88cd3ff7eb
The new code now has some security enhancements that only allows to bind mount a filesystem when the user executing the process owns the target directory and has read/write permissions on it.
128 lines
3.5 KiB
C
128 lines
3.5 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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* Bind mounts a filesystem mountpoint into the target directory,
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* by using the CAP_SYS_ADMIN capability set on the program.
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*
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* Only mounts are possible when user running the process owns
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* the target directory and has read/write permission on it.
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*
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* Mounts are also mounted with nosuid for security meassures.
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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/mount.h>
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#include <sys/stat.h>
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#include <sys/capability.h>
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#define _PROGNAME "xbps-src-chroot-capmount"
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void
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usage(void)
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{
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fprintf(stderr, "Usage: %s [-w] <orig> <dest>\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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struct stat st;
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unsigned long flags;
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int c, rv;
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bool dowrite = false;
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while ((c = getopt(argc, argv, "w")) != -1) {
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switch (c) {
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case 'w':
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dowrite = true;
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break;
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default:
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usage();
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}
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}
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argc -= optind;
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argv += optind;
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if (argc != 2)
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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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/*
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* Bind mount with nosuid.
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*/
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flags = MS_BIND | MS_NOSUID;
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if (!dowrite)
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flags |= MS_RDONLY;
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/*
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* Check that uid/gid owns the dir and has rx perms on it.
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*/
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if (stat(argv[1], &st) == -1) {
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fprintf(stderr, "ERROR: stat() on %s: %s\n",
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argv[1], strerror(errno));
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exit(EXIT_FAILURE);
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}
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if ((st.st_uid != getuid()) && (st.st_gid != getgid()) &&
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(st.st_mode & (S_IRUSR|S_IXUSR|S_IRGRP|S_IXGRP))) {
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fprintf(stderr, "ERROR: wrong permissions on %s!\n", argv[1]);
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exit(EXIT_FAILURE);
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}
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rv = mount(argv[0], argv[1], "none", flags, NULL);
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if (rv != 0) {
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fprintf(stderr, "E: cannot mount %s into %s: %s\n", argv[0],
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argv[1], 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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