UDP sendto fails with EFAULT (bad address) when buf is nullptr but len is also 0

Host environment

• Operating system: Ubuntu 25.04
• OS/kernel version: 6.14.0-28-generic #28-Ubuntu SMP PREEMPT_DYNAMIC Wed Jul 23 12:05:14 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux
• Architecture: x86_64
• QEMU flavor: qemu-arm64-static
• QEMU version: qemu-aarch64 version 9.2.1 (Debian 1:9.2.1+ds-1ubuntu5)
• QEMU command line: used via binfmt

Emulated/Virtualized environment

• Operating system: Same as host
• OS/kernel version: Same as host
• Architecture: ARM64

Description of problem

For UDP sockets, sendto syscalls fail with EFAULT (bad address) when trying to specify buf = nullptr with len = 0.

No validation of / access to buf should occur when len is 0.

Steps to reproduce

1. Try to send on an UDP socket with sendto(socket, nullptr, 0, ...)

Additional information