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

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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.
This commit is contained in:
Juan RP 2011-07-06 17:00:59 +02:00
parent 774d662a13
commit 88cd3ff7eb
1 changed files with 53 additions and 4 deletions
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57
xbps-src/libexec/mount.c
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@ -1,8 +1,36 @@
/*-
* 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.
*/
/* /*
* Bind mounts a filesystem mountpoint into the target directory, * Bind mounts a filesystem mountpoint into the target directory,
* by using the CAP_SYS_ADMIN capability set on the file. * by using the CAP_SYS_ADMIN capability set on the program.
* *
* Juan RP - 2010/04/26 - Public Domain. * Only mounts are possible when user running the process owns
* the target directory and has read/write permission on it.
*
* Mounts are also mounted with nosuid for security meassures.
*/ */
#include <stdio.h> #include <stdio.h>
#include <stdlib.h> #include <stdlib.h>
@ -11,12 +39,15 @@
#include <unistd.h> #include <unistd.h>
#include <errno.h> #include <errno.h>
#include <sys/mount.h> #include <sys/mount.h>
#include <sys/stat.h>
#include <sys/capability.h> #include <sys/capability.h>
#define _PROGNAME "xbps-src-chroot-capmount"
void void
usage(void) usage(void)
{ {
fprintf(stderr, "Usage: xbps-src-capbmount [-w] <orig> <dest>\n"); fprintf(stderr, "Usage: %s [-w] <orig> <dest>\n", _PROGNAME);
exit(EXIT_FAILURE); exit(EXIT_FAILURE);
} }
@ -25,6 +56,7 @@ main(int argc, char **argv)
{ {
cap_t cap; cap_t cap;
cap_flag_value_t effective, permitted; cap_flag_value_t effective, permitted;
struct stat st;
unsigned long flags; unsigned long flags;
int c, rv; int c, rv;
bool dowrite = false; bool dowrite = false;
@ -63,10 +95,27 @@ main(int argc, char **argv)
} }
cap_free(cap); cap_free(cap);
flags = MS_BIND; /*
* Bind mount with nosuid.
*/
flags = MS_BIND | MS_NOSUID;
if (!dowrite) if (!dowrite)
flags |= MS_RDONLY; flags |= MS_RDONLY;
/*
* Check that uid/gid owns the dir and has rx perms on it.
*/
if (stat(argv[1], &st) == -1) {
fprintf(stderr, "ERROR: stat() on %s: %s\n",
argv[1], strerror(errno));
exit(EXIT_FAILURE);
}
if ((st.st_uid != getuid()) && (st.st_gid != getgid()) &&
(st.st_mode & (S_IRUSR|S_IXUSR|S_IRGRP|S_IXGRP))) {
fprintf(stderr, "ERROR: wrong permissions on %s!\n", argv[1]);
exit(EXIT_FAILURE);
}
rv = mount(argv[0], argv[1], "none", flags, NULL); rv = mount(argv[0], argv[1], "none", flags, NULL);
if (rv != 0) { if (rv != 0) {
fprintf(stderr, "E: cannot mount %s into %s: %s\n", argv[0], fprintf(stderr, "E: cannot mount %s into %s: %s\n", argv[0],