config: handle NULL value when parsing non-bools

When the config parser sees an "implicit" bool like:

  [core]
  someVariable

it passes NULL to the config callback. Any callback code which expects a
string must check for NULL. This usually happens via helpers like
git_config_string(), etc, but some custom code forgets to do so and will
segfault.

These are all fairly vanilla cases where the solution is just the usual
pattern of:

  if (!value)
        return config_error_nonbool(var);

though note that in a few cases we have to split initializers like:

  int some_var = initializer();

into:

  int some_var;
  if (!value)
        return config_error_nonbool(var);
  some_var = initializer();

There are still some broken instances after this patch, which I'll
address on their own in individual patches after this one.

Reported-by: Carlos Andrés Ramírez Cataño <antaigroupltda@gmail.com>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/config.c b/config.c
index b330c7adb4..18085c7e38 100644
--- a/config.c
+++ b/config.c
@@ -1386,6 +1386,8 @@ static int git_default_core_config(const char *var, const char *value,
 		return 0;
 	}
 	if (!strcmp(var, "core.checkstat")) {
+		if (!value)
+			return config_error_nonbool(var);
 		if (!strcasecmp(value, "default"))
 			check_stat = 1;
 		else if (!strcasecmp(value, "minimal"))
@@ -1547,11 +1549,15 @@ static int git_default_core_config(const char *var, const char *value,
 	}
 
 	if (!strcmp(var, "core.checkroundtripencoding")) {
+		if (!value)
+			return config_error_nonbool(var);
 		check_roundtrip_encoding = xstrdup(value);
 		return 0;
 	}
 
 	if (!strcmp(var, "core.notesref")) {
+		if (!value)
+			return config_error_nonbool(var);
 		notes_ref_name = xstrdup(value);
 		return 0;
 	}
@@ -1619,6 +1625,8 @@ static int git_default_core_config(const char *var, const char *value,
 	}
 
 	if (!strcmp(var, "core.createobject")) {
+		if (!value)
+			return config_error_nonbool(var);
 		if (!strcmp(value, "rename"))
 			object_creation_mode = OBJECT_CREATION_USES_RENAMES;
 		else if (!strcmp(value, "link"))