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

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Date:   Tue, 31 Oct 2023 12:16:47 +0100
From:   Yoann Congal <yoann.congal@...le.fr>
To:     Masahiro Yamada <masahiroy@...nel.org>,
        linux-kbuild@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Randy Dunlap <rdunlap@...radead.org>,
        Yoann Congal <yoann.congal@...le.fr>,
        Brandon Maier <brandon.maier@...lins.com>
Subject: [PATCH v4] kconfig: avoid an infinite loop in oldconfig/syncconfig

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;
 }
 
 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