Re: [PATCH][BZ #14771] Fortify tweak for snprintf et al.

[Florian Weimer <fweimer at redhat dot com>]

On 10/21/2013 01:58 PM, Joseph S. Myers wrote:
> On Mon, 21 Oct 2013, Florian Weimer wrote:
>
> > Hmm.  There is no up-front check to return EOVERFLOW in glibc, and the GCC
> > folder doesn't know about it, either. :-(  EOVERFLOW is apparently returned
> > only if the actually produced string is at least INT_MAX characters long (this
> > is the fprintf etc. behavior).
>
> Apart from the Austin Group response not really engaging with the conflict
> with a case that's fully defined in C99, I don't think there's anything
> useful for GCC to know about regarding overflows on printf folding - GCC
> can't handle strings longer than host INT_MAX (which in practice will be
> the same as target INT_MAX for glibc targets) as it uses "int" to record
> the length of a STRING_CST (in general, there are many places in GCC using
> "int" to store sizes of target objects, host allocations, etc.).

It ignores the buffer length argument to snprintf during some parts of 
folding.  This means that simple test cases for EOVERFLOW checking do 
not actually exercise the glibc implementation.  Beyond that, it's 
probably not an issue.

--
Florian Weimer / Red Hat Product Security Team