void-packages/xbps-src/libexec/umount.c

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