Merge pull request from GHSA-c944-cv5f-hpvr

 Improve performance in postprocess_text

Author: anticomputer

extensions/autolink.c

@@ -269,14 +269,20 @@ static cmark_node *match(cmark_syntax_extension *ext, cmark_parser *parser,
   // inline was finished in inlines.c.
 }
 
-static bool validate_protocol(char protocol[], uint8_t *data, int rewind) {
+static bool validate_protocol(char protocol[], uint8_t *data, int rewind, int max_rewind) {
   size_t len = strlen(protocol);
 
+  if (len > (size_t)(max_rewind - rewind)) {
+    return false;
+  }
+
   // Check that the protocol matches
-  for (int i = 1; i <= len; i++) {
-    if (data[-rewind - i] != protocol[len - i]) {
-      return false;
-    }
+  if (memcmp(data - rewind - len, protocol, len) != 0) {
+    return false;
+  }
+
+  if (len == (size_t)(max_rewind - rewind)) {
+    return true;
   }
 
   char prev_char = data[-rewind - len - 1];
@@ -285,126 +291,145 @@ static bool validate_protocol(char protocol[], uint8_t *data, int rewind) {
   return !cmark_isalnum(prev_char);
 }
 
-static void postprocess_text(cmark_parser *parser, cmark_node *text, int offset, int depth) {
-  // postprocess_text can recurse very deeply if there is a very long line of
-  // '@' only.  Stop at a reasonable depth to ensure it cannot crash.
-  if (depth > 1000) return;
+static void postprocess_text(cmark_parser *parser, cmark_node *text) {
+  size_t start = 0;
+  size_t offset = 0;
+  // `text` is going to be split into a list of nodes containing shorter segments
+  // of text, so we detach the memory buffer from text and use `cmark_chunk_dup` to
+  // create references to it. Later, `cmark_chunk_to_cstr` is used to convert
+  // the references into allocated buffers. The detached buffer is freed before we
+  // return.
+  cmark_chunk detached_chunk = text->as.literal;
+  text->as.literal = cmark_chunk_dup(&detached_chunk, 0, detached_chunk.len);
+
+  uint8_t *data = text->as.literal.data;
+  size_t remaining = text->as.literal.len;
+
+  while (true) {
+    size_t link_end;
+    uint8_t *at;
+    bool auto_mailto = true;
+    bool is_xmpp = false;
+    size_t rewind;
+    size_t max_rewind;
+    size_t np = 0;
+
+    if (offset >= remaining)
+      break;
 
-  size_t link_end;
-  uint8_t *data = text->as.literal.data,
-    *at;
-  size_t size = text->as.literal.len;
-  bool auto_mailto = true;
-  bool is_xmpp = false;
-  int rewind, max_rewind,
-      nb = 0, np = 0, ns = 0;
+    at = (uint8_t *)memchr(data + start + offset, '@', remaining - offset);
+    if (!at)
+      break;
 
-  if (offset < 0 || (size_t)offset >= size)
-    return;
+    max_rewind = at - (data + start + offset);
 
-  data += offset;
-  size -= offset;
+found_at:
+    for (rewind = 0; rewind < max_rewind; ++rewind) {
+      uint8_t c = data[start + offset + max_rewind - rewind - 1];
 
-  at = (uint8_t *)memchr(data, '@', size);
-  if (!at)
-    return;
+      if (cmark_isalnum(c))
+        continue;
 
-  max_rewind = (int)(at - data);
-  data += max_rewind;
-  size -= max_rewind;
+      if (strchr(".+-_", c) != NULL)
+        continue;
 
-  for (rewind = 0; rewind < max_rewind; ++rewind) {
-    uint8_t c = data[-rewind - 1];
+      if (strchr(":", c) != NULL) {
+        if (validate_protocol("mailto:", data + start + offset + max_rewind, rewind, max_rewind)) {
+          auto_mailto = false;
+          continue;
+        }
+
+        if (validate_protocol("xmpp:", data + start + offset + max_rewind, rewind, max_rewind)) {
+          auto_mailto = false;
+          is_xmpp = true;
+          continue;
+        }
+      }
 
-    if (cmark_isalnum(c))
-      continue;
+      break;
+    }
 
-    if (strchr(".+-_", c) != NULL)
+    if (rewind == 0) {
+      offset += max_rewind + 1;
       continue;
+    }
+
+    assert(data[start + offset + max_rewind] == '@');
+    for (link_end = 1; link_end < remaining - offset - max_rewind; ++link_end) {
+      uint8_t c = data[start + offset + max_rewind + link_end];
 
-    if (strchr(":", c) != NULL) {
-      if (validate_protocol("mailto:", data, rewind)) {
-        auto_mailto = false;
+      if (cmark_isalnum(c))
         continue;
-      }
 
-      if (validate_protocol("xmpp:", data, rewind)) {
-        auto_mailto = false;
-        is_xmpp = true;
+      if (c == '@') {
+        // Found another '@', so go back and try again with an updated offset and max_rewind.
+        offset += max_rewind + 1;
+        max_rewind = link_end - 1;
+        goto found_at;
+      } else if (c == '.' && link_end < remaining - offset - max_rewind - 1 &&
+               cmark_isalnum(data[start + offset + max_rewind + link_end + 1]))
+        np++;
+      else if (c == '/' && is_xmpp)
         continue;
-      }
+      else if (c != '-' && c != '_')
+        break;
     }
 
-    break;
-  }
-
-  if (rewind == 0 || ns > 0) {
-    postprocess_text(parser, text, max_rewind + 1 + offset, depth + 1);
-    return;
-  }
-
-  for (link_end = 0; link_end < size; ++link_end) {
-    uint8_t c = data[link_end];
-
-    if (cmark_isalnum(c))
-      continue;
-
-    if (c == '@')
-      nb++;
-    else if (c == '.' && link_end < size - 1 && cmark_isalnum(data[link_end + 1]))
-      np++;
-    else if (c == '/' && is_xmpp)
+    if (link_end < 2 || np == 0 ||
+        (!cmark_isalpha(data[start + offset + max_rewind + link_end - 1]) &&
+         data[start + offset + max_rewind + link_end - 1] != '.')) {
+      offset += max_rewind + link_end;
       continue;
-    else if (c != '-' && c != '_')
-      break;
-  }
+    }
 
-  if (link_end < 2 || nb != 1 || np == 0 ||
-      (!cmark_isalpha(data[link_end - 1]) && data[link_end - 1] != '.')) {
-    postprocess_text(parser, text, max_rewind + 1 + offset, depth + 1);
-    return;
-  }
+    link_end = autolink_delim(data + start + offset + max_rewind, link_end);
 
-  link_end = autolink_delim(data, link_end);
+    if (link_end == 0) {
+      offset += max_rewind + 1;
+      continue;
+    }
 
-  if (link_end == 0) {
-    postprocess_text(parser, text, max_rewind + 1 + offset, depth + 1);
-    return;
-  }
+    cmark_node *link_node = cmark_node_new_with_mem(CMARK_NODE_LINK, parser->mem);
+    cmark_strbuf buf;
+    cmark_strbuf_init(parser->mem, &buf, 10);
+    if (auto_mailto)
+      cmark_strbuf_puts(&buf, "mailto:");
+    cmark_strbuf_put(&buf, data + start + offset + max_rewind - rewind, (bufsize_t)(link_end + rewind));
+    link_node->as.link.url = cmark_chunk_buf_detach(&buf);
+
+    cmark_node *link_text = cmark_node_new_with_mem(CMARK_NODE_TEXT, parser->mem);
+    cmark_chunk email = cmark_chunk_dup(
+      &detached_chunk,
+      start + offset + max_rewind - rewind,
+      (bufsize_t)(link_end + rewind));
+    cmark_chunk_to_cstr(parser->mem, &email);
+    link_text->as.literal = email;
+    cmark_node_append_child(link_node, link_text);
 
-  cmark_chunk_to_cstr(parser->mem, &text->as.literal);
+    cmark_node_insert_after(text, link_node);
 
-  cmark_node *link_node = cmark_node_new_with_mem(CMARK_NODE_LINK, parser->mem);
-  cmark_strbuf buf;
-  cmark_strbuf_init(parser->mem, &buf, 10);
-  if (auto_mailto)
-    cmark_strbuf_puts(&buf, "mailto:");
-  cmark_strbuf_put(&buf, data - rewind, (bufsize_t)(link_end + rewind));
-  link_node->as.link.url = cmark_chunk_buf_detach(&buf);
-
-  cmark_node *link_text = cmark_node_new_with_mem(CMARK_NODE_TEXT, parser->mem);
-  cmark_chunk email = cmark_chunk_dup(
-      &text->as.literal,
-      offset + max_rewind - rewind,
-      (bufsize_t)(link_end + rewind));
-  cmark_chunk_to_cstr(parser->mem, &email);
-  link_text->as.literal = email;
-  cmark_node_append_child(link_node, link_text);
+    cmark_node *post = cmark_node_new_with_mem(CMARK_NODE_TEXT, parser->mem);
+    post->as.literal = cmark_chunk_dup(&detached_chunk,
+                                       (bufsize_t)(start + offset + max_rewind + link_end),
+                                       (bufsize_t)(remaining - offset - max_rewind - link_end));
 
-  cmark_node_insert_after(text, link_node);
+    cmark_node_insert_after(link_node, post);
 
-  cmark_node *post = cmark_node_new_with_mem(CMARK_NODE_TEXT, parser->mem);
-  post->as.literal = cmark_chunk_dup(&text->as.literal,
-    (bufsize_t)(offset + max_rewind + link_end),
-    (bufsize_t)(size - link_end));
-  cmark_chunk_to_cstr(parser->mem, &post->as.literal);
+    text->as.literal = cmark_chunk_dup(&detached_chunk, start, offset + max_rewind - rewind);
+    cmark_chunk_to_cstr(parser->mem, &text->as.literal);
 
-  cmark_node_insert_after(link_node, post);
+    text = post;
+    start += offset + max_rewind + link_end;
+    remaining -= offset + max_rewind + link_end;
+    offset = 0;
+  }
 
-  text->as.literal.len = offset + max_rewind - rewind;
-  text->as.literal.data[text->as.literal.len] = 0;
+  // Convert the reference to allocated memory.
+  assert(!text->as.literal.alloc);
+  cmark_chunk_to_cstr(parser->mem, &text->as.literal);
 
-  postprocess_text(parser, post, 0, depth + 1);
+  // Free the detached buffer.
+  cmark_chunk_free(parser->mem, &detached_chunk);
 }
 
 static cmark_node *postprocess(cmark_syntax_extension *ext, cmark_parser *parser, cmark_node *root) {
@@ -431,7 +456,7 @@ static cmark_node *postprocess(cmark_syntax_extension *ext, cmark_parser *parser
     }
 
     if (ev == CMARK_EVENT_ENTER && node->type == CMARK_NODE_TEXT) {
-      postprocess_text(parser, node, 0, /*depth*/0);
+      postprocess_text(parser, node);
     }
   }