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

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Date:   Thu, 5 Oct 2023 00:47:13 +0200
From:   Yoann Congal <yoann.congal@...le.fr>
To:     Brandon Maier <brandon.maier@...lins.com>
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

On 10/4/23 23:52, Brandon Maier wrote:
> Hi Yoann,

Hi,

> 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.

Awesome! I've also found this on U-boot (but under Yocto).
I planned to get this merged here in kbuild then U-boot downstream and then Yocto.

Please CC me if you try to do something with this patch in Buildroot :)

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

Thanks!
 
> 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
>>

-- 
Yoann Congal
Smile ECS - Tech Expert