3 ms·

What did you change it to?

by rzzzt 6y ago

muricula 6y ago
This is pure speculation, but they may have changed it to foo==false. In C a boolean is just a byte which conventionally has the values 0 or 1, but an attacker which controls a boolean can give it the value of 2, and 2!=true and 2!=false. This has lead to real exploits: https://windows-internals.com/exploiting-a-simple-vulnerability-in-35-easy-steps-or-less/ https://windows-internals.com/exploiting-a-simple-vulnerabil... When writing C or C++, never compare against true.
- HeyLaughingBoy 6y ago
  I'm not sure that's right. Too lazy to look it up right now, but my recollection is that in C, 0 is False and anything else is True.
  - stonemetal12 6y ago
    if 47 evaluates the true branch. So in that sense you are correct, however standard C99 (the above mentioned bug uses win32's TRUE which is defined the same way) does #define true 1 therefore 47==true is false, even if 47 is true when evaluated. int a = 47; if a is true if a == true is false if a == false is false int b; b = a == true; b = 0 b = a != true; b = 1 b = a == false; b = 0 b = a != false; b = 1
  - closeparen 6y ago
    Nonzero values are truthy. You can use them bare in predicates. But they are not "== true."
serial_dev 6y ago
I'd guess if(!foo). It makes sense in some languages where the value can only be either true or false. It will lead to nasty bugs if the value can be null, or the language has truthy-falsy values and the condition accepts non bool values
- rzzzt 6y ago
  You and muricula's sibling comment is the reason I asked :) Occasionally it is hard to spot the "!" between "if" and "(", and having to figure out if it is an omission or it was deliberate. I was wondering if spelling it out as "foo == false" is worthwhile.
  - HeyLaughingBoy 6y ago
    At one job I had, our programming standards dictated that we would have to write "if (false == foo)" to account for the case where someone accidentally types = instead of ==
    - zentiggr 6y ago
      That's not rare, anyway... unless the linter can flag == <bool>, and suggest fixes.
    - MauranKilom 6y ago
      Commonly called "Yoda conditions": https://en.wikipedia.org/wiki/Yoda_conditions https://en.wikipedia.org/wiki/Yoda_conditions

What did you change it to?

by rzzzt 6y ago

What did you change it to?

This is pure speculation, but they may have changed it to foo==false. In C a boolean is just a byte which conventionally has the values 0 or 1, but an attacker which controls a boolean can give it the value of 2, and 2!=true and 2!=false. This has lead to real exploits: https://windows-internals.com/exploiting-a-simple-vulnerability-in-35-easy-steps-or-less/ https://windows-internals.com/exploiting-a-simple-vulnerabil... When writing C or C++, never compare against true.

HeyLaughingBoy 6y ago
I'm not sure that's right. Too lazy to look it up right now, but my recollection is that in C, 0 is False and anything else is True.
- stonemetal12 6y ago
  if 47 evaluates the true branch. So in that sense you are correct, however standard C99 (the above mentioned bug uses win32's TRUE which is defined the same way) does #define true 1 therefore 47==true is false, even if 47 is true when evaluated. int a = 47; if a is true if a == true is false if a == false is false int b; b = a == true; b = 0 b = a != true; b = 1 b = a == false; b = 0 b = a != false; b = 1
- closeparen 6y ago
  Nonzero values are truthy. You can use them bare in predicates. But they are not "== true."

serial_dev 6y ago

I'd guess if(!foo). It makes sense in some languages where the value can only be either true or false. It will lead to nasty bugs if the value can be null, or the language has truthy-falsy values and the condition accepts non bool values

rzzzt 6y ago
You and muricula's sibling comment is the reason I asked :) Occasionally it is hard to spot the "!" between "if" and "(", and having to figure out if it is an omission or it was deliberate. I was wondering if spelling it out as "foo == false" is worthwhile.
- HeyLaughingBoy 6y ago
  At one job I had, our programming standards dictated that we would have to write "if (false == foo)" to account for the case where someone accidentally types = instead of ==
  - zentiggr 6y ago
    That's not rare, anyway... unless the linter can flag == <bool>, and suggest fixes.
  - MauranKilom 6y ago
    Commonly called "Yoda conditions": https://en.wikipedia.org/wiki/Yoda_conditions https://en.wikipedia.org/wiki/Yoda_conditions