`virtio_transport_stream_do_peek`, when calculating the number of bytes to
copy, didn't consider the `offset`, caused by partial reads that happened
before.
This might cause out-of-bounds read that lead to an EFAULT.
More details in the commits.

Commit 1 introduces the fix
Commit 2 introduces some preliminary work for adding a test
Commit 3 introduces a test that checks for this bug to avoid future
regressions.

Signed-off-by: Luigi Leonardi <leonardi@redhat.com>
---
Changes in v2:
- Addressed reviewers comment
    - Test now uses the recv_buf utils.
    - Removed unnecessary barrier
    - Checkpatch warnings.
- Added new commit that allows to use recv_buf with MSG_PEEK
- Picked up RoBs
- Link to v1: https://lore.kernel.org/r/20260402-fix_peek-v1-0-ad274fcef77b@redhat.com

---
Luigi Leonardi (3):
      vsock/virtio: fix MSG_PEEK ignoring skb offset when calculating bytes to copy
      vsock/test: handle MSG_PEEK in `recv_buf`
      vsock/test: add MSG_PEEK after partial recv test

 net/vmw_vsock/virtio_transport_common.c |  5 ++-
 tools/testing/vsock/util.c              |  8 +++++
 tools/testing/vsock/vsock_test.c        | 56 ++++++++++++++++++++++++++-------
 3 files changed, 54 insertions(+), 15 deletions(-)
---
base-commit: bfe62a454542cfad3379f6ef5680b125f41e20f4
change-id: 20260401-fix_peek-6837b83469e3

Best regards,
-- 
Luigi Leonardi <leonardi@redhat.com>