userdiff: fix leaking memory for configured diff drivers

The userdiff structures may be initialized either statically on the
stack or dynamically via configuration keys. In the latter case we end
up leaking memory because we didn't have any infrastructure to discern
those strings which have been allocated statically and those which have
been allocated dynamically.

Refactor the code such that we have two pointers for each of these
strings: one that holds the value as accessed by other subsystems, and
one that points to the same string in case it has been allocated. Like
this, we can safely free the second pointer and thus plug those memory
leaks.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 29 insertions, 9 deletions

diff --git a/userdiff.c b/userdiff.c
index c4ebb9ff73..989629149f 100644
--- a/userdiff.c
+++ b/userdiff.c
@@ -399,8 +399,11 @@ static struct userdiff_driver *userdiff_find_by_namelen(const char *name, size_t
 static int parse_funcname(struct userdiff_funcname *f, const char *k,
 		const char *v, int cflags)
 {
-	if (git_config_string((char **) &f->pattern, k, v) < 0)
+	f->pattern = NULL;
+	FREE_AND_NULL(f->pattern_owned);
+	if (git_config_string(&f->pattern_owned, k, v) < 0)
 		return -1;
+	f->pattern = f->pattern_owned;
 	f->cflags = cflags;
 	return 0;
 }
@@ -444,20 +447,37 @@ int userdiff_config(const char *k, const char *v)
 		return parse_funcname(&drv->funcname, k, v, REG_EXTENDED);
 	if (!strcmp(type, "binary"))
 		return parse_tristate(&drv->binary, k, v);
-	if (!strcmp(type, "command"))
-		return git_config_string((char **) &drv->external.cmd, k, v);
+	if (!strcmp(type, "command")) {
+		FREE_AND_NULL(drv->external.cmd);
+		return git_config_string(&drv->external.cmd, k, v);
+	}
 	if (!strcmp(type, "trustexitcode")) {
 		drv->external.trust_exit_code = git_config_bool(k, v);
 		return 0;
 	}
-	if (!strcmp(type, "textconv"))
-		return git_config_string((char **) &drv->textconv, k, v);
+	if (!strcmp(type, "textconv")) {
+		int ret;
+		FREE_AND_NULL(drv->textconv_owned);
+		ret = git_config_string(&drv->textconv_owned, k, v);
+		drv->textconv = drv->textconv_owned;
+		return ret;
+	}
 	if (!strcmp(type, "cachetextconv"))
 		return parse_bool(&drv->textconv_want_cache, k, v);
-	if (!strcmp(type, "wordregex"))
-		return git_config_string((char **) &drv->word_regex, k, v);
-	if (!strcmp(type, "algorithm"))
-		return git_config_string((char **) &drv->algorithm, k, v);
+	if (!strcmp(type, "wordregex")) {
+		int ret;
+		FREE_AND_NULL(drv->word_regex_owned);
+		ret = git_config_string(&drv->word_regex_owned, k, v);
+		drv->word_regex = drv->word_regex_owned;
+		return ret;
+	}
+	if (!strcmp(type, "algorithm")) {
+		int ret;
+		FREE_AND_NULL(drv->algorithm_owned);
+		ret = git_config_string(&drv->algorithm_owned, k, v);
+		drv->algorithm = drv->algorithm_owned;
+		return ret;
+	}
 
 	return 0;
 }