From: Stefan Sperling <stsp@stsp.name>
Subject: Re: [PATCH] fix getdelim() EOF behavior
To: enh <enh@google.com>
Cc: OpenBSD Tech <tech@openbsd.org>
Date: Fri, 10 Oct 2025 11:14:58 +0200

On Thu, Oct 09, 2025 at 04:25:21PM -0400, enh wrote:
> corresponds to glibc bug
> https://sourceware.org/bugzilla/show_bug.cgi?id=28038...
> 
> basically just "make sure you've terminated the buffer _before_ returning".

I recall seeing getline() return a non-terminated string at some point.
But at the time I couldn't reproduce this issue and then forgot about it.

This diff explains what I saw, because getline() is implemented as

	return getdelim(buf, buflen, '\n', fp);

ok stsp@ if someone else wants to commit this.


> diff --git a/lib/libc/stdio/getdelim.c b/lib/libc/stdio/getdelim.c
> index d709a3d18e1..292920e79c9 100644
> --- a/lib/libc/stdio/getdelim.c
> +++ b/lib/libc/stdio/getdelim.c
> @@ -119,13 +119,11 @@ getdelim(char **__restrict buf, size_t *__restrict buflen,
> 
>         FUNLOCKFILE(fp);
> 
> -       /* POSIX demands we return -1 on EOF. */
> -       if (off == 0)
> -               return -1;
> -
>         if (*buf != NULL)
>                 *(*buf + off) = '\0';
> -       return off;
> +
> +       /* POSIX demands we return -1 on EOF. */
> +       return (off == 0) ? -1 : off;
> 
>  error:
>         fp->_flags |= __SERR;
> 
>