linux-kernel - Re: [PATCH v3] kconfig: avoid an infinite loop in oldconfig/syncconfig

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Message-ID: <wikmpahnfwa3bgei7mglda53l6smzieinlogvvswlwhw6l7uaw@a4qgkxqjkz4h>
Date:   Wed, 4 Oct 2023 21:52:19 +0000
From:   Brandon Maier <brandon.maier@...lins.com>
To:     Yoann Congal <yoann.congal@...le.fr>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH v3] kconfig: avoid an infinite loop in
 oldconfig/syncconfig

Hi Yoann,

We encountered the same issue in U-Boot under Buildroot. I verified that
this patch fixes the issue, causing Kconfig to exit out instead of
infinitely looping. Thanks for the fix.

Tested-by: Brandon Maier <brandon.maier@...lins.com>

On Tue, Sep 12, 2023 at 05:48:11PM +0200, Yoann Congal 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>
> ---
> 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 33d19e419908b..68f0c649a805e 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;
>  }
>
>  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
>