New security enhancements have been made and now you can only umount a filesystem when the status file ".<mntpnt>_mount_bind_done" is available in the specified masterdir. The arguments have been changed and now it accepts two for <masterdir> and <dir>.
106 lines
3.3 KiB
C
106 lines
3.3 KiB
C
/*-
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* Copyright (c) 2010-2011 Juan Romero Pardines.
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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/*
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* Umounts a mounted filesystem mountpoint as regular user thanks to
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* the CAP_SYS_ADMIN capability flag set on the file. The following
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* arguments are expected: <masterdir> <dir>.
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*
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* As security measure it only accepts to unmount a mount point
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* when the "status" file has been previously written in the masterdir.
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <stdbool.h>
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#include <string.h>
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#include <unistd.h>
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#include <errno.h>
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#include <sys/param.h>
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#include <sys/mount.h>
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#include <sys/capability.h>
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#define _PROGNAME "xbps-src-chroot-capumount"
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void
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usage(void)
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{
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fprintf(stderr, "Usage: %s <masterdir> <dir>\n", _PROGNAME);
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exit(EXIT_FAILURE);
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}
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int
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main(int argc, char **argv)
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{
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cap_t cap;
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cap_flag_value_t effective, permitted;
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char bindf[PATH_MAX - 1];
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int rv;
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if (argc != 3)
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usage();
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cap = cap_get_proc();
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if (cap == NULL) {
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fprintf(stderr, "cap_get_proc() returned %s!\n",
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strerror(errno));
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exit(EXIT_FAILURE);
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}
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cap_get_flag(cap, CAP_SYS_ADMIN, CAP_EFFECTIVE, &effective);
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cap_get_flag(cap, CAP_SYS_ADMIN, CAP_PERMITTED, &permitted);
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if ((effective != CAP_SET) && (permitted != CAP_SET)) {
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fprintf(stderr, "E: missing 'cap_sys_admin' capability!\n"
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"Please set it with: setcap cap_sys_admin=ep %s'\n",
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argv[0]);
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cap_free(cap);
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exit(EXIT_FAILURE);
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}
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cap_free(cap);
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/* Check that status file exists in masterdir */
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rv = snprintf(bindf, sizeof(bindf), "%s/.%s_mount_bind_done",
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argv[1], argv[2]);
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if (rv < 0 || rv >= sizeof(bindf))
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exit(EXIT_FAILURE);
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if (access(bindf, R_OK) == -1) {
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fprintf(stderr, "E: cannot umount %s/%s, missing "
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"status file\n", argv[1], argv[2]);
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exit(EXIT_FAILURE);
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}
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/* Security check passed, continue mounting */
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rv = snprintf(bindf, sizeof(bindf), "%s/%s", argv[1], argv[2]);
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if (rv < 0 || rv >= sizeof(bindf))
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exit(EXIT_FAILURE);
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if ((rv = umount(bindf)) != 0) {
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fprintf(stderr, "E: cannot umount %s: %s\n", argv[1],
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strerror(errno));
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exit(EXIT_FAILURE);
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}
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exit(EXIT_SUCCESS);
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}
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