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Fix #76813: Access_violation_near_NULL_on_source_operand #6464

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Fix #76813: Access_violation_near_NULL_on_source_operand #6464

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06ef76a
Fix #76813: Access_violation_near_NULL_on_source_operand
cmb69 Nov 27, 2020
c6e857b
Cleaner solution
cmb69 Nov 28, 2020
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5 changes: 4 additions & 1 deletion sapi/phpdbg/phpdbg_lexer.l
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Expand Up @@ -84,7 +84,10 @@ ADDR [0][x][a-fA-F0-9]+
OPCODE (ZEND_|zend_)([A-Za-z])+
INPUT ("\\"[#"']|["]("\\\\"|"\\"["]|[^\n\000"])+["]|[']("\\"[']|"\\\\"|[^\n\000'])+[']|[^\n\000#"'])+

<!*> := yyleng = (size_t) YYCURSOR - (size_t) yytext;
<!*> {
if (YYCURSOR == NULL) return T_UNEXPECTED;
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How does YYCURSOR become null?

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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.

yyleng = (size_t) YYCURSOR - (size_t) yytext;
}

<*>[\n\000] {
return 0;
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8 changes: 6 additions & 2 deletions sapi/phpdbg/phpdbg_parser.y
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Expand Up @@ -63,11 +63,15 @@ typedef void* yyscan_t;
%% /* Rules */

input
: command { $$ = $1; }
| input T_SEPARATOR command { phpdbg_stack_separate($1.top); $$ = $3; }
: non_empty_input { $$ = $1; }
| /* empty */
;

non_empty_input
: command { $$ = $1; }
| non_empty_input T_SEPARATOR command { phpdbg_stack_separate($1.top); $$ = $3; }
;

command
: parameters { $$.top = PHPDBG_G(parser_stack)->top; }
| full_expression { phpdbg_stack_push(PHPDBG_G(parser_stack), &$1); $$.top = PHPDBG_G(parser_stack)->top; }
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10 changes: 10 additions & 0 deletions sapi/phpdbg/tests/bug76813.phpt
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@@ -0,0 +1,10 @@
--TEST--
Bug #76813 (Access_violation_near_NULL_on_source_operand)
--PHPDBG--
"#!==)===\377\377\276\242="
#!==)===\377\377\276\242=
--EXPECT--
prompt> [Parse Error: syntax error, unexpected input, expecting $end]
prompt> [Parse Error: syntax error, unexpected # (pound sign), expecting $end]
prompt> [Parse Error: syntax error, unexpected # (pound sign), expecting $end]
prompt>