[PATCH 1/5] libsepol: do not dereference NULL if stack_init fails

[Nicolas Iooss]

In cond_expr_to_cil(), when stack_init() fails to allocate a stack, the
function calls stack_pop() with stack = NULL. Then stack_pop()
dereferences the pointer ("if (stack->pos == -1) {"), which is NULL.

Fix this by moving the stack cleaning loop in a "if (stack != NULL)"
block.

This issue is reported by clang's static analyzer with the following
message:

    module_to_cil.c:463:6: warning: Access to field 'pos' results in a
    dereference of a null pointer (loaded from variable 'stack')
        if (stack->pos == -1) {
            ^~~~~~~~~~

Signed-off-by: Nicolas Iooss <nicolas.io...@m4x.org>
---
 libsepol/src/module_to_cil.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/libsepol/src/module_to_cil.c b/libsepol/src/module_to_cil.c
index 5b8ed19eaa14..c6f1659c84ef 100644
--- a/libsepol/src/module_to_cil.c
+++ b/libsepol/src/module_to_cil.c
@@ -1917,10 +1917,12 @@ exit:
        free(new_val);
        free(val1);
        free(val2);
-       while ((val1 = stack_pop(stack)) != NULL) {
-               free(val1);
+       if (stack != NULL) {
+               while ((val1 = stack_pop(stack)) != NULL) {
+                       free(val1);
+               }
+               stack_destroy(&stack);
        }
-       stack_destroy(&stack);
 
        return rc;
 }
-- 
2.17.0