[Rd] model.matrix memory problem (PR#13838)

[Duncan Murdoch]

On 7/17/2009 1:15 PM, Olaf Mersmann wrote:
> Hi,
> 
> Excerpts from Torsten.Hothorn's message of Thu Jul 16 17:20:10 +0200 2009:
>> `model.matrix' might kill R with a segfault (on a illposed problem, but anyway):
>> 
>> mydf <- as.data.frame(sapply(1:40, function(i) gl(2, 100)))
>> f <- as.formula(paste("~ - 1 + ", paste(names(mydf), collapse = ":"), sep = ""))
>> X <- model.matrix(f, data = mydf)
>> 
>>   *** caught segfault ***
>> address 0x18, cause 'memory not mapped'
>> Segmentation fault
> 
> I've taken a look at this. The problem lies in lines 1784 - 1798 of
> src/main/model.c. What happens is that 'k' overflows (signed
> int). That means k is 0 after the loop an nc is set to 0. That means
> the allocated model matrix 'x' is too small which results in the
> observed segfault. 
> 
> I can provide a patch which checks for overflow and throws an error if
> that is the desired behaviour.

Thanks for tracking this down.  I'll fix it; your patch would likely be 
helpful, but your description is clear enough.

Duncan Murdoch