Re: C's trikery semantic opens up backdoor in new Linux kernel

[Vinzent 'Gadget' Hoefler <ada.rocks@jlfencey.com>]

Duncan Sands wrote:

>> The interesting line in question is this one:
>> |if ((options == (__WCLONE|__WALL)) && (current->uid = 0))
>>
>> First this looks like a sanity check. But look closer. This single
>> line serves one single purpose: to give you root-privileges when you
>> just pass the right flags. Note the "current->uid = 0" instead of
>> "current->uid == 0". Who the hell had the fucking bad idea that
>> assignments could return values?
>
>IMHO the real problem is that

the syntax of C allows such things. Simple as that, it doesn't matter
if you even can set strict coding standards to make such things hardly
possible.

>uid is not an opaque type and can
>be changed with a simple assignment.  Much better if that required
>a function call.

You can almost always find a workaround. The problem is to use it
everytime and force people to use it.

For instance considering the simple rule that in a comparison with a
constant value you should always state the constant first:

|if ((__WCLONE|__WALL) == options) && (0 = current->uid))

wouldn't compile, either.


Vinzent.