Edit report at https://bugs.php.net/bug.php?id=81368&edit=1
ID: 81368
Updated by: nikic@php.net
Reported by: yguoaz at gmail dot com
Summary: Possible divide by zero bug in zend_inference.c
-Status: Open
+Status: Feedback
Type: Bug
Package: *General Issues
Operating System: Linux
PHP Version: master-Git-2021-08-17 (Git)
Block user comment: N
Private report: N
New Comment:
op2_min <= op2_max is a general precondition. In additional, the check enforces !(op2_min <= 0
&& op2_max >= 0), or equivalently op2_min > 0 || op2_max < 0.
If op2_min > 0 then also op2_max >= op2_min > 0. If op2_max < 0 then also op2_min <=
op2_max < 0.
As such, neither op2_min or op2_max can be zero. Does that sound right?
Previous Comments:
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[2021-08-17 13:00:36] yguoaz at gmail dot com
I think the op2_min/op2_max check before is not sufficient.
For example, op2_min==0 && op2_max < 0 can bypass it.
Can this happen? This issue is found by inspection. Thus I do not have a test case here.
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[2021-08-17 12:39:34] nikic@php.net
Doesn't the op2_min/op2_max check before that exclude the possibility of a division by zero?
Can you share an example that would trigger a division by zero in this code?
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[2021-08-17 11:48:11] yguoaz at gmail dot com
Description:
------------
In the file Zend/Optimizer/zend_inference.c, the function zend_inference_calc_binary_op_range has
the following code:
case ZEND_DIV:
if (OP1_HAS_RANGE() && OP2_HAS_RANGE()) {
op1_min = OP1_MIN_RANGE();
op2_min = OP2_MIN_RANGE();
op1_max = OP1_MAX_RANGE();
op2_max = OP2_MAX_RANGE();
if (op2_min <= 0 && op2_max >= 0) {
break;
}
float_div(op1_min, op2_min, &t1, &t1_);
float_div(op1_min, op2_max, &t2, &t2_);
float_div(op1_max, op2_min, &t3, &t3_);
float_div(op1_max, op2_max, &t4, &t4_);
The function float_div uses its second argument as a divisor. If only one of
the variables from op2_min and op2_max is zero, the checking can be bypassed
and will lead to a divide by zero problem.
Here is the link to the related code in github:
https://github.com/php/php-src/blob/be2df43b08cf13b9a5791ff5eb827a125115ef52/Zend/Optimizer/zend_inference.c#L674
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Edit this bug report at https://bugs.php.net/bug.php?id=81368&edit=1