Re: [musl] Bug in src/stdio/fread.c

[Rich Felker <dalias@libc.org>]

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;
> 	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 = MIN(f->rend - f->rpos, l);
> 		memcpy(dest, f->rpos, k);
> 		f->rpos += k;
> 		dest += k;
> 		l -= k;
> 	}
> 	
> 	/* Read the remainder directly */
> 	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?

Rich