Date: Thu, 26 Sep 2002 02:16:17 -0400 From: Barney Wolff <barney@tp.databus.com> To: stable@freebsd.org Subject: Re: [v]asprintf leaks memory Message-ID: <20020926061617.GA16599@tp.databus.com> In-Reply-To: <20020925155222.GA4874@tp.databus.com> References: <20020925133219.GA59210@HAL9000.homeunix.com> <20020925155222.GA4874@tp.databus.com>
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There is possibly a more serious bug here. If vfprintf returns with
f._bf._base NULL, it would seem that *f._p = '\0'; will store
into freed memory. Perhaps harmless, but that assumes a particular
malloc implementation. What's more, if the reallocf actually switches
buffers, the 0 may not have been copied, and may have been beyond the end of
the original buffer. If vfprintf always leaves room for the 0, the
reallocf call is never necessary. I think safer code would read:
ret = vfprintf(&f, fmt, ap);
va_end(ap);
if (f._bf._base != NULL) f._bf._base = reallocf(f._bf._base, ret + 1);
if (f._bf._base != NULL) f._bf._base[ret] = '\0';
else {
errno = ENOMEM;
ret = -1;
}
*str = (char *)f._bf._base;
return ret;
}
Barney
On Wed, Sep 25, 2002 at 06:32:19AM -0700, David Schultz wrote:
> Index: src/lib/libc/stdio/asprintf.c
> ===================================================================
> RCS file: /home/ncvs/src/lib/libc/stdio/asprintf.c,v
> retrieving revision 1.6
> diff -u -u -r1.6 asprintf.c
> --- src/lib/libc/stdio/asprintf.c 1999/08/28 00:00:55 1.6
> +++ src/lib/libc/stdio/asprintf.c 2002/09/25 13:08:48
> @@ -71,7 +71,8 @@
> ret = vfprintf(&f, fmt, ap);
> *f._p = '\0';
> va_end(ap);
> - f._bf._base = reallocf(f._bf._base, f._bf._size + 1);
> + if (f._bf._base != NULL)
> + f._bf._base = reallocf(f._bf._base, f._bf._size + 1);
> if (f._bf._base == NULL) {
> errno = ENOMEM;
> ret = -1;
--
Barney Wolff
I'm available by contract or FT: http://www.databus.com/bwresume.pdf
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