vsock: prevent null-ptr-deref in vsock_*[has_data|has_space]

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: vsock: prevent null-ptr-deref in vsock_*[has_data|has_space] Recent reports have shown how we sometimes call vsock_*_has_data() when a vsock socket has been de-assigned from a transport (see attached links), but we shouldn't. Previous commits should have solved the real problems, but we may have more in the future, so to avoid null-ptr-deref, we can return 0 (no space, no data available) but with a warning. This way the code should continue to run in a nearly consistent state and have a warning that allows us to debug future problems.

References

• https://git.kernel.org/stable/c/daeac89cdb03d30028186f5ff7dc26ec8fa843e7
• https://git.kernel.org/stable/c/9e5fed46ccd2c34c5fa5a9c8825ce4823fdc853e
• https://git.kernel.org/stable/c/b52e50dd4fabd12944172bd486a4f4853b7f74dd
• https://git.kernel.org/stable/c/bc9c49341f9728c31fe248c5fbba32d2e81a092b
• https://git.kernel.org/stable/c/c23d1d4f8efefb72258e9cedce29de10d057f8ca
• https://git.kernel.org/stable/c/91751e248256efc111e52e15115840c35d85abaf