Allow getdtablesize in capability mode

[emaste]

Summary

It is a legacy interface that is equivalent to (already permitted) getrlimit with the RLIMIT_NOFILE option.

[emaste]

sys/kern/capabilities.conf

33 ↗

(On Diff #19872)

As an aside this is mostly, but not entirely, true. The cases where it's not true (e.g. __cap_rights_get, the "Operations relative to directory capabilities") make sense to me, and I wonder if we shouldn't instead have a handful of alphabetically sorted groups?

[emaste]

And will makesyscalls.sh afterwards, which results in

diff --git a/sys/kern/init_sysent.c b/sys/kern/init_sysent.c
index 6be4769..907d3ea 100644
--- a/sys/kern/init_sysent.c
+++ b/sys/kern/init_sysent.c
@@ -135,7 +135,7 @@ struct sysent sysent[] = {
        { AS(getitimer_args), (sy_call_t *)sys_getitimer, AUE_GETITIMER, NULL, 0, 0, SYF_CAPENABLED, SY_THR_STATIC },   /* 86 = getitimer */
        { compat(AS(gethostname_args),gethostname), AUE_SYSCTL, NULL, 0, 0, SYF_CAPENABLED, SY_THR_STATIC },    /* 87 = old gethostname */
        { compat(AS(sethostname_args),sethostname), AUE_SYSCTL, NULL, 0, 0, 0, SY_THR_STATIC }, /* 88 = old sethostname */
-       { 0, (sy_call_t *)sys_getdtablesize, AUE_GETDTABLESIZE, NULL, 0, 0, 0, SY_THR_STATIC }, /* 89 = getdtablesize */
+       { 0, (sy_call_t *)sys_getdtablesize, AUE_GETDTABLESIZE, NULL, 0, 0, SYF_CAPENABLED, SY_THR_STATIC },    /* 89 = getdtablesize */
        { AS(dup2_args), (sy_call_t *)sys_dup2, AUE_DUP2, NULL, 0, 0, SYF_CAPENABLED, SY_THR_STATIC },  /* 90 = dup2 */
        { 0, (sy_call_t *)nosys, AUE_NULL, NULL, 0, 0, 0, SY_THR_ABSENT },                      /* 91 = getdopt */
        { AS(fcntl_args), (sy_call_t *)sys_fcntl, AUE_FCNTL, NULL, 0, 0, SYF_CAPENABLED, SY_THR_STATIC },       /* 92 = fcntl */

[emaste]

@jilles has informed me (via D7720) it's not exactly equivalent to getrlimit(RLIMIT_NOFILE), but it is still trivial global state that should be allowed in capability mode for the same reason as getrlimit.