Fuzz target for bracketed patterns, such as [[[[x]]]]

fuzz/CMakeLists.txt

@@ -19,3 +19,4 @@ macro(fuzzer name)
 endmacro()
 
 fuzzer(fuzz_quadratic)
+fuzzer(fuzz_quadratic_brackets)

fuzz/fuzz_quadratic_brackets.c

@@ -0,0 +1,108 @@
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include "cmark-gfm.h"
+#include "cmark-gfm-core-extensions.h"
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+const char *extension_names[] = {
+  "autolink",
+  "strikethrough",
+  "table",
+  "tagfilter",
+  NULL,
+};
+
+int LLVMFuzzerInitialize(int *argc, char ***argv) {
+  cmark_gfm_core_extensions_ensure_registered();
+  return 0;
+}
+
+int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
+  struct __attribute__((packed)) {
+    int options;
+    int width;
+    uint8_t startlen;
+    uint8_t openlen;
+    uint8_t middlelen;
+    uint8_t closelen;
+  } fuzz_config;
+
+  if (size >= sizeof(fuzz_config)) {
+    /* The beginning of `data` is treated as fuzzer configuration */
+    memcpy(&fuzz_config, data, sizeof(fuzz_config));
+
+    /* Test options that are used by GitHub. */
+    fuzz_config.options = CMARK_OPT_UNSAFE | CMARK_OPT_FOOTNOTES | CMARK_OPT_GITHUB_PRE_LANG | CMARK_OPT_HARDBREAKS;
+    fuzz_config.openlen = fuzz_config.openlen & 0x7;
+    fuzz_config.middlelen = fuzz_config.middlelen & 0x7;
+    fuzz_config.closelen = fuzz_config.closelen & 0x7;
+
+    /* Remainder of input is the markdown */
+    const char *markdown0 = (const char *)(data + sizeof(fuzz_config));
+    const size_t markdown_size0 = size - sizeof(fuzz_config);
+    char markdown[0x80000];
+    if (markdown_size0 <= sizeof(markdown)) {
+      size_t markdown_size = 0;
+      const size_t componentslen = fuzz_config.startlen + fuzz_config.openlen + fuzz_config.middlelen + fuzz_config.closelen;
+      if (componentslen <= markdown_size0) {
+        size_t offset = 0;
+        const size_t endlen = markdown_size0 - componentslen;
+        memcpy(&markdown[markdown_size], &markdown0[offset], fuzz_config.startlen);
+        markdown_size += fuzz_config.startlen;
+        offset += fuzz_config.startlen;
+
+        if (0 < fuzz_config.openlen) {
+          while (markdown_size + fuzz_config.openlen <= sizeof(markdown)/2) {
+            memcpy(&markdown[markdown_size], &markdown0[offset],
+                   fuzz_config.openlen);
+            markdown_size += fuzz_config.openlen;
+          }
+          offset += fuzz_config.openlen;
+        }
+        memcpy(&markdown[markdown_size], &markdown0[offset],
+               fuzz_config.middlelen);
+        markdown_size += fuzz_config.middlelen;
+        offset += fuzz_config.middlelen;
+        if (0 < fuzz_config.closelen) {
+          while (markdown_size + fuzz_config.closelen + endlen <= sizeof(markdown)) {
+            memcpy(&markdown[markdown_size], &markdown0[offset],
+                   fuzz_config.closelen);
+            markdown_size += fuzz_config.closelen;
+          }
+          offset += fuzz_config.closelen;
+        }
+        memcpy(&markdown[markdown_size], &markdown0[offset],
+               endlen);
+        markdown_size += endlen;
+      } else {
+        markdown_size = markdown_size0;
+        memcpy(markdown, markdown0, markdown_size);
+      }
+
+      cmark_parser *parser = cmark_parser_new(fuzz_config.options);
+
+      for (const char **it = extension_names; *it; ++it) {
+        const char *extension_name = *it;
+        cmark_syntax_extension *syntax_extension = cmark_find_syntax_extension(extension_name);
+        if (!syntax_extension) {
+          fprintf(stderr, "%s is not a valid syntax extension\n", extension_name);
+          abort();
+        }
+        cmark_parser_attach_syntax_extension(parser, syntax_extension);
+      }
+
+      cmark_parser_feed(parser, markdown, markdown_size);
+      cmark_node *doc = cmark_parser_finish(parser);
+
+      free(cmark_render_html(doc, fuzz_config.options, NULL));
+
+      cmark_node_free(doc);
+      cmark_parser_free(parser);
+    }
+  }
+  return 0;
+}