fsutils.c

/*
 *  Filesystem-related utilities for cryptmount
 *  (C)Copyright 2005-2023, RW Penney
 */

/*
    This file is part of cryptmount

    cryptmount 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.

    cryptmount 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.,
    51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

#include "config.h"

#include <ctype.h>
#include <fcntl.h>
#include <math.h>
#include <mntent.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <sys/statvfs.h>
#if HAVE_SYS_SYSMACROS_H
#  include <sys/sysmacros.h>
#endif
#include <sys/types.h>
#include <sys/wait.h>

#include "cryptmount.h"
#include "delegates.h"
#include "dmutils.h"
#include "fsutils.h"
#if WITH_CSWAP
#  include <sys/swap.h>
#endif
#ifdef TESTING
#  include "cmtesting.h"
#endif


static const char *ETCMTAB = "/etc/mtab",
                  *ETCMTABTMP = "/etc/mtab.cm",
                  *STDPATH = CM_DEFAULT_SUPATH;


enum {
    F_MATCHUID =  0x01,     /*!< Set real UID to match effective UID */
    F_CLOSE1 =    0x02,     /*!< Close stdout on child process */
    F_SETPATH =   0x04      /*!< Set standard PATH for child process */
};
static int run_sucommand(const char *path, const char *argv[],
                        const char *supath, unsigned switches);
int do_addmntent(const tgtdefn_t *tgt);
int do_rmvmntent(const tgtdefn_t *tgt);


static char **split_fsckopts(const char *fsckoptions, unsigned *argc)
    /*! Split options separated by ';' into vector of strings */
{   const char SEP = ';';
    const char *pos, *posnext;
    size_t optlen;
    char **opttable=NULL;
    size_t tablesize = 0;

    *argc = 0;
    if (fsckoptions == NULL || *fsckoptions == '\0') return opttable;

    pos = fsckoptions;
    do {
        if (*argc >= tablesize) {
            tablesize = (tablesize + 8) * 2;
            opttable = (char**)realloc((void*)opttable,
                                        (size_t)(tablesize * sizeof(char*)));
        }

        posnext = pos;
        optlen = 0;
        while (*posnext != SEP && *posnext != '\0') {
            ++posnext;
            ++optlen;
        }

        opttable[*argc] = (char*)malloc(optlen + 1);
        strncpy(opttable[*argc], pos, optlen);
        opttable[*argc][optlen] = '\0';

        ++*argc;
        pos = posnext + 1;
    } while (*posnext != '\0');

    return opttable;
}


#if ERSATZ_MOUNT

static int parse_mountoptions(const char *buff, unsigned long *mflags)
    /*! Convert string of mount-options into binary flags */
{   struct fsopt_t {
        const char *str;
        unsigned long mask; };
    struct fsopt_t fsopts[] = {
        { "defaults",   0 },
        { "noatime",    MS_NOATIME },
        { "nodev",      MS_NODEV },
        { "noexec",     MS_NOEXEC },
        { "nosuid",     MS_NOSUID },
        { "ro",         MS_RDONLY },
        { "sync",       MS_SYNCHRONOUS },
        { NULL, 0 } };
    unsigned idx,len;

    *mflags = 0;
    if (buff == NULL) return 0;

    for (;;) {
        for (len=0; buff[len]!='\0' && buff[len]!=','; ++len);
        for (idx=0; fsopts[idx].str!=NULL; ++idx) {
            if (strncmp(buff, fsopts[idx].str, (size_t)len) == 0) {
                *mflags |= fsopts[idx].mask;
                break;
            }
        }
        if (fsopts[idx].str == NULL) {
            fprintf(stderr, "bad option \"%s\"\n", buff);
            return 1;
        }

        if (buff[len] == '\0') break;
        buff += len + 1;
    }

    return 0;
}


int fs_mount(const char *mntdev, const tgtdefn_t *tgt)
    /*! Fallback version of mount(8) using mount(2) */
{   unsigned long mflags;
    int eflag=ERR_NOERROR;
    char *errstr=NULL;

    if (parse_mountoptions(tgt->mountoptions, &mflags) != 0) {
        return ERR_BADMOUNT;
    }

    errstr = (char*)malloc((size_t)(strlen(mntdev) + strlen(tgt->dir) + 64));
    sprintf(errstr, "mounting \"%s\" on \"%s\" failed", mntdev, tgt->dir);

    if (mount(mntdev, tgt->dir, tgt->fstype, mflags, NULL) == 0) {
        (void)do_addmntent(tgt);
    } else {
        perror(errstr);
        eflag = ERR_BADMOUNT;
    }

    free((void*)errstr);

    return eflag;
}

#else   /* !ERSATZ_MOUNT */

int fs_mount(const char *dev, const tgtdefn_t *tgt)
    /*! Delegate filesystem mounting to mount(8) */
{   int idx, stat, eflag=ERR_NOERROR;
    const char *argv[16];

    /* Construct argument list for mount -t ... -o ... <dev> <dir> */
    idx = 0;
    argv[idx++] = "[cryptmount-mount]";
    if (tgt->fstype != NULL) {
        argv[idx++] = "-t"; argv[idx++] = tgt->fstype;
    }
    if (tgt->mountoptions != NULL) {
        argv[idx++] = "-o"; argv[idx++] = tgt->mountoptions;
    }
    argv[idx++] = dev; argv[idx++] = tgt->dir;
    argv[idx++] = NULL;

    stat = run_sucommand(DLGT_MOUNT, argv, tgt->supath, F_MATCHUID);
    eflag = (stat != 0 ? ERR_BADMOUNT: ERR_NOERROR);

    return eflag;
}

#endif  /* ERSATZ_MOUNT */


#if ERSATZ_UMOUNT

int fs_unmount(const tgtdefn_t *tgt)
    /*! Fallback version of umount(8) using umount(2) */
{   int eflag=ERR_NOERROR;
    char *errstr=NULL;

    errstr = (char*)malloc((size_t)(strlen(tgt->dir) + 64));
    sprintf(errstr, "unmounting \"%s\" failed", tgt->dir);

    if (umount(tgt->dir) == 0) {
        (void)do_rmvmntent(tgt);
    } else {
        perror(errstr);
        eflag = ERR_BADMOUNT;
    }

    free((void*)errstr);

    return eflag;
}

#else   /* !ERSATZ_UMOUNT */

int fs_unmount(const tgtdefn_t *tgt)
    /*! Delegate filesystem mounting to umount(8) */
{   int idx, stat, eflag=ERR_NOERROR;
    const char *argv[16];

    /* Construct argument list for umount -t ... <dir> */
    idx = 0;
    argv[idx++] = "[cryptmount-umount]";
#ifdef PARANOID
    if (tgt->fstype != NULL) {
        argv[idx++] = "-t"; argv[idx++] = tgt->fstype;
    }
    if (tgt->mountoptions != NULL) {
        argv[idx++] = "-O"; argv[idx++] = tgt->mountoptions;
    }
#endif
    argv[idx++] = tgt->dir;
    argv[idx++] = NULL;

    stat = run_sucommand(DLGT_UMOUNT, argv, tgt->supath, F_MATCHUID);
    eflag = (stat != 0 ? ERR_BADMOUNT: ERR_NOERROR);

    return eflag;
}

#endif  /* ERSATZ_UMOUNT */


#if WITH_CSWAP

int fs_swapon(const char *mntdev, const tgtdefn_t *tgt)
    /*! Install \a mntdev as a new swap device */
{   int idx, stat, prio, rawprio = 0x100, expendable = 0, eflag=ERR_NOERROR;
    const char *argv[8];
    double cry_entropy = 0.0, raw_entropy = 0.0;
    const size_t entrosize = 1 << 20;
    const double blank_thresh = 1e-5, noise_thresh = 7.0;

    if (strcmp(tgt->fstype,"swap") != 0) {
        fprintf(stderr, _("Unsuitable filesystem type \"%s\" for swapping\n"),
                tgt->fstype);
        eflag = ERR_BADSWAP;
        goto bail_out;
    }

    /*  Measure entropy of filesystem and underlying raw device
        to check whether it's safe to force mkswap to format
        what it thinks is a whole disk(!), or which could be
        a file containing wanted data: */
    raw_entropy = fs_entropy(tgt->dev, entrosize);
    cry_entropy = fs_entropy(mntdev, entrosize);
    expendable = (raw_entropy < blank_thresh)
                || (cry_entropy < blank_thresh)
                || (raw_entropy > noise_thresh && cry_entropy > noise_thresh);

    if ((tgt->flags & FLG_MKSWAP) != 0) {
        if (expendable) {
            /* Construct argument list for mkswap <dev> */
            idx = 0;
            argv[idx++] = "[cryptmount-mkswap]";
            if (expendable) argv[idx++] = "-f";
            argv[idx++] = mntdev;
            argv[idx++] = NULL;

            stat = run_sucommand(DLGT_MKSWAP, argv,
                                 tgt->supath, F_CLOSE1);
            eflag = (stat != 0 ? ERR_BADSWAP : ERR_NOERROR);
            if (eflag != ERR_NOERROR) goto bail_out;
        } else {
            fprintf(stderr, _("Device \"%s\" appears to contain data (entropy=%.3g,%.3g) - please run mkswap manually\n"), tgt->dev, raw_entropy, cry_entropy);
        }
    }

    if (tgt->mountoptions != NULL
      && sscanf(tgt->mountoptions, "pri=%i", &prio) == 1) {
        rawprio = prio;
    }

    prio = ( SWAP_FLAG_PREFER |
            ((rawprio << SWAP_FLAG_PRIO_SHIFT) & SWAP_FLAG_PRIO_MASK) );
    if (swapon(mntdev, prio) != 0) {
        eflag = ERR_BADSWAP;
        goto bail_out;
    }

  bail_out:

    return eflag;
}


int fs_swapoff(const tgtdefn_t *tgt)
{   char *mntdev=NULL;
    int eflag=ERR_NOERROR;

    if (strcmp(tgt->fstype,"swap") != 0) {
        eflag = ERR_BADSWAP;
        goto bail_out;
    }

    devmap_path(&mntdev, tgt->ident);

    if (swapoff(mntdev) != 0) {
        eflag = ERR_BADSWAP;
        goto bail_out;
    }

  bail_out:

    if (mntdev != NULL) free((void*)mntdev);

    return eflag;
}

#endif  /* WITH_CSWAP */


int do_addmntent(const tgtdefn_t *tgt)
    /*! Add entry into /etc/mtab for newly-mounted filing system */
{   char *mntdev = NULL;
    struct mntent mntinfo;
    FILE *fp;
    int eflag=ERR_NOERROR;

    devmap_path(&mntdev, tgt->ident);

    mntinfo.mnt_fsname = mntdev;
    mntinfo.mnt_dir = tgt->dir;
    mntinfo.mnt_type = tgt->fstype;
    mntinfo.mnt_opts = "none";
    mntinfo.mnt_freq = 0;
    mntinfo.mnt_passno = 0;

    fp = setmntent(ETCMTAB, "a");
    if (fp == NULL) {
        eflag = ERR_BADFILE;
        goto bail_out;
    }
    (void)addmntent(fp, &mntinfo);
    endmntent(fp);

  bail_out:

    if (mntdev != NULL) free((void*)mntdev);

    return eflag;
}


int do_rmvmntent(const tgtdefn_t *tgt)
    /*! Remove entry from /etc/mtab after unmounting filing system */
{   char *mntdev=NULL;
    struct mntent *mntinfo;
    FILE *fp_in=NULL,*fp_out=NULL;
    struct stat sbuff;
    int i,eflag=ERR_NOERROR,found=0;

    /* FIXME - add lots more checks on integrity: */

    devmap_path(&mntdev, tgt->ident);

    /* Open old /etc/mtab & create temporary replacement: */
    fp_in = setmntent(ETCMTAB, "r");
    fp_out = setmntent(ETCMTABTMP, "w");
    if (fp_in == NULL || fp_out == NULL) {
        eflag = ERR_BADFILE;
        goto bail_out;
    }

    i = stat(ETCMTAB, &sbuff);
    if (i != 0 || !S_ISREG(sbuff.st_mode)) {
        fprintf(stderr, "%s is not a valid file\n", ETCMTAB);
        eflag = ERR_BADFILE;
        goto bail_out;
    }

    /* Transfer entries from old /etc/mtab to prototype replacement file: */
    while ((mntinfo = getmntent(fp_in)) != NULL) {
        if (strcmp(mntinfo->mnt_fsname, mntdev) == 0
          && strcmp(mntinfo->mnt_dir, tgt->dir) == 0) {
            ++found;
        } else {
            addmntent(fp_out, mntinfo);
        }
    }

    /* Transfer ownership & permissions from old /etc/mtab to new: */
    if (chown(ETCMTABTMP, sbuff.st_uid, sbuff.st_gid) != 0
      || chmod(ETCMTABTMP, sbuff.st_mode) != 0) {
        fprintf(stderr, "cannot transfer ownership/modes to \"%s\"\n",
                ETCMTABTMP);
        eflag = ERR_BADFILE;
        goto bail_out;
    }

    endmntent(fp_in); fp_in = NULL;

    if (rename(ETCMTABTMP, ETCMTAB)) {
        fprintf(stderr, "Failed to recreate %s\n", ETCMTAB);
    }

  bail_out:

    if (fp_in != NULL) endmntent(fp_in);
    if (fp_out != NULL) endmntent(fp_out);
    if (mntdev != NULL) free((void*)mntdev);

    return eflag;
}


/*!
 *  Check whether a filesystem target is mounted.
 *
 *  This will examine entries in /etc/mtab via getmntent(),
 *  looking for a filesystem whose major and minor device numbers
 *  match those of the block device associated with the supplied target.
 *
 *  Note that this will return false for targets that refer
 *  to swap partitions, even if they are active.
 */
int is_mounted(const tgtdefn_t *tgt)
{   int mounted = 0;
    char *mntdev = NULL;
    struct mntent *mntinfo;
    struct stat st_mtb, st_tgt;
    FILE *fp;

    /* check if underlying device has been configured at all: */
    if (!is_configured(tgt->ident, NULL)) return 0;

    /* find path to device that would have been mounted & device info: */
    devmap_path(&mntdev, tgt->ident);
    if (stat(mntdev, &st_tgt) != 0) {
      mounted = 0;
      goto bail_out;
    }

    /* check entries in /etc/mtab: */
    fp = setmntent(ETCMTAB, "r");
    if (fp == NULL) {
        /* indeterminate case - assume not mounted */
        mounted = 0;
        goto bail_out;
    }
    while ((mntinfo = getmntent(fp)) != NULL && !mounted) {
        if (stat(mntinfo->mnt_fsname, &st_mtb) != 0) continue;

        /* compare to mounted device on basis of kernel device maj/min: */
        if (major(st_mtb.st_rdev) == major(st_tgt.st_rdev)
          && minor(st_mtb.st_rdev) == minor(st_tgt.st_rdev)) {
            mounted = 1;
        }
    }
    endmntent(fp);

  bail_out:
    if (mntdev) free((void*)mntdev);

    return mounted;
}


int is_readonlyfs(const char *path)
    /*! Check if filesystem containing *path is read-only */
{   struct statvfs sbuff;

    return (path == NULL
            || (statvfs(path, &sbuff) != 0
            || (sbuff.f_flag & ST_RDONLY) != 0));
}


#if WITH_FSCK

int fs_check(const char *dev, const tgtdefn_t *tgt)
    /*! Run 'fsck' on target filesystem */
{   int idx, stat, eflag=ERR_NOERROR;
    unsigned pos, n_opts = 0;
    const char **opts = NULL, **argv = NULL;

    if (tgt->fsckoptions != NULL) {
        opts = (const char**)split_fsckopts(tgt->fsckoptions, &n_opts);
    }
    argv = (const char**)malloc((16 + n_opts) * sizeof(char*));

    /* Construct argument list for fsck -T -t ... <dev> */
    idx = 0;
    argv[idx++] = "[cryptmount-fsck]";
    argv[idx++] = "-T";
    if (tgt->fstype != NULL) {
        argv[idx++] = "-t"; argv[idx++] = tgt->fstype;
    }
    for (pos=0; pos<n_opts; ++pos) argv[idx++] = opts[pos];
    argv[idx++] = dev;
    argv[idx++] = NULL;

    stat = run_sucommand(DLGT_FSCK, argv,
                         tgt->supath, F_MATCHUID | F_SETPATH);
    eflag = ((stat == 0 || stat == 1) ? ERR_NOERROR : ERR_BADFSCK);

    if (opts != NULL) {
        for (pos=0; pos<n_opts; ++pos) free((void*)opts[pos]);
        free((void*)opts);
    }
    free((void*)argv);

    return eflag;
}

#endif  /* WITH_FSCK */


double fs_entropy(const char *dev, const size_t blklen)
    /*! Calculate degree of randomness on initial block of filesystem */
{   unsigned *counts = NULL;
    uint8_t buff[4096];
    size_t chunk, totcount = 0;
    int fd, step, i;
    double plogp = 0.0;

    fd = open(dev, O_RDONLY | O_NOATIME);
    if (fd < 0) return -1.0;

    counts = (unsigned*)calloc((size_t)256, sizeof(counts[0]));

    while (totcount < blklen) {
        chunk = blklen - totcount;
        if (chunk > sizeof(buff)) chunk = sizeof(buff);

        step = read(fd, (void*)buff, chunk);
        if (step <= 0) break;

        for (i=0; i<step; ++i) ++counts[buff[i]];

        totcount += step;
    }

    if (totcount > 0) {
        for (i=0; i<256; ++i) {
            if (counts[i] == 0) continue;
            plogp -= counts[i] * log((double)counts[i]);
        }
        plogp = (plogp / totcount) + log((double)totcount);
    }

    plogp /= log(2.0);

    free((void*)counts);
    close(fd);

    return plogp;
}


#if !ERSATZ_MOUNT || !ERSATZ_UMOUNT || WITH_FSCK || WITH_CSWAP

static int run_sucommand(const char *path, const char **argv,
                         const char *supath, unsigned switches)
    /*! Fork (& wait for) system-command as root */
{   pid_t child;
    int stat=-1, fd;

    switch ((child = fork())) {
        case -1:        /* fork failed */
            fprintf(stderr, "failed to fork (%s)\n", path);
            break;
        case 0:         /* child fork */
            if ((switches & F_MATCHUID) != 0) {
                /* change real UID to match effective UID
                   (probably only useful if euid==root): */
                if (setuid(geteuid()) != 0) exit(EXIT_BADEXEC);
            }
            if ((switches & F_CLOSE1) != 0) {
                /* redirect standard output to /dev/null */
                fd = open("/dev/null", O_WRONLY);
                if (fd >= 0) (void)dup2(fd, STDOUT_FILENO);
                else (void)close(STDOUT_FILENO);
            }
            if ((switches & F_SETPATH) != 0) {
                if (supath == NULL) supath = STDPATH;
                if (setenv("PATH", supath, 1) != 0) {
                  exit(EXIT_BADEXEC);
                }
            }

            execv(path, (char *const *)argv);
            fprintf(stderr, "failed to invoke \"%s\"\n", path);
            exit(EXIT_BADEXEC);
            break;
        default:        /* parent fork */
            if (waitpid(child, &fd, 0) == child) {
                stat = fd;
            }
            break;
    }

    return stat;
}

#endif  /* !ERSATZ_MOUNT ... */


#ifdef TESTING

/*! \addtogroup unit_tests
 *  @{ */

int fs_test_splitopts()
{   char **opttable, buff[256];
    unsigned argc, idx, limit;
    const char *SEP = ";", *optsrc[] = { "The", "rain", "in", "Spain", "falls", "mainly", "in", "the", "plain", ",allegedly", NULL };

    CM_TEST_START("Splitting fsck options");

    argc = 17;
    opttable = split_fsckopts(NULL, &argc);
    CM_ASSERT_EQUAL(0, argc);
    CM_ASSERT_EQUAL(NULL, opttable);

    argc = 34;
    opttable = split_fsckopts("", &argc);
    CM_ASSERT_EQUAL(0, argc);
    CM_ASSERT_EQUAL(NULL, opttable);

    for (limit=0; optsrc[limit] != NULL; ++limit) {
        buff[0] = '\0';
        for (idx=0; idx<=limit; ++idx) {
            strcat(buff, optsrc[idx]);
            if (idx < limit) strcat(buff, SEP);
        }

        opttable = split_fsckopts(buff, &argc);
        CM_ASSERT_EQUAL((limit+1), argc);

        for (idx=0; idx<argc; ++idx) {
            CM_ASSERT_DIFFERENT(optsrc[idx], opttable[idx]);

            if (strcmp(optsrc[idx], opttable[idx]) != 0) {
                CM_TEST_FAIL("String mismatch");
            }
        }

        for (idx=0; idx<argc; ++idx) free((void*)opttable[idx]);
        free((void*)opttable);
    }

    CM_TEST_OK();
}


/*!
 *  Check calculation of entropy of files containing
 *  uniformly distributed sequences of bytes.
 */
int fs_test_entropy()
{   char fname[256];
    unsigned i, nbits, mask, offset;
    size_t count;
    FILE *fp;
    double S;
    int its = 1000;

    CM_TEST_START("Entropy calculation");

    sprintf(fname, "/tmp/cm-%u-entropy", (unsigned)getpid());

    while (its--) {
        nbits = (rand() & 7) + 1;
        mask = (1 << nbits) - 1;

        count = (1 << nbits) * ((rand() & 31) + 1);
        offset = (rand() & 0xff);

        fp = fopen(fname, "wb");
        for (i=0; i<count; ++i) {
            fputc((i + offset) & mask, fp);
        }
        fclose(fp);

        S = fs_entropy(fname, count);
        if (fabs(nbits - S) > 1e-2) CM_TEST_FAIL("Mismatch");
    }

    (void)unlink(fname);

    CM_TEST_OK();
}

/** @} */

#endif  /* TESTING */

/*
 *  (C)Copyright 2005-2023, RW Penney
 */