5.1.0/src/path/binding.c

/* -*- c-set-style: "K&R"; c-basic-offset: 8 -*-
 *
 * This file is part of PRoot.
 *
 * Copyright (C) 2014 STMicroelectronics
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301 USA.
 */

#include <sys/stat.h> /* lstat(2), */
#include <unistd.h>   /* getcwd(2), lstat(2), */
#include <string.h>   /* string(3),  */
#include <strings.h>  /* bzero(3), */
#include <assert.h>   /* assert(3), */
#include <limits.h>   /* PATH_MAX, */
#include <errno.h>    /* E* */
#include <sys/queue.h> /* CIRCLEQ_*, */
#include <talloc.h>   /* talloc_*, */

#include "path/binding.h"
#include "path/path.h"
#include "path/canon.h"
#include "cli/note.h"

#include "compat.h"

#define HEAD(tracee, side)						\
	(side == GUEST							\
		? (tracee)->fs->bindings.guest				\
		: (side == HOST						\
			? (tracee)->fs->bindings.host			\
			: (tracee)->fs->bindings.pending))

#define NEXT(binding, side)						\
	(side == GUEST							\
		? CIRCLEQ_NEXT(binding, link.guest)			\
		: (side == HOST						\
			? CIRCLEQ_NEXT(binding, link.host)		\
			: CIRCLEQ_NEXT(binding, link.pending)))

#define CIRCLEQ_FOREACH_(tracee, binding, side)				\
	for (binding = CIRCLEQ_FIRST(HEAD(tracee, side));		\
	     binding != (void *) HEAD(tracee, side);			\
	     binding = NEXT(binding, side))

#define CIRCLEQ_INSERT_AFTER_(tracee, previous, binding, side) do {	\
	switch (side) {							\
	case GUEST: CIRCLEQ_INSERT_AFTER(HEAD(tracee, side), previous, binding, link.guest);   break; \
	case HOST:  CIRCLEQ_INSERT_AFTER(HEAD(tracee, side), previous, binding, link.host);    break; \
	default:    CIRCLEQ_INSERT_AFTER(HEAD(tracee, side), previous, binding, link.pending); break; \
	}								\
	(void) talloc_reference(HEAD(tracee, side), binding);		\
} while (0)

#define CIRCLEQ_INSERT_BEFORE_(tracee, next, binding, side) do {	\
	switch (side) {							\
	case GUEST: CIRCLEQ_INSERT_BEFORE(HEAD(tracee, side), next, binding, link.guest);   break; \
	case HOST:  CIRCLEQ_INSERT_BEFORE(HEAD(tracee, side), next, binding, link.host);    break; \
	default:    CIRCLEQ_INSERT_BEFORE(HEAD(tracee, side), next, binding, link.pending); break; \
	}								\
	(void) talloc_reference(HEAD(tracee, side), binding);		\
} while (0)

#define CIRCLEQ_INSERT_HEAD_(tracee, binding, side) do {		\
	switch (side) {							\
	case GUEST: CIRCLEQ_INSERT_HEAD(HEAD(tracee, side), binding, link.guest);   break; \
	case HOST:  CIRCLEQ_INSERT_HEAD(HEAD(tracee, side), binding, link.host);    break; \
	default:    CIRCLEQ_INSERT_HEAD(HEAD(tracee, side), binding, link.pending); break; \
	}								\
	(void) talloc_reference(HEAD(tracee, side), binding);		\
} while (0)

#define IS_LINKED(binding, link)					\
	((binding)->link.cqe_next != NULL && (binding)->link.cqe_prev != NULL)

#define CIRCLEQ_REMOVE_(tracee, binding, name) do {			\
	CIRCLEQ_REMOVE((tracee)->fs->bindings.name, binding, link.name);\
	(binding)->link.name.cqe_next = NULL;				\
	(binding)->link.name.cqe_prev = NULL;				\
	talloc_unlink((tracee)->fs->bindings.name, binding);		\
} while (0)


/**
 * Print all bindings (verbose purpose).
 */
static void print_bindings(const Tracee *tracee)
{
	const Binding *binding;

	if (tracee->fs->bindings.guest == NULL)
		return;

	CIRCLEQ_FOREACH_(tracee, binding, GUEST) {
		if (compare_paths(binding->host.path, binding->guest.path) == PATHS_ARE_EQUAL)
			note(tracee, INFO, USER, "binding = %s", binding->host.path);
		else
			note(tracee, INFO, USER, "binding = %s:%s",
				binding->host.path, binding->guest.path);
	}
}

/**
 * Get the binding for the given @path (relatively to the given
 * binding @side).
 */
Binding *get_binding(const Tracee *tracee, Side side, const char path[PATH_MAX])
{
	Binding *binding;
	size_t path_length = strlen(path);

	/* Sanity checks.  */
	assert(path != NULL && path[0] == '/');

	CIRCLEQ_FOREACH_(tracee, binding, side) {
		Comparison comparison;
		const Path *ref;

		switch (side) {
		case GUEST:
			ref = &binding->guest;
			break;

		case HOST:
			ref = &binding->host;
			break;

		default:
			assert(0);
			return NULL;
		}

		comparison = compare_paths2(ref->path, ref->length, path, path_length);
		if (   comparison != PATHS_ARE_EQUAL
		    && comparison != PATH1_IS_PREFIX)
			continue;

		/* Avoid false positive when a prefix of the rootfs is
		 * used as an asymmetric binding, ex.:
		 *
		 *     proot -m /usr:/location /usr/local/slackware
		 */
		if (   side == HOST
		    && compare_paths(get_root(tracee), "/") != PATHS_ARE_EQUAL
		    && belongs_to_guestfs(tracee, path))
				continue;

		return binding;
	}

	return NULL;
}

/**
 * Get the binding path for the given @path (relatively to the given
 * binding @side).
 */
const char *get_path_binding(const Tracee *tracee, Side side, const char path[PATH_MAX])
{
	const Binding *binding;

	binding = get_binding(tracee, side, path);
	if (!binding)
		return NULL;

	switch (side) {
	case GUEST:
		return binding->guest.path;

	case HOST:
		return binding->host.path;

	default:
		assert(0);
		return NULL;
	}
}

/**
 * Return the path to the guest rootfs for the given @tracee, from the
 * host point-of-view obviously.  Depending on whether
 * initialize_bindings() was called or not, the path is retrieved from
 * the "bindings.guest" list or from the "bindings.pending" list,
 * respectively.
 */
const char *get_root(const Tracee* tracee)
{
	const Binding *binding;

	if (tracee == NULL || tracee->fs == NULL)
		return NULL;

	if (tracee->fs->bindings.guest == NULL) {
		if (tracee->fs->bindings.pending == NULL
		    || CIRCLEQ_EMPTY(tracee->fs->bindings.pending))
			return NULL;

		binding = CIRCLEQ_LAST(tracee->fs->bindings.pending);
		if (compare_paths(binding->guest.path, "/") != PATHS_ARE_EQUAL)
			return NULL;

		return binding->host.path;
	}

	assert(!CIRCLEQ_EMPTY(tracee->fs->bindings.guest));

	binding = CIRCLEQ_LAST(tracee->fs->bindings.guest);

	assert(strcmp(binding->guest.path, "/") == 0);

	return binding->host.path;
}

/**
 * Substitute the guest path (if any) with the host path in @path.
 * This function returns:
 *
 *     * -errno if an error occured
 *
 *     * 0 if it is a binding location but no substitution is needed
 *       ("symetric" binding)
 *
 *     * 1 if it is a binding location and a substitution was performed
 *       ("asymmetric" binding)
 */
int substitute_binding(const Tracee *tracee, Side side, char path[PATH_MAX])
{
	const Path *reverse_ref;
	const Path *ref;
	const Binding *binding;

	binding = get_binding(tracee, side, path);
	if (!binding)
		return -ENOENT;

	/* Is it a "symetric" binding?  */
	if (!binding->need_substitution)
		return 0;

	switch (side) {
	case GUEST:
		ref = &binding->guest;
		reverse_ref = &binding->host;
		break;

	case HOST:
		ref = &binding->host;
		reverse_ref = &binding->guest;
		break;

	default:
		assert(0);
		return -EACCES;
	}

	substitute_path_prefix(path, ref->length, reverse_ref->path, reverse_ref->length);

	return 1;
}

/**
 * Remove @binding from all the @tracee's lists of bindings it belongs to.
 */
void remove_binding_from_all_lists(const Tracee *tracee, Binding *binding)
{
       if (IS_LINKED(binding, link.pending))
	       CIRCLEQ_REMOVE_(tracee, binding, pending);

       if (IS_LINKED(binding, link.guest))
	       CIRCLEQ_REMOVE_(tracee, binding, guest);

       if (IS_LINKED(binding, link.host))
	       CIRCLEQ_REMOVE_(tracee, binding, host);
}

/**
 * Insert @binding into the list of @bindings, in a sorted manner so
 * as to make the substitution of nested bindings determistic, ex.:
 *
 *     -b /bin:/foo/bin -b /usr/bin/more:/foo/bin/more
 *
 * Note: "nested" from the @side point-of-view.
 */
static void insort_binding(const Tracee *tracee, Side side, Binding *binding)
{
	Binding *iterator;
	Binding *previous = NULL;
	Binding *next = CIRCLEQ_FIRST(HEAD(tracee, side));

	/* Find where it should be added in the list.  */
	CIRCLEQ_FOREACH_(tracee, iterator, side) {
		Comparison comparison;
		const Path *binding_path;
		const Path *iterator_path;

		switch (side) {
		case PENDING:
		case GUEST:
			binding_path = &binding->guest;
			iterator_path = &iterator->guest;
			break;

		case HOST:
			binding_path = &binding->host;
			iterator_path = &iterator->host;
			break;

		default:
			assert(0);
			return;
		}

		comparison = compare_paths2(binding_path->path, binding_path->length,
					    iterator_path->path, iterator_path->length);
		switch (comparison) {
		case PATHS_ARE_EQUAL:
			if (side == HOST) {
				previous = iterator;
				break;
			}

			if (tracee->verbose > 0 && getenv("PROOT_IGNORE_MISSING_BINDINGS") == NULL) {
				note(tracee, WARNING, USER,
					"both '%s' and '%s' are bound to '%s', "
					"only the last binding is active.",
					iterator->host.path, binding->host.path,
					binding->guest.path);
			}

			/* Replace this iterator with the new binding.  */
			CIRCLEQ_INSERT_AFTER_(tracee, iterator, binding, side);
			remove_binding_from_all_lists(tracee, iterator);
			return;

		case PATH1_IS_PREFIX:
			/* The new binding contains the iterator.  */
			previous = iterator;
			break;

		case PATH2_IS_PREFIX:
			/* The iterator contains the new binding.
			 * Use the deepest container.  */
			if (next == (void *) HEAD(tracee, side))
				next = iterator;
			break;

		case PATHS_ARE_NOT_COMPARABLE:
			break;

		default:
			assert(0);
			return;
		}
	}

	/* Insert this binding in the list.  */
	if (previous != NULL)
		CIRCLEQ_INSERT_AFTER_(tracee, previous, binding, side);
	else if (next != (void *) HEAD(tracee, side))
		CIRCLEQ_INSERT_BEFORE_(tracee, next, binding, side);
	else
		CIRCLEQ_INSERT_HEAD_(tracee, binding, side);
}

/**
 * c.f. function above.
 */
static void insort_binding2(const Tracee *tracee, Binding *binding)
{
	binding->need_substitution =
		compare_paths(binding->host.path, binding->guest.path) != PATHS_ARE_EQUAL;

	insort_binding(tracee, GUEST, binding);
	insort_binding(tracee, HOST, binding);
}

/**
 * Create and insert a new binding (@host_path:@guest_path) into the
 * list of @tracee's bindings.  The Talloc parent of this new binding
 * is @context.  This function returns NULL if an error occurred,
 * otherwise a pointer to the newly created binding.
 */
Binding *insort_binding3(const Tracee *tracee, const TALLOC_CTX *context,
			const char host_path[PATH_MAX],
			const char guest_path[PATH_MAX])
{
	Binding *binding;

	binding = talloc_zero(context, Binding);
	if (binding == NULL)
		return NULL;

	strcpy(binding->host.path, host_path);
	strcpy(binding->guest.path, guest_path);

	binding->host.length = strlen(binding->host.path);
	binding->guest.length = strlen(binding->guest.path);

	insort_binding2(tracee, binding);

	return binding;
}

/**
 * Free all bindings from @bindings.
 *
 * Note: this is a Talloc destructor.
 */
static int remove_bindings(Bindings *bindings)
{
	Binding *binding;
	Tracee *tracee;

	/* Unlink all bindings from the @link list.  */
#define CIRCLEQ_REMOVE_ALL(name) do {				\
	binding = CIRCLEQ_FIRST(bindings);			\
	while (binding != (void *) bindings) {			\
		Binding *next = CIRCLEQ_NEXT(binding, link.name);\
		CIRCLEQ_REMOVE_(tracee, binding, name);		\
		binding = next;					\
	}							\
} while (0)

	/* Search which link is used by this list.  */
	tracee = TRACEE(bindings);
	if (bindings == tracee->fs->bindings.pending)
		CIRCLEQ_REMOVE_ALL(pending);
	else if (bindings == tracee->fs->bindings.guest)
		CIRCLEQ_REMOVE_ALL(guest);
	else if (bindings == tracee->fs->bindings.host)
		CIRCLEQ_REMOVE_ALL(host);

	bzero(bindings, sizeof(Bindings));

	return 0;
}

/**
 * Allocate a new binding "@host:@guest" and attach it to
 * @tracee->fs->bindings.pending.  This function complains about
 * missing @host path only if @must_exist is true.  This function
 * returns the allocated binding on success, NULL on error.
 */
Binding *new_binding(Tracee *tracee, const char *host, const char *guest, bool must_exist)
{
	Binding *binding;
	char base[PATH_MAX];
	int status;

	/* Lasy allocation of the list of bindings specified by the
	 * user.  This list will be used by initialize_bindings().  */
	if (tracee->fs->bindings.pending == NULL) {
		tracee->fs->bindings.pending = talloc_zero(tracee->fs, Bindings);
		if (tracee->fs->bindings.pending == NULL)
			return NULL;
		CIRCLEQ_INIT(tracee->fs->bindings.pending);
		talloc_set_destructor(tracee->fs->bindings.pending, remove_bindings);
	}

	/* Allocate an empty binding.  */
	binding = talloc_zero(tracee->ctx, Binding);
	if (binding == NULL)
		return NULL;

	/* Canonicalize the host part of the binding, as expected by
	 * get_binding().  */
	status = realpath2(tracee->reconf.tracee, binding->host.path, host, true);
	if (status < 0) {
		if (must_exist && getenv("PROOT_IGNORE_MISSING_BINDINGS") == NULL)
			note(tracee, WARNING, INTERNAL, "can't sanitize binding \"%s\": %s",
				host, strerror(-status));
		goto error;
	}
	binding->host.length = strlen(binding->host.path);

	/* Symetric binding?  */
	guest = guest ?: host;

	/* When not absolute, assume the guest path is relative to the
	 * current working directory, as with ``-b .`` for instance.  */
	if (guest[0] != '/') {
		status = getcwd2(tracee->reconf.tracee, base);
		if (status < 0) {
			note(tracee, WARNING, INTERNAL, "can't sanitize binding \"%s\": %s",
				binding->guest.path, strerror(-status));
			goto error;
		}
	}
	else
		strcpy(base, "/");

	status = join_paths(2, binding->guest.path, base, guest);
	if (status < 0) {
		note(tracee, WARNING, SYSTEM, "can't sanitize binding \"%s\"",
			binding->guest.path);
		goto error;
	}
	binding->guest.length = strlen(binding->guest.path);

	/* Keep the list of bindings specified by the user ordered,
	 * for the sake of consistency.  For instance binding to "/"
	 * has to be the last in the list.  */
	insort_binding(tracee, PENDING, binding);

	return binding;

error:
	TALLOC_FREE(binding);
	return NULL;
}

/**
 * Canonicalize the guest part of the given @binding, insert it into
 * @tracee->fs->bindings.guest and @tracee->fs->bindings.host.  This
 * function returns -1 if an error occured, 0 otherwise.
 */
static void initialize_binding(Tracee *tracee, Binding *binding)
{
	char path[PATH_MAX];
	struct stat statl;
	int status;

	/* All bindings but "/" must be canonicalized.  The exception
	 * for "/" is required to bootstrap the canonicalization.  */
	if (compare_paths(binding->guest.path, "/") != PATHS_ARE_EQUAL) {
		bool dereference;
		size_t length;

		strcpy(path, binding->guest.path);
		length = strlen(path);
		assert(length > 0);

		/* Does the user explicitly tell not to dereference
		 * guest path?  */
		dereference = (path[length - 1] != '!');
		if (!dereference)
			path[length - 1] = '\0';

		/* Initial state before canonicalization.  */
		strcpy(binding->guest.path, "/");

		/* Remember the type of the final component, it will
		 * be used in build_glue() later.  */
		status = lstat(binding->host.path, &statl);
		tracee->glue_type = (status < 0 || S_ISBLK(statl.st_mode) || S_ISCHR(statl.st_mode)
				? S_IFREG : statl.st_mode & S_IFMT);

		/* Sanitize the guest path of the binding within the
		   alternate rootfs since it is assumed by
		   substitute_binding().  */
		status = canonicalize(tracee, path, dereference, binding->guest.path, 0);
		if (status < 0) {
			note(tracee, WARNING, INTERNAL,
				"sanitizing the guest path (binding) \"%s\": %s",
				path, strerror(-status));
			return;
		}

		/* Remove the trailing "/" or "/." as expected by
		 * substitute_binding().  */
		chop_finality(binding->guest.path);

		/* Disable definitively the creation of the glue for
		 * this binding.  */
		tracee->glue_type = 0;
	}

	binding->guest.length = strlen(binding->guest.path);

	insort_binding2(tracee, binding);
}

/**
 * Add bindings induced by @new_binding when @tracee is being sub-reconfigured.
 * For example, if the previous configuration ("-r /rootfs1") contains this
 * binding:
 *
 *      -b /home/ced:/usr/local/ced
 *
 * and if the current configuration ("-r /rootfs2") introduces such a new
 * binding:
 *
 *      -b /usr:/media
 *
 * then the following binding is induced:
 *
 *      -b /home/ced:/media/local/ced
 */
static void add_induced_bindings(Tracee *tracee, const Binding *new_binding)
{
	Binding *old_binding;
	char path[PATH_MAX];
	int status;

	/* Only for reconfiguration.  */
	if (tracee->reconf.tracee == NULL)
		return;

	/* From the example, PRoot has already converted "-b /usr:/media" into
	 * "-b /rootfs1/usr:/media" in order to ensure the host part is really a
	 * host path.  Here, the host part is converted back to "/usr" since the
	 * comparison can't be made on "/rootfs1/usr".
	 */
	strcpy(path, new_binding->host.path);
	status = detranslate_path(tracee->reconf.tracee, path, NULL);
	if (status < 0)
		return;

	CIRCLEQ_FOREACH_(tracee->reconf.tracee, old_binding, GUEST) {
		Binding *induced_binding;
		Comparison comparison;
		char path2[PATH_MAX];
		size_t prefix_length;

		/* Check if there's an induced binding by searching a common
		 * path prefix in between new/old bindings:
		 *
		 *   -b /home/ced:[/usr]/local/ced
		 *   -b [/usr]:/media
		 */
		comparison = compare_paths(path, old_binding->guest.path);
		if (comparison != PATH1_IS_PREFIX)
			continue;

		/* Convert the path of this induced binding to the new
		 * filesystem namespace.  From the example, "/usr/local/ced" is
		 * converted into "/media/local/ced".  Note: substitute_binding
		 * can't be used in this case since it would expect
		 * "/rootfs1/usr/local/ced instead".
		 */
		prefix_length = strlen(path);
		if (prefix_length == 1)
			prefix_length = 0;

		status = join_paths(2, path2, new_binding->guest.path, old_binding->guest.path + prefix_length);
		if (status < 0)
			continue;

		/* Install the induced binding.  From the example:
		 *
		 *     -b /home/ced:/media/local/ced
		 */
		induced_binding = talloc_zero(tracee->ctx, Binding);
		if (induced_binding == NULL)
			continue;

		strcpy(induced_binding->host.path, old_binding->host.path);
		strcpy(induced_binding->guest.path, path2);

		induced_binding->host.length = strlen(induced_binding->host.path);
		induced_binding->guest.length = strlen(induced_binding->guest.path);

		VERBOSE(tracee, 2, "induced binding: %s:%s (old) & %s:%s (new) -> %s:%s (induced)",
			old_binding->host.path, old_binding->guest.path, path, new_binding->guest.path,
			induced_binding->host.path, induced_binding->guest.path);

		insort_binding2(tracee, induced_binding);
	}
}

/**
 * Allocate @tracee->fs->bindings.guest and
 * @tracee->fs->bindings.host, then call initialize_binding() on each
 * binding listed in @tracee->fs->bindings.pending.
 */
int initialize_bindings(Tracee *tracee)
{
	Binding *binding;

	/* Sanity checks.  */
	assert(get_root(tracee) != NULL);
	assert(tracee->fs->bindings.pending != NULL);
	assert(tracee->fs->bindings.guest == NULL);
	assert(tracee->fs->bindings.host == NULL);

	/* Allocate @tracee->fs->bindings.guest and
	 * @tracee->fs->bindings.host.  */
	tracee->fs->bindings.guest = talloc_zero(tracee->fs, Bindings);
	tracee->fs->bindings.host  = talloc_zero(tracee->fs, Bindings);
	if (tracee->fs->bindings.guest == NULL || tracee->fs->bindings.host == NULL) {
		note(tracee, ERROR, INTERNAL, "can't allocate enough memory");
		TALLOC_FREE(tracee->fs->bindings.guest);
		TALLOC_FREE(tracee->fs->bindings.host);
		return -1;
	}

	CIRCLEQ_INIT(tracee->fs->bindings.guest);
	CIRCLEQ_INIT(tracee->fs->bindings.host);

	talloc_set_destructor(tracee->fs->bindings.guest, remove_bindings);
	talloc_set_destructor(tracee->fs->bindings.host, remove_bindings);

	/* The binding to "/" has to be installed before other
	 * bindings since this former is required to canonicalize
	 * these latters.  */
	binding = CIRCLEQ_LAST(tracee->fs->bindings.pending);
	assert(compare_paths(binding->guest.path, "/") == PATHS_ARE_EQUAL);

	/* Call initialize_binding() on each pending binding in
	 * reverse order: the last binding "/" is used to bootstrap
	 * the canonicalization.  */
	while (binding != (void *) tracee->fs->bindings.pending) {
		Binding *previous;
		previous = CIRCLEQ_PREV(binding, link.pending);

		/* Canonicalize then insert this binding into
		 * tracee->fs->bindings.guest/host.  */
		initialize_binding(tracee, binding);

		/* Add induced bindings on sub-reconfiguration.  */
		add_induced_bindings(tracee, binding);

		binding = previous;
	}

	TALLOC_FREE(tracee->fs->bindings.pending);

	if (tracee->verbose > 0)
		print_bindings(tracee);

	return 0;
}