[tracker-miners/sam/blocklist-dds: 2/3] Allow blocklisting certain MIME types in tracker-extract rules

[Sam Thursfield <sthursfield src gnome org>]

commit cc6293bde4085a3654a5c22da12cfa2983a82605
Author: Sam Thursfield <sam afuera me uk>
Date:   Sun Nov 3 18:12:13 2019 +0100

    Allow blocklisting certain MIME types in tracker-extract rules
    
    The initial use case for this is solving
    https://gitlab.gnome.org/GNOME/tracker/issues/158 -- we need to block
    .dds files from being extracted, as they can trigger arbitrary incorrect
    codepaths in GStreamer that sometimes cause Linux to hang.

 src/libtracker-extract/tracker-module-manager.c    | 51 +++++++++++++++++-----
 .../test-extract-rules/90-image-generic.rule       |  3 +-
 .../tracker-module-manager-test.c                  |  4 ++
 3 files changed, 45 insertions(+), 13 deletions(-)
---
diff --git a/src/libtracker-extract/tracker-module-manager.c b/src/libtracker-extract/tracker-module-manager.c
index 426cfb385..b62f90b16 100644
--- a/src/libtracker-extract/tracker-module-manager.c
+++ b/src/libtracker-extract/tracker-module-manager.c
@@ -30,7 +30,8 @@
 typedef struct {
        const gchar *rule_path;
        const gchar *module_path; /* intern string */
-       GList *patterns;
+       GList *allow_patterns;
+       GList *block_patterns;
        GStrv fallback_rdf_types;
 } RuleInfo;
 
@@ -71,8 +72,8 @@ load_extractor_rule (GKeyFile    *key_file,
                      GError     **error)
 {
        GError *local_error = NULL;
-       gchar *module_path, **mimetypes;
-       gsize n_mimetypes, i;
+       gchar *module_path, **allow_mimetypes, **block_mimetypes;
+       gsize n_allow_mimetypes, n_block_mimetypes, i;
        RuleInfo rule = { 0 };
 
        module_path = g_key_file_get_string (key_file, "ExtractorRule", "ModulePath", &local_error);
@@ -104,9 +105,9 @@ load_extractor_rule (GKeyFile    *key_file,
                module_path = tmp;
        }
 
-       mimetypes = g_key_file_get_string_list (key_file, "ExtractorRule", "MimeTypes", &n_mimetypes, 
&local_error);
+       allow_mimetypes = g_key_file_get_string_list (key_file, "ExtractorRule", "MimeTypes", 
&n_allow_mimetypes, &local_error);
 
-       if (!mimetypes) {
+       if (!allow_mimetypes) {
                g_free (module_path);
 
                if (local_error) {
@@ -116,6 +117,10 @@ load_extractor_rule (GKeyFile    *key_file,
                return FALSE;
        }
 
+       /* This key is optional */
+       block_mimetypes = g_key_file_get_string_list (key_file, "ExtractorRule", "BlockMimeTypes", 
&n_block_mimetypes, &local_error);
+       g_debug("Block mimetypes for %s: %i", rule_path, n_block_mimetypes);
+
        rule.rule_path = g_strdup (rule_path);
 
        rule.fallback_rdf_types = g_key_file_get_string_list (key_file, "ExtractorRule", "FallbackRdfTypes", 
NULL, NULL);
@@ -123,15 +128,23 @@ load_extractor_rule (GKeyFile    *key_file,
        /* Construct the rule */
        rule.module_path = g_intern_string (module_path);
 
-       for (i = 0; i < n_mimetypes; i++) {
+       for (i = 0; i < n_allow_mimetypes; i++) {
+               GPatternSpec *pattern;
+
+               pattern = g_pattern_spec_new (allow_mimetypes[i]);
+               rule.allow_patterns = g_list_prepend (rule.allow_patterns, pattern);
+       }
+
+       for (i = 0; i < n_block_mimetypes; i++) {
                GPatternSpec *pattern;
 
-               pattern = g_pattern_spec_new (mimetypes[i]);
-               rule.patterns = g_list_prepend (rule.patterns, pattern);
+               pattern = g_pattern_spec_new (block_mimetypes[i]);
+               rule.block_patterns = g_list_prepend (rule.block_patterns, pattern);
        }
 
        g_array_append_val (rules, rule);
-       g_strfreev (mimetypes);
+       g_strfreev (allow_mimetypes);
+       g_strfreev (block_mimetypes);
        g_free (module_path);
 
        return TRUE;
@@ -245,15 +258,29 @@ lookup_rules (const gchar *mimetype)
        /* Apply the rules! */
        for (i = 0; i < rules->len; i++) {
                GList *l;
+               gboolean matched_allow_pattern = FALSE, matched_block_pattern = FALSE;
 
                info = &g_array_index (rules, RuleInfo, i);
 
-               for (l = info->patterns; l; l = l->next) {
+               for (l = info->allow_patterns; l; l = l->next) {
                        if (g_pattern_match (l->data, len, mimetype, reversed)) {
-                               /* Match, store for future queries and return */
-                               mimetype_rules = g_list_prepend (mimetype_rules, info);
+                               g_debug ("%s: Matched on allow pattern", mimetype);
+                               matched_allow_pattern = TRUE;
+                               break;
                        }
                }
+
+               for (l = info->block_patterns; l; l = l->next) {
+                       if (g_pattern_match (l->data, len, mimetype, reversed)) {
+                               g_debug ("%s: Matched on block pattern", mimetype);
+                               matched_block_pattern = TRUE;
+                               break;
+                       }
+               }
+
+               if (matched_allow_pattern && !matched_block_pattern) {
+                       mimetype_rules = g_list_prepend (mimetype_rules, info);
+               };
        }
 
        if (mimetype_rules) {
diff --git a/tests/libtracker-extract/test-extract-rules/90-image-generic.rule 
b/tests/libtracker-extract/test-extract-rules/90-image-generic.rule
index 642c3e0da..e34c6b3dc 100644
--- a/tests/libtracker-extract/test-extract-rules/90-image-generic.rule
+++ b/tests/libtracker-extract/test-extract-rules/90-image-generic.rule
@@ -1,4 +1,5 @@
 [ExtractorRule]
-ModulePath=libextract-gstreamer.so
+ModulePath=TEST_MODULE_IMAGE
 MimeTypes=image/*;
+BlockMimeTypes=image/x-blocked;
 FallbackRdfTypes=nfo:Image;nmm:Photo;
diff --git a/tests/libtracker-extract/tracker-module-manager-test.c 
b/tests/libtracker-extract/tracker-module-manager-test.c
index ffd2a39b2..992f6ee75 100644
--- a/tests/libtracker-extract/tracker-module-manager-test.c
+++ b/tests/libtracker-extract/tracker-module-manager-test.c
@@ -67,6 +67,10 @@ test_extract_rules (void)
        // No rule should match this.
        l = tracker_extract_module_manager_get_matching_rules("text/generic");
        g_assert_cmpint (g_list_length (l), ==, 0);
+
+       // The image/x-blocked MIME type is explicitly blocked, so no rule should match.
+       l = tracker_extract_module_manager_get_matching_rules("image/x-blocked");
+       g_assert_cmpint (g_list_length (l), ==, 0);
 }
 
 int