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Limit the depth of nested lists #475

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Limit the depth of nested lists #475

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14 changes: 12 additions & 2 deletions src/blocks.c
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Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,14 @@
#define CODE_INDENT 4
#define TAB_STOP 4

/**
* Very deeply nested lists can cause quadratic performance issues.
* This constant is used in open_new_blocks() to limit the nesting
* depth. It is unlikely that a non-contrived markdown document will
* be nested this deeply.
*/
#define MAX_LIST_DEPTH 100

#ifndef MIN
#define MIN(x, y) ((x < y) ? x : y)
#endif
Expand Down Expand Up @@ -954,10 +962,11 @@ static void open_new_blocks(cmark_parser *parser, cmark_node **container,
bool has_content;
int save_offset;
int save_column;
size_t depth = 0;

while (cont_type != CMARK_NODE_CODE_BLOCK &&
cont_type != CMARK_NODE_HTML_BLOCK) {

depth++;
S_find_first_nonspace(parser, input);
indented = parser->indent >= CODE_INDENT;

Expand Down Expand Up @@ -1044,7 +1053,8 @@ static void open_new_blocks(cmark_parser *parser, cmark_node **container,
parser->first_nonspace + 1);
S_advance_offset(parser, input, input->len - 1 - parser->offset, false);
} else if ((!indented || cont_type == CMARK_NODE_LIST) &&
parser->indent < 4 &&
parser->indent < 4 &&
depth < MAX_LIST_DEPTH &&
(matched = parse_list_marker(
parser->mem, input, parser->first_nonspace,
(*container)->type == CMARK_NODE_PARAGRAPH, &data))) {
Expand Down