I have no idea about the claim of a backdoor. But here is the source:

Matt Mackall: "It's worth noting that the maintainer of record (me) for the Linux RNG quit the project about two years ago precisely because Linus decided to include a patch from Intel to allow their unauditable RdRand to bypass the entropy pool over my strenuous objections. "

https://cryptome.wikileaks.org/2013/07/intel-bed-nsa.htm?utm...