[PATCH 11/15] checkpolicy: fix use-after-free on invalid sens alias

["Christian Göttsche" <cgzones@googlemail.com>]

During compilation sensitivity aliases share the level with their prime
sensitivity, until after the level has been fully defined they are
deduplicated.  If an error happens by that time the cleanup will free
the shared level multiple times, leading to a use-after-free.

Make use of the added new member of the struct level_datum.

Example policy:

    class c sid e class c{i}sensitivity S alias L;

Signed-off-by: Christian Göttsche <cgzones@googlemail.com>
---
 checkpolicy/fuzz/checkpolicy-fuzzer.c | 7 +++++++
 checkpolicy/policy_define.c           | 3 +++
 2 files changed, 10 insertions(+)

diff --git a/checkpolicy/fuzz/checkpolicy-fuzzer.c b/checkpolicy/fuzz/checkpolicy-fuzzer.c
index 0d749a02..d0221f3f 100644
--- a/checkpolicy/fuzz/checkpolicy-fuzzer.c
+++ b/checkpolicy/fuzz/checkpolicy-fuzzer.c
@@ -134,6 +134,13 @@ static int check_level(hashtab_key_t key, hashtab_datum_t datum, void *arg __att
 {
 	const level_datum_t *levdatum = (level_datum_t *) datum;
 
+	if (levdatum->copy) {
+		fprintf(stderr,
+			"Error:  sensitivity %s is still a copy!\n",
+			key);
+		abort();
+	}
+
 	// TODO: drop member defined if proven to be always set
 	if (!levdatum->isalias && !levdatum->defined) {
 		fprintf(stderr,
diff --git a/checkpolicy/policy_define.c b/checkpolicy/policy_define.c
index 44236797..360cff68 100644
--- a/checkpolicy/policy_define.c
+++ b/checkpolicy/policy_define.c
@@ -756,6 +756,7 @@ int define_sens(void)
 	}
 	level_datum_init(datum);
 	datum->isalias = FALSE;
+	datum->copy = FALSE;
 	datum->level = level;
 
 	ret = declare_symbol(SYM_LEVELS, id, datum, &value, &value);
@@ -795,6 +796,7 @@ int define_sens(void)
 		}
 		level_datum_init(aliasdatum);
 		aliasdatum->isalias = TRUE;
+		aliasdatum->copy = TRUE;
 		aliasdatum->level = level;
 
 		ret = declare_symbol(SYM_LEVELS, id, aliasdatum, NULL, &value);
@@ -1035,6 +1037,7 @@ static int clone_level(hashtab_key_t key __attribute__ ((unused)), hashtab_datum
 			return -1;
 		}
 		levdatum->level = newlevel;
+		levdatum->copy = FALSE;
 	}
 	return 0;
 }
-- 
2.43.0