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

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

net_devmem_bind_dmabuf() trusts dmabuf->size and sg_dma_len() to be
PAGE_SIZE multiples without checking:

  - tx_vec is sized dmabuf->size / PAGE_SIZE, and
    net_devmem_get_niov_at() only bounds-checks virt_addr < dmabuf->size
    before indexing tx_vec[virt_addr / PAGE_SIZE]. With size =
    N*PAGE_SIZE + r (1 <= r < PAGE_SIZE), sendmsg() at iov_base =
    N*PAGE_SIZE passes the bound check and reads tx_vec[N] -- one past.

  - owner->area.num_niovs = len / PAGE_SIZE while gen_pool_add_owner()
    covers the full byte len, so a non-page-multiple non-final sg
    desyncs num_niovs from the gen_pool 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 tx_vec is sized off dmabuf->size); the
SG-length check covers both directions.

Fixes: bd61848900bf ("net: devmem: Implement TX path")
Cc: stable@vger.kernel.org
Signed-off-by: David Carlier <devnexen@gmail.com>
Reviewed-by: Bobby Eshleman <bobbyeshleman@meta.com>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Reviewed-by: Mina Almasry <almasrymina@google.com>
Link: https://patch.msgid.link/20260519203530.66310-1-devnexen@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>