[PATCH net v4 0/3] vsock/virtio: fix MSG_PEEK calculation on bytes to copy

[Luigi Leonardi <leonardi@redhat.com>]

`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 and fixes a
problem in existing tests.
Commit 3 introduces a test that checks for this bug to avoid future
regressions.

For disclosure: this bug was found initially by claude opus 4.6, I then analyzed
it and worked on the fix and the test.

Signed-off-by: Luigi Leonardi <leonardi@redhat.com>
---
Changes in v4:
- Picked up RoB
- Increased sleep time from 10 us to 10 ms
- Minor changes to commit messages and comments as suggested by Stefano.
- Link to v3: https://lore.kernel.org/r/20260414-fix_peek-v3-0-e7daead49f83@redhat.com

Changes in v3:
- Addressed reviwers omment
    - Dropped test client, reusing the one already existing
    - Minor changes: added comment, improved commit messages
    - Rebased to latest net-next
- Link to v2: https://lore.kernel.org/r/20260407-fix_peek-v2-0-2e2581dc8b7c@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: fix MSG_PEEK handling 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              | 15 ++++++++++
 tools/testing/vsock/vsock_test.c        | 50 +++++++++++++++++++++++++--------
 3 files changed, 55 insertions(+), 15 deletions(-)
---
base-commit: 35c2c39832e569449b9192fa1afbbc4c66227af7
change-id: 20260401-fix_peek-6837b83469e3

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