preadv(2), pwrite(2): validate uio_resid

[kib]

Summary

It should be greater than zero, and less than IOSIZE_MAX. Remove now redundand checks from functions calling kern_preadv() and kern_pwritev(), i.e. read/pread and write/pwrite syscalls implementations.

[markj]

Why is the checking in copyinuio() not sufficient?

[kib]

In D29747#667120, @markj wrote:

Why is the checking in copyinuio() not sufficient?

iov_len is size_t, while uio_resid is ssize_t. When IOSIZE_MAX is unclamped, the checks in copyinuio() probably do not check much.

I think at least iov_len should be verified to fit into ssize_t, but still I believe that the final check for uio_resid in dofileread/write is useful.

[kib]

Also check that each iov_len can fit into uio_resid.

[pho]

This patch does not fix the issue for me using this test scenario:

pwrite.sh2 KBDownload

https://people.freebsd.org/~pho/stress/log/log0091.txt