linux-kernel - Re: [PATCH v2] kconfig: avoid an infinite loop in oldconfig/syncconfig

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Message-ID: <CAK7LNAS8a=8n9r7kQrLTPpKwqXG1d1sd0WjJ8PQhOXHXxnSyNQ@mail.gmail.com>
Date:   Tue, 8 Aug 2023 04:25:29 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Yoann Congal <yoann.congal@...le.fr>
Cc:     linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] kconfig: avoid an infinite loop in oldconfig/syncconfig

On Sat, Aug 5, 2023 at 6:57 PM Yoann Congal <yoann.congal@...le.fr> wrote:
>
> Exit on error when asking for value that has an invalid default value
> and stdin has reached EOF. This happens in particular for hex/int
> configs without an explicit default value.
>
> Previously, this case would loop:
> * oldconfig prompts for the value but stdin has reached EOF
> * It gets the global default value : an empty string
> * This is not a valid hex/int value so it prompts again, hence the infinite loop.
>
> This case happens with a configuration like this (a hex config without a
> valid default value):
>   config TEST_KCONFIG
>        hex "Test KConfig"
>        # default 0x0
>
> And using:
>   make oldconfig < /dev/null
>
> This was discovered when working on Yocto bug[0] on a downstream
> kconfig user (U-boot)
>
> [0]: https://bugzilla.yoctoproject.org/show_bug.cgi?id=14136
>
> Signed-off-by: Yoann Congal <yoann.congal@...le.fr>
> ---
> v1->v2:
>  * Improve coding style
>  * Put more info in the commit message
>
>  scripts/kconfig/conf.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/scripts/kconfig/conf.c b/scripts/kconfig/conf.c
> index 7cf63261d951c..8f32cbbce4805 100644
> --- a/scripts/kconfig/conf.c
> +++ b/scripts/kconfig/conf.c
> @@ -377,8 +377,16 @@ static int conf_string(struct menu *menu)
>                         line[strlen(line)-1] = 0;
>                         def = line;
>                 }
> -               if (def && sym_set_string_value(sym, def))
> +               if (def && sym_set_string_value(sym, def)) {
>                         return 0;
> +               } else {
> +                       if (feof(stdin) && !sym_string_valid(sym, sym_get_string_value(sym))) {
> +                               fprintf(stderr,
> +                                       "Symbol %s has invalid default value and stdin reached EOF\n",
> +                                       sym->name);
> +                               exit(1);
> +                       }
> +               }
>         }
>  }
>
> --
> 2.30.2
>


It is strange (and consistent) to bail out
only for particular types.


I would change the code simply as follows:



--- a/scripts/kconfig/conf.c
+++ b/scripts/kconfig/conf.c
@@ -76,8 +76,10 @@ static void strip(char *str)
 /* Helper function to facilitate fgets() by Jean Sacren. */
 static void xfgets(char *str, int size, FILE *in)
 {
-       if (!fgets(str, size, in))
+       if (!fgets(str, size, in)) {
                fprintf(stderr, "\nError in reading or end of file.\n");
+               exit(1);
+       }

        if (!tty_stdio)
                printf("%s", str);






yes "" | make config

will succeed.



make config < /dev/null

will fail.





People expecting the closed stdin to succeed
may start complaining, but I believe
they must fix their wrong scripts.


-- 
Best Regards
Masahiro Yamada