Date: Mon, 26 Feb 2001 09:49:37 -0800 (PST) From: Matt Dillon <dillon@earth.backplane.com> To: Terry Lambert <tlambert@primenet.com> Cc: ken@kdm.org (Kenneth D. Merry), arch@FreeBSD.ORG Subject: Re: sbufs in userland Message-ID: <200102261749.f1QHnbB33892@earth.backplane.com> References: <200102261256.FAA16315@usr05.primenet.com>
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:> char *
:> safe_replacef(char **pptr, const char *ctl, ...)
:> {
:> va_list va;
:> char *optr = *pptr;
:>
:> if (ctl) {
:> va_start(va, ctl);
:> if (vasprintf(pptr, ctl, va) < 0)
:> fatalmem();
:> va_end(va);
:> }
:> safe_free(&optr);
:> return(*pptr);
:> }
:
:So basically, why is there an "if (ctl)"? Is it so you can pass
:a NULL as the second argument to turn it into a "safe_free" call?
:That's weird...
:
:
: Terry Lambert
: terry@lambert.org
Yah, that's just a left over from a NULL terminated looping construct I
wanted to support. I never wound up using the feature so I should
probably remove it.
I generally have two versions:
safe_replace(&str, original)
safe_replacef(&str, ctl, ...)
I've found that, as the syslog security hole shows us, the base version
of any string manipulation function should never be var-args or people
will start using it with arguments as the second argument instead of ctl.
I also constructed a poor-mans string-append routine, aka safe_append()
and safe_appendf(). Obviously extremely inefficient if used to build
large strings since I free/malloc or realloc on each call, but otherwise
generally quite useful. It utilizes the same idea of allowing the
initial string to be NULL. So:
char *str = NULL;
for (node = firstnode(); node; node = nextnode(node)) {
safe_appendf(&str, "%d\n", node->value);
}
...
safe_free(&str); /* str could very well be NULL if the list was empty */
All of these routines call fatalmem() (i.e. and exit) if the allocation
fails, so all users of the routines can simply assume that they succeed.
Which makes them a whole lot easier to use safely then the libc
equivalents.
-Matt
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