audit: link integrity evm_write_xattrs record to syscall event

In commit fa516b66 ("EVM: Allow runtime modification of the set of
verified xattrs"), the call to audit_log_start() is missing a context to
link it to an audit event. Since this event is in user context, add
the process' syscall context to the record.

In addition, the orphaned keyword "locked" appears in the record.
Normalize this by changing it to logging the locking string "." as any
other user input in the "xattr=" field.

Please see the github issue
https://github.com/linux-audit/audit-kernel/issues/109



Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
Acked-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

security/integrity/evm/evm_secfs.c

@@ -192,7 +192,8 @@ static ssize_t evm_write_xattrs(struct file *file, const char __user *buf,
 	if (count > XATTR_NAME_MAX)
 		return -E2BIG;
 
-	ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_INTEGRITY_EVM_XATTR);
+	ab = audit_log_start(audit_context(), GFP_KERNEL,
+			     AUDIT_INTEGRITY_EVM_XATTR);
 	if (!ab)
 		return -ENOMEM;
 
@@ -214,6 +215,9 @@ static ssize_t evm_write_xattrs(struct file *file, const char __user *buf,
 	if (len && xattr->name[len-1] == '\n')
 		xattr->name[len-1] = '\0';
 
+	audit_log_format(ab, "xattr=");
+	audit_log_untrustedstring(ab, xattr->name);
+
 	if (strcmp(xattr->name, ".") == 0) {
 		evm_xattrs_locked = 1;
 		newattrs.ia_mode = S_IFREG | 0440;
@@ -222,15 +226,11 @@ static ssize_t evm_write_xattrs(struct file *file, const char __user *buf,
 		inode_lock(inode);
 		err = simple_setattr(evm_xattrs, &newattrs);
 		inode_unlock(inode);
-		audit_log_format(ab, "locked");
 		if (!err)
 			err = count;
 		goto out;
 	}
 
-	audit_log_format(ab, "xattr=");
-	audit_log_untrustedstring(ab, xattr->name);
-
 	if (strncmp(xattr->name, XATTR_SECURITY_PREFIX,
 		    XATTR_SECURITY_PREFIX_LEN) != 0) {
 		err = -EINVAL;