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autolink: avoid out-of-bounds read in validate_protocol #296

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autolink: avoid out-of-bounds read in validate_protocol #296

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9 changes: 6 additions & 3 deletions extensions/autolink.c
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Original file line number Diff line number Diff line change
Expand Up @@ -269,7 +269,7 @@ 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, uint8_t* start) {
size_t len = strlen(protocol);

// Check that the protocol matches
Expand All @@ -279,6 +279,9 @@ static bool validate_protocol(char protocol[], uint8_t *data, int rewind) {
}
}

if (start >= data - rewind - len)
return true; // start of text, skip prev_char check

char prev_char = data[-rewind - len - 1];

// Make sure the character before the protocol is non-alphanumeric
Expand Down Expand Up @@ -323,12 +326,12 @@ static void postprocess_text(cmark_parser *parser, cmark_node *text, int offset,
continue;

if (strchr(":", c) != NULL) {
if (validate_protocol("mailto:", data, rewind)) {
if (validate_protocol("mailto:", data, rewind, text->as.literal.data)) {
auto_mailto = false;
continue;
}

if (validate_protocol("xmpp:", data, rewind)) {
if (validate_protocol("xmpp:", data, rewind, text->as.literal.data)) {
auto_mailto = false;
is_xmpp = true;
continue;
Expand Down