AWS Lambda announces support for lambda:SourceFunctionArn. A new IAM condition key that can be used for IAM policy conditions that specify the ARN of the function from which a request is made. Starting today, when a function is invoked, Lambda will automatically add the new lambda:SourceFunctionArn condition key to the request context of all AWS API calls made by function code. You can use the Condition element in your IAM policy to compare the lambda:SourceFunctionArn condition key in the request context with values that you specify in your policy.
Source:: Amazon AWS