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xbps-src: improved xbps-src-chroot-capumount helper.

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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>.
This commit is contained in:
Juan RP 2011-07-06 17:02:19 +02:00
parent 88cd3ff7eb
commit b29e482767
2 changed files with 56 additions and 8 deletions
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62
xbps-src/libexec/umount.c
View file

@ -1,8 +1,35 @@
/*
* Umounts a previously bind mounted filesystem mountpoint,
* by using the CAP_SYS_ADMIN capability set on the file.
/*-
* Copyright (c) 2010-2011 Juan Romero Pardines.
* All rights reserved.
*
* Juan RP - 2010/04/26 - Public Domain.
* 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>
@ -10,13 +37,16 @@
#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: xbps-src-capbumount <dest>\n");
fprintf(stderr, "Usage: %s <masterdir> <dir>\n", _PROGNAME);
exit(EXIT_FAILURE);
}
@ -25,9 +55,10 @@ main(int argc, char **argv)
{
cap_t cap;
cap_flag_value_t effective, permitted;
char bindf[PATH_MAX - 1];
int rv;
if (argc != 2)
if (argc != 3)
usage();
cap = cap_get_proc();
@ -48,7 +79,24 @@ main(int argc, char **argv)
}
cap_free(cap);
if ((rv = umount(argv[1])) != 0) {
/* 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);

2
xbps-src/libexec/xbps-src-chroot-helper.sh.in
View file

@ -95,7 +95,7 @@ umount_chroot_fs()
else
echo -n "=> Unmounting ${fs} from chroot... "
@@XBPS_INSTALL_LIBEXECDIR@@/xbps-src-chroot-capumount \
${XBPS_MASTERDIR}/${fs} 2>/dev/null
${XBPS_MASTERDIR} ${fs} 2>/dev/null
if [ $? -eq 0 ]; then
rm -f ${XBPS_MASTERDIR}/.${fs}_mount_bind_done
echo "done."