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Date: Sat, 10 Jul 2021 13:17:54 -0400
From: David Edelsohn <dje.gcc@...il.com>
To: musl@...ts.openwall.com
Cc: jason <jason@...omnia247.nl>
Subject: Re: Bug in src/stdio/fread.c
On Sat, Jul 10, 2021 at 1:13 PM David Edelsohn <dje.gcc@...il.com> wrote:
>
> On Sat, Jul 10, 2021 at 12:51 PM Rich Felker <dalias@...c.org> wrote:
> >
> > On Sat, Jul 10, 2021 at 03:10:26PM +0200, jason wrote:
> > > If you look at the code:
> > >
> > > size_t fread(void *restrict destv, size_t size, size_t nmemb, FILE *restrict f)
> > > {
> > > unsigned char *dest = destv;
>
> k declared but not initialized.
>
> > > size_t len = size*nmemb, l = len, k;
> > > if (!size) nmemb = 0;
> > >
> > > FLOCK(f);
> > >
> > > f->mode |= f->mode-1;
> > >
> > > if (f->rpos != f->rend) {
> > > /* First exhaust the buffer. */
>
> k set to value.
>
> > > k = MIN(f->rend - f->rpos, l);
> > > memcpy(dest, f->rpos, k);
> > > f->rpos += k;
> > > dest += k;
> > > l -= k;
> > > }
> > >
> > > /* Read the remainder directly */
>
> USE of k. If f->rpos == f->rend, k was never set before use for the
> first iteration of the loop.
>
> > > for (; l; l-=k, dest+=k) {
> > > k = __toread(f) ? 0 : f->read(f, dest, l);
> > > if (!k) {
> > > FUNLOCK(f);
> > > return (len-l)/size;
> > > }
> > > }
> > >
> > > FUNLOCK(f);
> > > return nmemb;
> > > }
> > >
> > > Consider what happens when f->rpos == f->rend: k is used uninitialized.
> >
> > At which line?
Sorry, my mistake, k will be set in the loop before the iteration
expression is evaluated.
- David
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