_FUNC, ("Failed to mark mmap file %s as"
                                      " recycled: %d(%s)\n",
                                      mc_ctx->file, ret, strerror(ret)));
        }

        close(ofd);
    }

    ret = unlink(mc_ctx->file);
    if (ret == -1) {
        DEBUG(SSSDBG_TRACE_FUNC, ("Failed to rm mmap file %s: %d(%s)\n",
                                  mc_ctx->file, ret, strerror(ret)));
    }

    /* temporarily relax umask as we need the file to be readable
     * by everyone for now */
    old_mask = umask(0022);

    ret = 0;
    mc_ctx->fd = open(mc_ctx->file, O_CREAT | O_EXCL | O_RDWR, 0644);
    if (mc_ctx->fd == -1) {
        ret = errno;
        DEBUG(SSSDBG_CRIT_FAILURE, ("Failed to open mmap file %s: %d(%s)\n",
                                    mc_ctx->file, ret, strerror(ret)));
    }

    /* reset mask back */
    umask(old_mask);

    return ret;
}

static void sss_mc_header_update(struct sss_mc_ctx *mc_ctx, int status)
{
    struct sss_mc_header *h;

    /* update header using barriers */
    h = (struct sss_mc_header *)mc_ctx->mmap_base;
    MC_RAISE_BARRIER(h);
    if (status != SSS_MC_HEADER_RECYCLED) {
        /* no reason to update anything else if the file is recycled */
        h->hash_table = MC_PTR_DIFF(mc_ctx->hash_table, mc_ctx->mmap_base);
        h->free_table = MC_PTR_DIFF(mc_ctx->free_table, mc_ctx->mmap_base);
        h->data_table = MC_PTR_DIFF(mc_ctx->data_table, mc_ctx->mmap_base);
        h->ht_size = mc_ctx->ht_size;
        h->ft_size = mc_ctx->ft_size;
        h->dt_size = mc_ctx->dt_size;
        h->major_vno = SSS_MC_MAJOR_VNO;
        h->minor_vno = SSS_MC_MINOR_VNO;
        h->seed = mc_ctx->seed;
        h->reserved = 0;
    }
    h->status = status;
    MC_LOWER_BARRIER(h);
}

errno_t sss_mmap_cache_init(TALLOC_CTX *mem_ctx, const char *name,
                            enum sss_mc_type type, size_t n_elem,
                            struct sss_mc_ctx **mcc)
{
    struct sss_mc_ctx *mc_ctx = NULL;
    unsigned int rseed;
    int payload;
    int ret;

    switch (type) {
    case SSS_MC_PASSWD:
        payload = SSS_AVG_PASSWD_PAYLOAD;
        break;
    case SSS_MC_GROUP:
        payload = SSS_AVG_GROUP_PAYLOAD;
        break;
    default:
        return EINVAL;
    }

    mc_ctx = talloc_zero(mem_ctx, struct sss_mc_ctx);
    if (!mc_ctx) {
        return ENOMEM;
    }
    mc_ctx->fd = -1;

    mc_ctx->name = talloc_strdup(mem_ctx, name);
    if (!mc_ctx->name) {
        ret = ENOMEM;
        goto done;
    }

    mc_ctx->type = type;

    mc_ctx->valid_time_slot = 300; /* 5 min. FIXME: parametrize */

    mc_ctx->file = talloc_asprintf(mc_ctx, "%s/%s",
                                   SSS_NSS_MCACHE_DIR, name);
    if (!mc_ctx->file) {
        ret = ENOMEM;
        goto done;
    }

    /* elements must always be multiple of 8 to make things easier to handle,
     * so we increase by the necessary amount if they are not a multiple */
    /* We can use MC_ALIGN64 for this */
    n_elem = MC_ALIGN64(n_elem);

    /* hash table is double the size because it will store both forward and
     * reverse keys (name/uid, name/gid, ..) */
    mc_ctx->ht_size = MC_HT_SIZE(n_elem * 2);
    mc_ctx->dt_size = MC_DT_SIZE(n_elem, payload);
    mc_ctx->ft_size = MC_FT_SIZE(n_elem);
    mc_ctx->mmap_size = MC_HEADER_SIZE +
                        MC_ALIGN64(mc_ctx->dt_size) +
                        MC_ALIGN64(mc_ctx->ft_size) +
                        MC_ALIGN64(mc_ctx->ht_size);


    /* for now ALWAYS create a new file on restart */

    ret = sss_mc_create_file(mc_ctx);
    if (ret) {
        goto done;
    }

    ret = ftruncate(mc_ctx->fd, mc_ctx->mmap_size);
    if (ret == -1) {
        ret = errno;
        DEBUG(SSSDBG_CRIT_FAILURE, ("Failed to resize file %s: %d(%s)\n",
                                    mc_ctx->file, ret, strerror(ret)));
        goto done;
    }

    mc_ctx->mmap_base = mmap(NULL, mc_ctx->mmap_size,
                             PROT_READ | PROT_WRITE,
                             MAP_SHARED, mc_ctx->fd, 0);
    if (mc_ctx->mmap_base == MAP_FAILED) {
        ret = errno;
        DEBUG(SSSDBG_CRIT_FAILURE, ("Failed to mmap file %s(%ld): %d(%s)\n",
                                    mc_ctx->file, mc_ctx->mmap_size,
                                    ret, strerror(ret)));
        goto done;
    }

    mc_ctx->data_table = MC_PTR_ADD(mc_ctx->mmap_base, MC_HEADER_SIZE);
    mc_ctx->free_table = MC_PTR_ADD(mc_ctx->data_table,
                                    MC_ALIGN64(mc_ctx->dt_size));
    mc_ctx->hash_table = MC_PTR_ADD(mc_ctx->free_table,
                                    MC_ALIGN64(mc_ctx->ft_size));

    memset(mc_ctx->data_table, 0x00, mc_ctx->dt_size);
    memset(mc_ctx->free_table, 0x00, mc_ctx->ft_size);
    memset(mc_ctx->hash_table, 0xff, mc_ctx->ht_size);

    /* generate a pseudo-random seed.
     * Needed to fend off dictionary based collision attacks */
    rseed = time(NULL) * getpid();
    mc_ctx->seed = rand_r(&rseed);

    sss_mc_header_update(mc_ctx, SSS_MC_HEADER_ALIVE);

    ret = EOK;

done:
    if (ret) {
        if (mc_ctx && mc_ctx->mmap_base) {
            munmap(mc_ctx->mmap_base, mc_ctx->mmap_size);
        }
        if (mc_ctx && mc_ctx->fd != -1) {
            close(mc_ctx->fd);
            ret = unlink(mc_ctx->file);
            if (ret == -1) {
                DEBUG(SSSDBG_CRIT_FAILURE, ("Failed to rm mmap file %s: %d(%s)\n",
                                            mc_ctx->file, ret, strerror(ret)));
            }
        }

        talloc_free(mc_ctx);
    } else {
        *mcc = mc_ctx;
    }
    return ret;
}