ptrace: Validate error numbers passed to PT_SET_SC_RET

[markj]

Summary

Otherwise OOB reads are possible if one targets a Linux ABI process,
since bsd_to_linux_errno() doesn't validate bounds.

Disallow negative error numbers, as I can't see an obvious reason to
allow injecting them.

Reported by: Dennys Kaluzny Pereira <[e-mail]>
Fixes: fd5faa5629ae ("ptrace(2): PT_SET_SC_RET request")

[kib]

sys/kern/sys_process.c

1494

ERESTART is a useful error to inject.

IMO it is better to check the bounds in linuxulotar.