kconfig: Clear "written" flag to avoid data loss

commit 0c5b6c28 upstream.

Prior to this commit, starting nconfig, xconfig or gconfig, and saving
the .config file more than once caused data loss, where a .config file
that contained only comments would be written to disk starting from the
second save operation.

This bug manifests itself because the SYMBOL_WRITTEN flag is never
cleared after the first call to conf_write, and subsequent calls to
conf_write then skip all of the configuration symbols due to the
SYMBOL_WRITTEN flag being set.

This commit resolves this issue by clearing the SYMBOL_WRITTEN flag
from all symbols before conf_write returns.

Fixes: 8e2442a5 ("kconfig: fix missing choice values in auto.conf")
Cc: linux-stable <stable@vger.kernel.org> # 4.19+
Signed-off-by: M. Vefa Bicakci <m.v.b@runbox.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

scripts/kconfig/confdata.c

@@ -784,6 +784,7 @@ int conf_write(const char *name)
 	const char *str;
 	char dirname[PATH_MAX+1], tmpname[PATH_MAX+22], newname[PATH_MAX+8];
 	char *env;
+	int i;
 
 	dirname[0] = 0;
 	if (name && name[0]) {
@@ -860,6 +861,9 @@ int conf_write(const char *name)
 	}
 	fclose(out);
 
+	for_all_symbols(i, sym)
+		sym->flags &= ~SYMBOL_WRITTEN;
+
 	if (*tmpname) {
 		strcat(dirname, basename);
 		strcat(dirname, ".old");