CVE-2026-64124: net: devmem: reject dma-buf bind with non-page-aligned size or SG length

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

net: devmem: reject dma-buf bind with non-page-aligned size or SG length

netdevmembinddmabuf() trusts dmabuf->size and sgdmalen() to be PAGESIZE multiples without checking:

- txvec is sized dmabuf->size / PAGESIZE, and netdevmemgetniovat() only bounds-checks virtaddr < dmabuf->size before indexing txvec[virtaddr / PAGESIZE]. With size = NPAGESIZE + r (1 <= r < PAGESIZE), sendmsg() at iovbase = NPAGESIZE passes the bound check and reads txvec[N] -- one past.

- owner->area.numniovs = len / PAGESIZE while genpooladdowner() covers the full byte len, so a non-page-multiple non-final sg desyncs numniovs from the genpool region for every later sg, on both RX and TX.

dma-buf does not require page-aligned sizes, so the bind path has to enforce what its own indexing assumes. Reject both with -EINVAL.

The size check is TX-only (only txvec is sized off dmabuf->size); the SG-length check covers both directions.