CVE-2026-64134: Undefined Security Weakness

In the Linux kernel, the following vulnerability has been resolved:

ALSA: pcm: Don't setup bogus iov_iter for silencing

At transition to the iov_iter for PCM data transfer, we blindly applied the iov_iter setup also for silencing (i.e. data = NULL), and it leads to a calculation of bogus iov_iter. Fortunately this didn't cause troubles on most of architectures but it goes wrong on RISC-V now, causing a NULL dereference.

Handle the NULL data case to treat the silencing in interleaved_copy() for addressing the bug above. noninterleaved_copy() has already the NULL data handling, so it doesn't need changes.