Fix #76813: Access_violation_near_NULL_on_source_operand #6464
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If no valid token has been recognized, we return `T_UNEXPECTED` instead of proceeding with an invalid scanner state. We also fix the only superficially related issue regarding empty input followed by `T_SEPARATOR` and command, which caused another segfault.
nikic
reviewed
Nov 27, 2020
sapi/phpdbg/phpdbg_lexer.l
Outdated
| @@ -84,7 +84,10 @@ ADDR [0][x][a-fA-F0-9]+ | |||
| OPCODE (ZEND_|zend_)([A-Za-z])+ | |||
| INPUT ("\\"[#"']|["]("\\\\"|"\\"["]|[^\n\000"])+["]|[']("\\"[']|"\\\\"|[^\n\000'])+[']|[^\n\000#"'])+ | |||
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| <!*> := yyleng = (size_t) YYCURSOR - (size_t) yytext; | |||
| <!*> { | |||
| if (YYCURSOR == NULL) return T_UNEXPECTED; | |||
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Condider the following input: "a\b". When backtracking, re2c sets YYCURSOR to YYMARKER, which is NULL. The re2c documentation says it would not be necessary to initialize YYMARKER, but when I do it nonetheless, there is no NULL issue here anymore, but for some reason the lexer enters the <NORMAL>{GENERIC_ID} rule, albeit with an empty text (yyleng == 0) what causes issues in unescape_string(). I don't understand why that rule is executed, since GENERIC_ID is not supposed to be empty. Anyway, if I add a suitable default rule <NORMAL>* {return T_UNEXPECTED;}, I get the desired parse error.
We avoid `YYCURSOR` becoming `NULL` by initializing `YYMARKER`, and add a default rule for `<NORMAL>` where we catch unexpected input.
nikic
approved these changes
Nov 30, 2020
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If no valid token has been recognized, we return
T_UNEXPECTEDinsteadof proceeding with an invalid scanner state.
We also fix the only superficially related issue regarding empty input
followed by
T_SEPARATORand command, which caused another segfault.