143 lines
4.5 KiB
C++
143 lines
4.5 KiB
C++
/* -*- Mode: C; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4; fill-column: 100 -*- */
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/*
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/.
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*/
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/*
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* This is a very tiny helper to allow overlay mounting.
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*/
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#include <config.h>
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#include <stdio.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 <unistd.h>
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#include <security.h>
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void usage(const char* program)
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{
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fprintf(stderr, "Usage: %s <-s|-r> <source path> <target path>\n", program);
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fprintf(stderr, " %s -u <target>.\n", program);
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fprintf(stderr, " -b bind and mount the source to target.\n");
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fprintf(stderr, " -r bind and mount the source to target as readonly.\n");
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fprintf(stderr, " -u to unmount the target.\n");
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}
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int main(int argc, char** argv)
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{
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const char* program = argv[0];
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if (!hasCorrectUID("loolmount"))
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{
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fprintf(stderr, "%s: incorrect UID.", program);
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return 1;
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}
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if (argc < 3)
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{
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usage(program);
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return 1;
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}
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const char* option = argv[1];
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if (argc == 3 && strcmp(option, "-u") == 0) // Unmount
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{
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const char* target = argv[2];
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struct stat sb;
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const bool target_exists = (stat(target, &sb) == 0 && S_ISDIR(sb.st_mode));
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// Do nothing if target doesn't exist.
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if (target_exists)
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{
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// Unmount the target, first by detaching. This should succeed.
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int retval = umount2(target, MNT_DETACH);
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if (retval != 0)
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{
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if (errno != EINVAL)
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fprintf(stderr, "%s: unmount failed to detach [%s]: %s.\n", program, target,
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strerror(errno));
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}
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// Now try to force the unmounting, which isn't supported on all filesystems.
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retval = umount2(target, MNT_FORCE);
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if (retval && errno != EINVAL)
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{
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fprintf(stderr, "%s: forced unmount of [%s] failed: %s.\n", program, target,
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strerror(errno));
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return 1;
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}
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}
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}
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else if (argc == 4) // Mount
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{
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const char* source = argv[2];
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struct stat sb;
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if (stat(source, &sb) != 0 || !S_ISDIR(sb.st_mode))
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{
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fprintf(stderr, "%s: cannot mount from invalid source directory [%s].\n", program,
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source);
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return 1;
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}
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const char* target = argv[3];
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const bool target_exists = (stat(target, &sb) == 0 && S_ISDIR(sb.st_mode));
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if (!target_exists)
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{
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fprintf(stderr, "%s: cannot mount on invalid target directory [%s].\n", program,
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target);
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return 1;
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}
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// Mount the source path as the target path.
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// First bind to mount an existing directory node into the chroot.
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// MS_BIND ignores other flags.
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if (strcmp(option, "-b") == 0) // Shared or Bind Mount.
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{
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const int retval
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= mount(source, target, nullptr, (MS_MGC_VAL | MS_BIND | MS_REC), nullptr);
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if (retval)
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{
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fprintf(stderr, "%s: mount failed to bind [%s] to [%s]: %s.\n", program, source,
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target, strerror(errno));
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return 1;
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}
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}
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else if (strcmp(option, "-r") == 0) // Readonly Mount.
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{
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// Now we need to set read-only and other flags with a remount.
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int retval = mount(source, target, nullptr,
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(MS_BIND | MS_REC | MS_REMOUNT | MS_NOATIME | MS_NODEV | MS_NOSUID
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| MS_RDONLY | MS_SILENT),
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nullptr);
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if (retval)
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{
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fprintf(stderr, "%s: mount failed remount [%s] readonly: %s.\n", program, target,
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strerror(errno));
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return 1;
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}
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retval = mount(source, target, nullptr, (MS_UNBINDABLE | MS_REC), nullptr);
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if (retval)
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{
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fprintf(stderr, "%s: mount failed make [%s] private: %s.\n", program, target,
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strerror(errno));
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return 1;
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}
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}
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}
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else
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{
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usage(program);
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return 1;
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}
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fflush(stderr);
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return 0;
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}
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/* vim:set shiftwidth=4 softtabstop=4 expandtab: */
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