Add a hard link detecting/filtering directory iterator

The reason this is implemented separately, instead of roling it into
the recursive iterator, is so that we can do additional filtering
in between. For instance, we can rewrite the path and the hard link
path will match up, or if we remove nodes from the hierarchy, we
won't end up with a hard link pointing outside.

Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>

1 files changed, 245 insertions, 0 deletions

diff --git a/lib/sqfs/src/io/dir_hl.c b/lib/sqfs/src/io/dir_hl.c
new file mode 100644
index 0000000..08efaaf
--- /dev/null
+++ b/lib/sqfs/src/io/dir_hl.c
@@ -0,0 +1,245 @@
+/* SPDX-License-Identifier: LGPL-3.0-or-later */
+/*
+ * dir_hl.c
+ *
+ * Copyright (C) 2023 David Oberhollenzer <goliath@infraroot.at>
+ */
+#define SQFS_BUILDING_DLL
+#include "config.h"
+
+#include "util/util.h"
+#include "util/rbtree.h"
+#include "compat.h"
+
+#include "sqfs/dir_entry.h"
+#include "sqfs/error.h"
+#include "sqfs/inode.h"
+#include "sqfs/io.h"
+
+#include <stdlib.h>
+#include <string.h>
+
+typedef struct {
+	sqfs_u64 dev;
+	sqfs_u64 inum;
+} inumtree_key_t;
+
+typedef struct {
+	sqfs_dir_iterator_t base;
+
+	int state;
+	const char *link_target;
+	sqfs_dir_iterator_t *src;
+	rbtree_t inumtree;
+} hl_iterator_t;
+
+static int compare_inum(const void *ctx, const void *lhs, const void *rhs)
+{
+	const inumtree_key_t *l = (const inumtree_key_t *)lhs;
+	const inumtree_key_t *r = (const inumtree_key_t *)rhs;
+	(void)ctx;
+
+	if (l->dev != r->dev)
+		return l->dev < r->dev ? -1 : 1;
+
+	return l->inum < r->inum ? -1 : (l->inum > r->inum ? 1 : 0);
+}
+
+static const char *detect_hard_link(const hl_iterator_t *it,
+				    const sqfs_dir_entry_t *ent)
+{
+	inumtree_key_t key = { ent->dev, ent->inode };
+	rbtree_node_t *tn;
+
+	if (S_ISDIR(ent->mode))
+		return NULL;
+
+	tn = rbtree_lookup(&(it->inumtree), &key);
+	if (tn == NULL)
+		return NULL;
+
+	return *((const char **)rbtree_node_value(tn));
+}
+
+static int store_hard_link(hl_iterator_t *it,
+			   const sqfs_dir_entry_t *ent)
+{
+	inumtree_key_t key = { ent->dev, ent->inode };
+	char *target;
+	int ret;
+
+	if (S_ISDIR(ent->mode) || (ent->flags & SQFS_DIR_ENTRY_FLAG_HARD_LINK))
+		return 0;
+
+	target = strdup(ent->name);
+	if (target == NULL)
+		return SQFS_ERROR_ALLOC;
+
+	ret = rbtree_insert(&(it->inumtree), &key, &target);
+	if (ret != 0)
+		free(target);
+
+	return ret;
+}
+
+static void remove_links(rbtree_node_t *n)
+{
+	if (n != NULL) {
+		char **lnk = rbtree_node_value(n);
+		free(*lnk);
+		*lnk = NULL;
+
+		remove_links(n->left);
+		remove_links(n->right);
+	}
+}
+
+/*****************************************************************************/
+
+static void destroy(sqfs_object_t *obj)
+{
+	hl_iterator_t *it = (hl_iterator_t *)obj;
+
+	remove_links(it->inumtree.root);
+	rbtree_cleanup(&it->inumtree);
+	sqfs_drop(it->src);
+	free(it);
+}
+
+static int next(sqfs_dir_iterator_t *base, sqfs_dir_entry_t **out)
+{
+	hl_iterator_t *it = (hl_iterator_t *)base;
+	int ret;
+
+	if (it->state != 0) {
+		*out = NULL;
+		return it->state;
+	}
+
+	ret = it->src->next(it->src, out);
+	if (ret != 0) {
+		*out = NULL;
+		it->link_target = NULL;
+		it->state = ret;
+		return ret;
+	}
+
+	it->link_target = detect_hard_link(it, *out);
+
+	if (it->link_target == NULL) {
+		ret = store_hard_link(it, *out);
+		if (ret != 0) {
+			it->state = ret;
+			sqfs_free(*out);
+			*out = NULL;
+		}
+	} else {
+		(*out)->mode = SQFS_INODE_MODE_LNK | 0777;
+		(*out)->flags |= SQFS_DIR_ENTRY_FLAG_HARD_LINK;
+	}
+
+	return ret;
+}
+
+static int read_link(sqfs_dir_iterator_t *base, char **out)
+{
+	hl_iterator_t *it = (hl_iterator_t *)base;
+
+	if (it->link_target != NULL) {
+		*out = strdup(it->link_target);
+		if (*out == NULL)
+			return SQFS_ERROR_ALLOC;
+		return 0;
+	}
+
+	if (it->state != 0)
+		return SQFS_ERROR_NO_ENTRY;
+
+	return it->src->read_link(it->src, out);
+}
+
+static int open_subdir(sqfs_dir_iterator_t *base, sqfs_dir_iterator_t **out)
+{
+	hl_iterator_t *it = (hl_iterator_t *)base;
+
+	if (it->link_target != NULL) {
+		*out = NULL;
+		return SQFS_ERROR_NOT_DIR;
+	}
+
+	if (it->state != 0)
+		return SQFS_ERROR_NO_ENTRY;
+
+	return it->src->open_subdir(it->src, out);
+}
+
+static void ignore_subdir(sqfs_dir_iterator_t *base)
+{
+	hl_iterator_t *it = (hl_iterator_t *)base;
+
+	if (it->link_target == NULL && it->state == 0)
+		it->src->ignore_subdir(it->src);
+}
+
+static int open_file_ro(sqfs_dir_iterator_t *base, sqfs_istream_t **out)
+{
+	hl_iterator_t *it = (hl_iterator_t *)base;
+
+	if (it->link_target != NULL) {
+		*out = NULL;
+		return SQFS_ERROR_NOT_FILE;
+	}
+
+	if (it->state != 0)
+		return SQFS_ERROR_NO_ENTRY;
+
+	return it->src->open_file_ro(it->src, out);
+}
+
+static int read_xattr(sqfs_dir_iterator_t *base, sqfs_xattr_t **out)
+{
+	hl_iterator_t *it = (hl_iterator_t *)base;
+
+	if (it->link_target != NULL) {
+		*out = NULL;
+		return 0;
+	}
+
+	if (it->state != 0)
+		return SQFS_ERROR_NO_ENTRY;
+
+	return it->src->read_xattr(it->src, out);
+}
+
+int sqfs_hard_link_filter_create(sqfs_dir_iterator_t **out,
+				 sqfs_dir_iterator_t *base)
+{
+	hl_iterator_t *it;
+	int ret;
+
+	*out = NULL;
+
+	it = calloc(1, sizeof(*it));
+	if (it == NULL)
+		return SQFS_ERROR_ALLOC;
+
+	ret = rbtree_init(&it->inumtree, sizeof(inumtree_key_t),
+			  sizeof(char *), compare_inum);
+	if (ret != 0) {
+		free(it);
+		return ret;
+	}
+
+	sqfs_object_init(it, destroy, NULL);
+	((sqfs_dir_iterator_t *)it)->next = next;
+	((sqfs_dir_iterator_t *)it)->read_link = read_link;
+	((sqfs_dir_iterator_t *)it)->open_subdir = open_subdir;
+	((sqfs_dir_iterator_t *)it)->ignore_subdir = ignore_subdir;
+	((sqfs_dir_iterator_t *)it)->open_file_ro = open_file_ro;
+	((sqfs_dir_iterator_t *)it)->read_xattr = read_xattr;
+
+	it->src = sqfs_grab(base);
+
+	*out = (sqfs_dir_iterator_t *)it;
+	return 0;
+}