linux-kernel - Re: [PATCH v4] kconfig: avoid an infinite loop in oldconfig/syncconfig

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Message-ID: <CAK7LNATaX5S1MwmJ4EGd7YGf3pJ0tEUABcJX6stSxHUsB0ca6w@mail.gmail.com>
Date:   Fri, 3 Nov 2023 22:53:38 +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,
        Randy Dunlap <rdunlap@...radead.org>,
        Brandon Maier <brandon.maier@...lins.com>
Subject: Re: [PATCH v4] kconfig: avoid an infinite loop in oldconfig/syncconfig

On Tue, Oct 31, 2023 at 8:17 PM Yoann Congal <yoann.congal@...le.fr> wrote:
>
> Exit on error when asking for value and reading stdin returns an error
> (mainly if it has reached EOF or is closed).
>
> This infinite loop 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>
> Tested-by: Brandon Maier <brandon.maier@...lins.com>
> ---
> v3->v4:
>  * Added Brandon Maier's "Tested-by". Thanks!
> v2->v3:
>  * Simplify the patch by fusing comments of :
>    * Masahiro Yamada : Exit as soon as reading stdin hits an error
>    * Randy Dunlap : Display the name of the currently read symbol
> v1->v2:
>  * Improve coding style
>  * Put more info in the commit message
>
>  scripts/kconfig/conf.c | 19 +++++++++++++++----
>  1 file changed, 15 insertions(+), 4 deletions(-)
>
> diff --git a/scripts/kconfig/conf.c b/scripts/kconfig/conf.c
> index 33d19e419908..68f0c649a805 100644
> --- a/scripts/kconfig/conf.c
> +++ b/scripts/kconfig/conf.c
> @@ -74,13 +74,17 @@ static void strip(char *str)
>  }
>
>  /* Helper function to facilitate fgets() by Jean Sacren. */
> -static void xfgets(char *str, int size, FILE *in)
> +static int xfgets(char *str, int size, FILE *in)
>  {
> +       int ret = 0;
> +
>         if (!fgets(str, size, in))
> -               fprintf(stderr, "\nError in reading or end of file.\n");
> +               ret = -1;
>
>         if (!tty_stdio)
>                 printf("%s", str);
> +
> +       return ret;
>  }



This is not what I suggested.


I suggested much simpler code:

https://lore.kernel.org/linux-kbuild/CAK7LNAS8a=8n9r7kQrLTPpKwqXG1d1sd0WjJ8PQhOXHXxnSyNQ@mail.gmail.com/


It is easy to know the symbol name that is causing the issue;
it was shown in the prompt just before the failure.



Also, please note that the 'x' prefix is often used
for functions that do not require error check.
(e.g. xmalloc)









>
>  static void set_randconfig_seed(void)
> @@ -339,7 +343,10 @@ static int conf_askvalue(struct symbol *sym, const char *def)
>                 /* fall through */
>         default:
>                 fflush(stdout);
> -               xfgets(line, sizeof(line), stdin);
> +               if (xfgets(line, sizeof(line), stdin) != 0) {
> +                       fprintf(stderr, "Error while reading value of symbol \"%s\"\n", sym->name);
> +                       exit(1);
> +               }
>                 break;
>         }
>
> @@ -521,7 +528,11 @@ static int conf_choice(struct menu *menu)
>                         /* fall through */
>                 case oldaskconfig:
>                         fflush(stdout);
> -                       xfgets(line, sizeof(line), stdin);
> +                       if (xfgets(line, sizeof(line), stdin) != 0) {
> +                               fprintf(stderr, "Error while reading value of symbol \"%s\"\n",
> +                                               sym->name);
> +                               exit(1);
> +                       }
>                         strip(line);
>                         if (line[0] == '?') {
>                                 print_help(menu);
> --
> 2.30.2
>


-- 
Best Regards
Masahiro Yamada