[PATCH] ash: fix parsing of alias expansion + bash features

[Denys Vlasenko]

Applied, thank you!

On Thu, May 2, 2024 at 2:14 PM Ron Yorston <rmy at pobox.com> wrote:
>
> An alias expansion immediately followed by '<' and a newline is
> parsed incorrectly:
>
>    ~ $ alias x='echo yo'
>    ~ $ x<
>    yo
>    ~ $
>    sh: syntax error: unexpected newline
>
> The echo is executed and an error is printed on the next command
> submission.  In dash the echo isn't executed and the error is
> reported immediately:
>
>    $ alias x='echo yo'
>    $ x<
>    dash: 3: Syntax error: newline unexpected
>    $
>
> The difference between BusyBox and dash is that BusyBox supports
> bash-style process substitution and output redirection.  These
> require checking for '<(', '>(' and '&>' in readtoken1().
>
> In the case above, when the end of the alias is found, the '<' and
> the following newline are both read to check for '<('.  Since
> there's no match both characters are pushed back.
>
> The next input is obtained by reading the expansion of the alias.
> Once this string is exhausted the next call to __pgetc() calls
> preadbuffer() which pops the string, reverts to the previous input
> and recursively calls __pgetc().  This request is satisified from
> the pungetc buffer.  But the first __pgetc() doesn't know this:
> it sees the character has come from preadbuffer() so it (incorrectly)
> updates the pungetc buffer.
>
> Resolve the issue by moving the code to pop the string and fetch
> the next character up from preadbuffer() into __pgetc().
>
> function                                             old     new   delta
> pgetc                                                 28     589    +561
> __pgetc                                              607       -    -607
> ------------------------------------------------------------------------------
> (add/remove: 0/1 grow/shrink: 1/0 up/down: 561/-607)          Total: -46 bytes
>
> Signed-off-by: Ron Yorston <rmy at pobox.com>
> ---
>  shell/ash.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/shell/ash.c b/shell/ash.c
> index 4ca4c6c56..5df0ba625 100644
> --- a/shell/ash.c
> +++ b/shell/ash.c
> @@ -10934,11 +10934,6 @@ preadbuffer(void)
>         char *q;
>         int more;
>
> -       if (unlikely(g_parsefile->strpush)) {
> -               popstring();
> -               return __pgetc();
> -       }
> -
>         if (g_parsefile->buf == NULL) {
>                 pgetc_debug("preadbuffer PEOF1");
>                 return PEOF;
> @@ -11053,8 +11048,13 @@ static int __pgetc(void)
>
>         if (--g_parsefile->left_in_line >= 0)
>                 c = (unsigned char)*g_parsefile->next_to_pgetc++;
> -       else
> +       else {
> +               if (unlikely(g_parsefile->strpush)) {
> +                       popstring();
> +                       return __pgetc();
> +               }
>                 c = preadbuffer();
> +       }
>
>         g_parsefile->lastc[1] = g_parsefile->lastc[0];
>         g_parsefile->lastc[0] = c;
> --
> 2.44.0
>
> _______________________________________________
> busybox mailing list
> busybox at busybox.net
> http://lists.busybox.net/mailman/listinfo/busybox