[PATCH 2/3] libsepol: cil: show an error when cil_expr_to_string() fails

[Nicolas Iooss <nicolas.iooss@xxxxxxx>]

cil_tree_print_expr() calls cil_expr_to_string() in order to compute a
string expression into expr_str. If this function fails, expr_str is
left unitialized but its value is dereferenced with:

    cil_log(CIL_INFO, "%s)", expr_str);

Prevent such an issue by checking cil_expr_to_string()'s return value
before using expr_str.

This issue has been found with clang's static analyzer.

Signed-off-by: Nicolas Iooss <nicolas.iooss@xxxxxxx>
---
 libsepol/cil/src/cil_tree.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/libsepol/cil/src/cil_tree.c b/libsepol/cil/src/cil_tree.c
index d36401b41dba..b394a9d849df 100644
--- a/libsepol/cil/src/cil_tree.c
+++ b/libsepol/cil/src/cil_tree.c
@@ -503,15 +503,19 @@ exit:
 void cil_tree_print_expr(struct cil_list *datum_expr, struct cil_list *str_expr)
 {
 	char *expr_str;
+	int rc;
 
 	cil_log(CIL_INFO, "(");
 
 	if (datum_expr != NULL) {
-		cil_expr_to_string(datum_expr, &expr_str);
+		rc = cil_expr_to_string(datum_expr, &expr_str);
 	} else {
-		cil_expr_to_string(str_expr, &expr_str);
+		rc = cil_expr_to_string(str_expr, &expr_str);
+	}
+	if (rc < 0) {
+		cil_log(CIL_INFO, "ERROR)");
+		return;
 	}
-
 	cil_log(CIL_INFO, "%s)", expr_str);
 	free(expr_str);
 }
-- 
2.16.0