[PATCH] checkpolicy/fuzz: ignore invalid policy versions for the Xen target

Xen only supports specific policy versions (see policydb_compat[] in
libsepol/src/policydb.c); the fuzzer will always fail on the
policydb_write() call if given a version not listed in that array with
a .target_platform of SEPOL_TARGET_XEN.

Reported-by: oss-fuzz (issue 539336382)
Signed-off-by: Stephen Smalley <[email protected]>
---
 checkpolicy/fuzz/checkpolicy-fuzzer.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/checkpolicy/fuzz/checkpolicy-fuzzer.c b/checkpolicy/fuzz/checkpolicy-fuzzer.c
index 7db0d4c8..c58d10e9 100644
--- a/checkpolicy/fuzz/checkpolicy-fuzzer.c
+++ b/checkpolicy/fuzz/checkpolicy-fuzzer.c
@@ -159,7 +159,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
 	/*
 	 * Take the first byte whether to generate a SELinux or Xen policy,
 	 * the second byte whether to parse as MLS policy,
-	 * and the second byte as policy version.
+	 * and the third byte as policy version.
 	 */
 	if (size < 3)
 		return 0;
@@ -189,6 +189,10 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
 	if (policyvers < POLICYDB_VERSION_MIN ||
 	    policyvers > POLICYDB_VERSION_MAX)
 		return 0;
+	if (platform == SEPOL_TARGET_XEN &&
+	    policyvers != POLICYDB_VERSION_XEN_DEVICETREE &&
+	    policyvers != POLICYDB_VERSION_BOUNDARY)
+		return 0;
 	data += 3;
 	size -= 3;
 
-- 
2.55.0