[PATCH -next] integrity: return early if audit_log_start return NULL

[Gaosheng Cui]

audit_log_start() may return NULL in below cases:
  - when audit is not initialized.
  - when audit backlog limit exceeds.

After the call to audit_log_start() is made and then possible NULL audit
buffer argument is passed to audit_log_*() functions, audit_log_*()
functions return immediately in case of a NULL audit buffer argument.

It is not necessary for audit_log_*() functions to be called with
NULL audit buffer argument, so return early when audit_log_start()
returns NULL.

Signed-off-by: Gaosheng Cui <cuigaosheng1 at huawei.com>
---
 security/integrity/integrity_audit.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/security/integrity/integrity_audit.c b/security/integrity/integrity_audit.c
index 29220056207f..fbc032185d72 100644
--- a/security/integrity/integrity_audit.c
+++ b/security/integrity/integrity_audit.c
@@ -45,6 +45,8 @@ void integrity_audit_message(int audit_msgno, struct inode *inode,
 		return;
 
 	ab = audit_log_start(audit_context(), GFP_KERNEL, audit_msgno);
+	if (unlikely(!ab))
+		return;
 	audit_log_format(ab, "pid=%d uid=%u auid=%u ses=%u",
 			 task_pid_nr(current),
 			 from_kuid(&init_user_ns, current_uid()),
-- 
2.30.0