Re: Secure coding in C (was Re: Administrivia #4883)

[mikael.olsson () ENTERNET SE (Mikael Olsson)]

Blue Boar wrote:
> So, the test above was to take a 10 character buffer, and try to
> use snprintf to cram something longer in it.  If snprintf was
> broken like the man page suggested, then the 10th character
> would have been the letter l from "really", instead of a zero
> as it should be.  However, it works just fine, and the 10th
> character is a 0.
>
> And that's the right thing.. it just means the documentation needs
> an update. :)

It also means that someone is going to assume that they can use
snprintf() without any precautions, since
"their code will only ever run on solaris" until someone
decides to port it, and forgets about fixing the snprintf()
SNAFUs.

Myself, I always end all my string ops by NULing the last
character in the buffer. That way I _KNOW_ I'm safe.

char mybuf[10];
strncpy(mybuf, unknowninputstring, sizeof(mybuf));
mybuf[sizeof(mybuf)-1]='\0';

Oh, and by the way, these few lines placed in a commonly
included help file help a long way:
#define strcpy __do_NOT_use_strcpy__
#define sprintf __do_NOT_use_sprintf__
etc etc etc ...

All's well :-)

/Mike

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