EVM: fix return value check in evm_write_xattrs()

In case of error, the function audit_log_start() returns NULL pointer
not ERR_PTR(). The IS_ERR() test in the return value check should be
replaced with NULL test.

Fixes: fa516b66a1bf ("EVM: Allow runtime modification of the set of verified xattrs")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Acked-by: Serge Hallyn <serge@hallyn.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

security/integrity/evm/evm_secfs.c

@@ -193,8 +193,8 @@ static ssize_t evm_write_xattrs(struct file *file, const char __user *buf,
 		return -E2BIG;
 
 	ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_INTEGRITY_EVM_XATTR);
-	if (IS_ERR(ab))
-		return PTR_ERR(ab);
+	if (!ab)
+		return -ENOMEM;
 
 	xattr = kmalloc(sizeof(struct xattr_list), GFP_KERNEL);
 	if (!xattr) {