Are you an idiot or just play one or TV?
Are you an idiot or just play one or TV?
Posted Jul 23, 2009 11:15 UTC (Thu) by epa (subscriber, #39769)In reply to: Are you an idiot or just play one or TV? by khim
Parent article: Fun with NULL pointers, part 2
Why yes, I was talking about this particular case. Doing a null pointer check earlier (whether with BUG_ON(x==NULL) or some other test) would have avoided a local root exploit in this one case. That suggests that the whole approach is not completely useless, even if in other cases it doesn't help.
I am not arguing for 'defensive programming' as sometimes practised, where you cruft up the code with workarounds to silently return or do something random if a caller is buggy. That tends to hide bugs and thus cause buggier software in the long run. (Although even this kind of defensive programming can occasionally be useful, for example in safety-critical systems where the code must keep running no matter what.)
There were a lot of investigations. Number of bugs per line of code does not change too much when you switch languages, paradigms, etc.That is quite true but you cannot reason as follows: on average, more lines of code means more bugs, therefore an average 101-line program is buggier than an average 100-line program, therefore adding *this particular line of code* to *this particular* program is likely to cause a bug! Of course it depends on the individual case! Some kinds of code such as assertions (runtime checking) and type annotation (compile-time checking) exist only to catch bugs, and it doesn't make sense to say that adding them will tend to make code buggier just based on a general rule about lines of code.
An incorrect BUG_ON(x==NULL) certainly can introduce a bug into a program, but then an incorrect anything can introduce a bug.