Bug#609756: vsnprintf segfaults on second attempt with alloca

[Andrew Buckeridge]

Package: libc6
Version: 2.7-18lenny7

Changing to alloca malloc does not help.

/*
fprint.c - unistdio fprint function - Andrew Buckeridge
*/
#include <stdio.h>
#include <stdarg.h>
#include <unistd.h>
#include <stdlib.h>
#include "fprint.h"
/*
#include <string.h>
*/
/* +Ve == bytes written -Ve == bytes required */

int vfnprint(int fdout, int r, const char *fmt, va_list ap)
{
	int i;
	char *p;

	p=malloc(r);

	p[r-1]='\0';
/*
	memset(p,0,r);
*/
/* NB: alloca may return shit, but no it _IS_ vsnprintf */

fprintf(stderr,"\nvsnprintf(%d,%d,%p,...)=",fdout,r,fmt);

/* segfault inside this  */
	i=vsnprintf(p,r,fmt,ap);

fprintf(stderr,"=%d\n",i);

	if(i<0) {
		free(p);
		return 1-2*r;
	}
	if(i<r) {
		i=((write(fdout,p,i))==i)?i:-1;
		free(p);
		return i;
	}
	free(p);
	return -i;
}

/* +Ve == bytes written -Ve == failure */

int vfprint(int fdout, const char *fmt, va_list ap)
{
	int i=NONSTDBUF;
	i=vfnprint(fdout, i, fmt, ap);
	if(i<-1)
		i=vfnprint(fdout, 1-i, fmt, ap);
	return i;
}

int fprint(int fdout, const char *fmt, ...)
{
	va_list ap;
	int r;

	va_start(ap, fmt);
	r=vfprint(fdout, fmt, ap);
	va_end(ap);
	return r;
}