[PATCH v3 2/2] ash: catch error in arithmetic expansion in PS1

[Denys Vlasenko]

Applied, thanks!

On Thu, Apr 18, 2019 at 2:16 PM Ron Yorston <rmy at pobox.com> wrote:
>
> Setting PS1 to:
>
>    PS1='$((123+))'
>
> causes the shell to enter an infinite error loop:
>
>    sh: arithmetic syntax error
>
> Catch any exception raised by expandarg() in expandstr() and allow
> processing to continue.
>
> If either readtoken1() or expandarg() fails return an empty string.
>
> function                                             old     new   delta
> expandstr                                            262     387    +125
> ------------------------------------------------------------------------------
> (add/remove: 0/0 grow/shrink: 1/0 up/down: 125/0)             Total: 125 bytes
>
> v2: If readtoken1() fails don't try expandarg().  If either fails return
>     an empty string rather than part-digested nonsense.
> v3: Ensure there's space for the empty string on the stack.
>
> Signed-off-by: Ron Yorston <rmy at pobox.com>
> ---
>  shell/ash.c | 48 ++++++++++++++++++++++++++++++++++--------------
>  1 file changed, 34 insertions(+), 14 deletions(-)
>
> diff --git a/shell/ash.c b/shell/ash.c
> index 039524010..9bea4cd42 100644
> --- a/shell/ash.c
> +++ b/shell/ash.c
> @@ -13043,6 +13043,10 @@ expandstr(const char *ps, int syntax_type)
>         union node n;
>         int saveprompt;
>         struct parsefile *file_stop = g_parsefile;
> +       volatile int saveint;
> +       struct jmploc *volatile savehandler = exception_handler;
> +       struct jmploc jmploc;
> +       int err;
>
>         /* XXX Fix (char *) cast. */
>         setinputstring((char *)ps);
> @@ -13054,29 +13058,45 @@ expandstr(const char *ps, int syntax_type)
>          * Try a prompt with syntactically wrong command:
>          * PS1='$(date "+%H:%M:%S) > '
>          */
> -       {
> -               volatile int saveint;
> -               struct jmploc *volatile savehandler = exception_handler;
> -               struct jmploc jmploc;
> +       SAVE_INT(saveint);
> +       err = setjmp(jmploc.loc);
> +       if (err == 0) {
> +               exception_handler = &jmploc;
> +               readtoken1(pgetc(), syntax_type, FAKEEOFMARK, 0);
> +       }
> +       exception_handler = savehandler;
> +       RESTORE_INT(saveint);
> +
> +       doprompt = saveprompt;
> +
> +       unwindfiles(file_stop);
> +
> +       if (err == 0) {
> +               n.narg.type = NARG;
> +               n.narg.next = NULL;
> +               n.narg.text = wordtext;
> +               n.narg.backquote = backquotelist;
> +
> +               /* expandarg() might fail too:
> +                * PS1='$((123+))'
> +                */
>                 SAVE_INT(saveint);
> -               if (setjmp(jmploc.loc) == 0) {
> +               err = setjmp(jmploc.loc);
> +               if (err == 0) {
>                         exception_handler = &jmploc;
> -                       readtoken1(pgetc(), syntax_type, FAKEEOFMARK, 0);
> +                       expandarg(&n, NULL, EXP_QUOTED);
>                 }
>                 exception_handler = savehandler;
>                 RESTORE_INT(saveint);
>         }
>
> -       doprompt = saveprompt;
> +       if (err) {
> +               char *out;
>
> -       unwindfiles(file_stop);
> -
> -       n.narg.type = NARG;
> -       n.narg.next = NULL;
> -       n.narg.text = wordtext;
> -       n.narg.backquote = backquotelist;
> +               STARTSTACKSTR(out);
> +               STACKSTRNUL(out);
> +       }
>
> -       expandarg(&n, NULL, EXP_QUOTED);
>         return stackblock();
>  }
>
> --
> 2.20.1
>
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