[PATCH] selinux: check the return value of audit_log_start()

[xkernel . wang]

From: Xiaoke Wang <xkernel.wang@xxxxxxxxxxx>

audit_log_start() returns audit_buffer pointer on success or NULL on
error. It is better to check the return value of it so to prevent
potential memory access error.

Signed-off-by: Xiaoke Wang <xkernel.wang@xxxxxxxxxxx>
---
 security/selinux/ss/services.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
index e5f1b27..759d878 100644
--- a/security/selinux/ss/services.c
+++ b/security/selinux/ss/services.c
@@ -3277,11 +3277,13 @@ int security_sid_mls_copy(struct selinux_state *state,
 				ab = audit_log_start(audit_context(),
 						     GFP_ATOMIC,
 						     AUDIT_SELINUX_ERR);
-				audit_log_format(ab,
-						 "op=security_sid_mls_copy invalid_context=");
-				/* don't record NUL with untrusted strings */
-				audit_log_n_untrustedstring(ab, s, len - 1);
-				audit_log_end(ab);
+				if (ab) {
+					audit_log_format(ab,
+							"op=security_sid_mls_copy invalid_context=");
+					/* don't record NUL with untrusted strings */
+					audit_log_n_untrustedstring(ab, s, len - 1);
+					audit_log_end(ab);
+				}
 				kfree(s);
 			}
 			goto out_unlock;
--