context BUGFIX store pointers to leafref link records (#2379)

This patch fixes segfaults caused by invalid memory read during leafref
links removal process. It is tight hash_table implementation, as
hash_table removal of record can invalidate all other record pointers
due to memory reallocation process

Author: steweg

src/context.c

@@ -272,9 +272,9 @@ ly_ctx_ht_err_equal_cb(void *val1_p, void *val2_p, ly_bool UNUSED(mod), void *UN
 static ly_bool
 ly_ctx_ht_leafref_links_equal_cb(void *val1_p, void *val2_p, ly_bool UNUSED(mod), void *UNUSED(cb_data))
 {
-    struct lyd_leafref_links_rec *rec1 = val1_p, *rec2 = val2_p;
+    struct lyd_leafref_links_rec **rec1 = val1_p, **rec2 = val2_p;
 
-    return rec1->node == rec2->node;
+    return (*rec1)->node == (*rec2)->node;
 }
 
 /**
@@ -285,9 +285,10 @@ ly_ctx_ht_leafref_links_equal_cb(void *val1_p, void *val2_p, ly_bool UNUSED(mod)
 static void
 ly_ctx_ht_leafref_links_rec_free(void *val_p)
 {
-    struct lyd_leafref_links_rec *rec = val_p;
+    struct lyd_leafref_links_rec **rec = val_p;
 
-    lyd_free_leafref_links_rec(rec);
+    lyd_free_leafref_links_rec(*rec);
+    free(*rec);
 }
 
 LIBYANG_API_DEF LY_ERR
@@ -316,7 +317,12 @@ ly_ctx_new(const char *search_dir, uint16_t options, struct ly_ctx **new_ctx)
     LY_CHECK_ERR_GOTO(lyplg_init(builtin_plugins_only), LOGINT(NULL); rc = LY_EINT, cleanup);
 
     if (options & LY_CTX_LEAFREF_LINKING) {
-        ctx->leafref_links_ht = lyht_new(1, sizeof(struct lyd_leafref_links_rec), ly_ctx_ht_leafref_links_equal_cb, NULL, 1);
+        /**
+         * storing the pointer instead of record itself is needed to avoid invalid memory reads. Hash table can reallocate
+         * its memory completely during various manipulation function (e.g. remove, insert). In case of using pointers, the
+         * pointer can be reallocated safely, while record itself remains untouched and can be accessed/modified freely
+         * */
+        ctx->leafref_links_ht = lyht_new(1, sizeof(struct lyd_leafref_links_rec *), ly_ctx_ht_leafref_links_equal_cb, NULL, 1);
         LY_CHECK_ERR_GOTO(!ctx->leafref_links_ht, rc = LY_EMEM, cleanup);
     }
 
@@ -654,7 +660,7 @@ ly_ctx_set_options(struct ly_ctx *ctx, uint16_t option)
     }
 
     if (!(ctx->flags & LY_CTX_LEAFREF_LINKING) && (option & LY_CTX_LEAFREF_LINKING)) {
-        ctx->leafref_links_ht = lyht_new(1, sizeof(struct lyd_leafref_links_rec), ly_ctx_ht_leafref_links_equal_cb, NULL, 1);
+        ctx->leafref_links_ht = lyht_new(1, sizeof(struct lyd_leafref_links_rec *), ly_ctx_ht_leafref_links_equal_cb, NULL, 1);
         LY_CHECK_ERR_RET(!ctx->leafref_links_ht, LOGARG(ctx, option), LY_EMEM);
     }
 

src/tree_data.c

@@ -3626,8 +3626,11 @@ LY_ERR
 lyd_get_or_create_leafref_links_record(const struct lyd_node_term *node, struct lyd_leafref_links_rec **record, ly_bool create)
 {
     struct ly_ht *ht;
+    LY_ERR ret = LY_SUCCESS;
     uint32_t hash;
     struct lyd_leafref_links_rec rec = {0};
+    struct lyd_leafref_links_rec *rec_p = &rec;
+    struct lyd_leafref_links_rec **rec_p2;
 
     assert(node);
     assert(record);
@@ -3642,15 +3645,23 @@ lyd_get_or_create_leafref_links_record(const struct lyd_node_term *node, struct
     ht = LYD_CTX(node)->leafref_links_ht;
     hash = lyht_hash((const char *)&node, sizeof node);
 
-    if (lyht_find(ht, &rec, hash, (void **)record) == LY_ENOTFOUND) {
+    if (lyht_find(ht, &rec_p, hash, (void **)&rec_p2) == LY_ENOTFOUND) {
         if (create) {
-            LY_CHECK_RET(lyht_insert_no_check(ht, &rec, hash, (void **)record));
+            rec_p = calloc(1, sizeof rec);
+            rec_p->node = node;
+            LY_CHECK_ERR_RET(!rec_p, LOGMEM(LYD_CTX(node)), LY_EMEM);
+            ret = lyht_insert_no_check(ht, &rec_p, hash, (void **)&rec_p2);
+            LY_CHECK_ERR_GOTO(ret, free(rec_p), cleanup);
         } else {
             return LY_ENOTFOUND;
         }
     }
 
-    return LY_SUCCESS;
+cleanup:
+    if (!ret) {
+        *record = *rec_p2;
+    }
+    return ret;
 }
 
 LIBYANG_API_DEF LY_ERR

src/tree_data_free.c

@@ -191,7 +191,8 @@ lyd_free_leafref_nodes(const struct lyd_node_term *node)
     /* free entry itself from hash table */
     ht = LYD_CTX(node)->leafref_links_ht;
     hash = lyht_hash((const char *)&node, sizeof node);
-    lyht_remove(ht, rec, hash);
+    lyht_remove(ht, &rec, hash);
+    free(rec);
 }
 
 /**