Would be fascinating to know how the GPL operates in this case. The way I see it, it can't be that a distributor is liable for patents they do not own on code they distribute. Otherwise the GPL becomes almost non-viable since even the mere act of distributing code under it puts you into the chain of liability. It can only be that you are granting an implicit license for patents you actually own or have the right to re-license.
In section 7, it says that distribution is banned if the distributor has patent obligations preventing the recipient from having the four freedoms
The distributor is not liable for patents they do not own, but they can loose distribution permission depending on the situation.
Same is actually true for anything GPL say. The worst case scenario is always that the distributor loose the permission to distribution, and thus become liable under copyright infringement if they distribute while violating the license.
Interesting question. Obviously the people behind the LAME MP3 encoder cannot extend you any patent rights on MP3 encoding, you would have to go to MPEG-LA for that. On the other hand, if you take that MP3 encoder and embed it in a device you start selling, you'll most certainly put yourself in the chain of liability, no?
