xsk: avoid store-tearing when assigning umem

xsk: avoid store-tearing when assigning umem

[ Upstream commit 9764f4b301c3e7eb3b75eec85b73cad449cdbb0d ]

The umem member of struct xdp_sock is read outside of the control
mutex, in the mmap implementation, and needs a WRITE_ONCE to avoid
potential store-tearing.

Acked-by: Jonathan Lemon <jonathan.lemon@gmail.com>
Fixes: 423f38329d26 ("xsk: add umem fill queue support and mmap")
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>