This is part 2 of the v2 port-entry-limit series. Part 1 (gnumach:
configurable cur/max port-entry limit) was posted earlier today.
Part 2 is the glibc half: expose the kernel limit to userspace as a new
resource, RLIMIT_PORT_ENTRY, and keep it in sync with the kernel.
- bits/resource.h: new resource RLIMIT_PORT_ENTRY. It is added to the
generic (non-Linux) resource list, before RLIMIT_NLIMITS, so the
existing resource numbers do not move; only RLIM_NLIMITS grows by
one. If you would rather keep this Hurd-only, say so and I will
move it into a sysdeps/mach/hurd override instead.
- sysdeps/mach/hurd/setrlimit.c: forward changes to
__task_set_port_entry_limit, mirroring the existing RLIMIT_AS path
through __vm_set_size_limit. Raising the hard limit needs the
privileged host control port (__get_privileged_ports); lowering it
works with the ordinary host port. KERN_NO_ACCESS maps to EPERM.
- hurd/hurdrlimit.c: seed _hurd_rlimits[RLIMIT_PORT_ENTRY] from
TASK_PORT_ENTRY_LIMIT_INFO at startup, so getrlimit reports the real
kernel cur/max instead of an invented one.
- sysdeps/mach/configure.ac: check for task_set_port_entry_limit in
gnumach.defs (HAVE_MACH_TASK_SET_PORT_ENTRY_LIMIT). The generated
configure fragment is included in the diff by hand, because this box
only has autoconf 2.71 and glibc wants 2.72; it should be regenerated
before anyone commits it.
One thing worth stating explicitly, because it changes what the patch
needs to do: no _Fork change is required for inheritance. fork() on the
Hurd copies the whole address space, so the child already gets a copy of
_hurd_rlimits; and the kernel side is inherited in the gnumach half when
the child task's IPC space is created, the same way vm_map_fork inherits
size_cur_limit/size_max_limit. So parent-to-child propagation falls out
of the two halves together. If you would rather have _Fork set the
child's limit explicitly as well, I can add that, but it looked
redundant.
Open question I still have, repeated from my reply in the part 1 thread:
RLIMIT vs a Mach-native interface. This half assumes RLIMIT because it
fits the existing setrlimit/getrlimit plumbing and your point about the
resource utilities. If you prefer the Mach-native shape only, the
gnumach half still stands on its own and this half can be dropped.
Verified: the diff applies cleanly at glibc HEAD 04a3995.
Same caveat as part 1: I cannot sign FSF papers, so this is public
analysis rather than a submission. A contributor who has signed is free
to carry it.
Sylvia
--- 8< ---
>From 8f7f6b4e6b09ba65b7c42d65280008d70b99c6ee Mon Sep 17 00:00:00 2001
From: Sylvia <[email protected]>
Date: Thu, 24 Sep 2026 21:04:52 +0000
Subject: [PATCH] hurd: add RLIMIT_PORT_ENTRY for the gnumach port-entry limit
The gnumach task_set_port_entry_limit RPC caps the number of entries in
a task's IPC space, and TASK_PORT_ENTRY_LIMIT_INFO reports the current
and maximum values. This is the glibc half of that pair, and it mirrors
the existing vm_set_size_limit / vm_get_size_limit handling for the
address space.
Expose the limit to userspace as a new resource, RLIMIT_PORT_ENTRY:
* bits/resource.h: add the resource.
* sysdeps/mach/hurd/setrlimit.c: forward changes to
__task_set_port_entry_limit. Raising the hard limit needs the
privileged host control port, exactly as raising RLIMIT_AS does;
lowering it works with the ordinary host port.
* hurd/hurdrlimit.c: seed the limit from the kernel at startup.
* sysdeps/mach/configure.ac: check for the new RPC.
Inheritance across fork(2) needs no change in _Fork: the child is a
copy-on-write copy of the parent's address space, so it gets a copy of
_hurd_rlimits, and the kernel side is inherited by the IPC space code
when the child task is created (the same way vm_map_fork inherits the
address-space limits).
---
bits/resource.h | 6 ++++++
hurd/hurdrlimit.c | 13 +++++++++++++
sysdeps/mach/configure | 30 ++++++++++++++++++++++++++++++
sysdeps/mach/configure.ac | 2 ++
sysdeps/mach/hurd/setrlimit.c | 35 ++++++++++++++++++++++++++++++++++-
5 files changed, 85 insertions(+), 1 deletion(-)
diff --git a/bits/resource.h b/bits/resource.h
index 6b83374..3972da3 100644
--- a/bits/resource.h
+++ b/bits/resource.h
@@ -70,6 +70,12 @@ enum __rlimit_resource
RLIMIT_VMEM = RLIMIT_AS, /* Another name for the same thing. */
#define RLIMIT_AS RLIMIT_AS
#define RLIMIT_VMEM RLIMIT_AS
+ /* Maximum number of port entries (Mach port names) a task may hold.
+ This is a GNU/Hurd extension: it caps the kernel IPC space, so a
+ task that leaks ports exhausts its own space instead of the
+ machine's memory. */
+ RLIMIT_PORT_ENTRY,
+#define RLIMIT_PORT_ENTRY RLIMIT_PORT_ENTRY
RLIMIT_NLIMITS, /* Number of limit flavors. */
RLIM_NLIMITS = RLIMIT_NLIMITS /* Traditional name for same. */
diff --git a/hurd/hurdrlimit.c b/hurd/hurdrlimit.c
index 8de5520..140816b 100644
--- a/hurd/hurdrlimit.c
+++ b/hurd/hurdrlimit.c
@@ -46,6 +46,19 @@ init_rlimit (void)
}
#endif
+#ifdef TASK_PORT_ENTRY_LIMIT_INFO
+ {
+ task_port_entry_limit_info_data_t info;
+ mach_msg_type_number_t count = TASK_PORT_ENTRY_LIMIT_INFO_COUNT;
+ if (__task_info (__mach_task_self (), TASK_PORT_ENTRY_LIMIT_INFO,
+ (task_info_t) &info, &count) == KERN_SUCCESS)
+ {
+ _hurd_rlimits[RLIMIT_PORT_ENTRY].rlim_cur = info.cur_limit;
+ _hurd_rlimits[RLIMIT_PORT_ENTRY].rlim_max = info.max_limit;
+ }
+ }
+#endif
+
for (i = 0; i < RLIM_NLIMITS; ++i)
{
if (_hurd_rlimits[i].rlim_max == 0)
diff --git a/sysdeps/mach/configure b/sysdeps/mach/configure
index a725cd1..a199799 100755
--- a/sysdeps/mach/configure
+++ b/sysdeps/mach/configure
@@ -641,6 +641,36 @@ if test $libc_cv_mach_rpc_vm_get_size_limit = yes; then
fi
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for
task_set_port_entry_limit in gnumach.defs" >&5
+printf %s "checking for task_set_port_entry_limit in gnumach.defs... " >&6; }
+if test ${libc_cv_mach_rpc_task_set_port_entry_limit+y}
+then :
+ printf %s "(cached) " >&6
+else case e in #(
+ e) cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h. */
+#include <mach/gnumach.defs>
+
+_ACEOF
+if (eval "$ac_cpp conftest.$ac_ext") 2>&5 |
+ $EGREP_TRADITIONAL "task_set_port_entry_limit" >/dev/null 2>&1
+then :
+ libc_cv_mach_rpc_task_set_port_entry_limit=yes
+else case e in #(
+ e) libc_cv_mach_rpc_task_set_port_entry_limit=no ;;
+esac
+fi
+rm -rf conftest*
+ ;;
+esac
+fi
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: result:
$libc_cv_mach_rpc_task_set_port_entry_limit" >&5
+printf "%s\n" "$libc_cv_mach_rpc_task_set_port_entry_limit" >&6; }
+if test $libc_cv_mach_rpc_task_set_port_entry_limit = yes; then
+ printf "%s\n" "#define HAVE_MACH_TASK_SET_PORT_ENTRY_LIMIT 1" >>confdefs.h
+
+fi
+
{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for task_max_priority
in mach_host.defs" >&5
printf %s "checking for task_max_priority in mach_host.defs... " >&6; }
if test ${libc_cv_mach_rpc_task_max_priority+y}
diff --git a/sysdeps/mach/configure.ac b/sysdeps/mach/configure.ac
index b591e6f..085ab3c 100644
--- a/sysdeps/mach/configure.ac
+++ b/sysdeps/mach/configure.ac
@@ -104,6 +104,8 @@ mach_RPC_CHECK(gnumach.defs, vm_set_size_limit,
HAVE_MACH_VM_SET_SIZE_LIMIT)
mach_RPC_CHECK(gnumach.defs, vm_get_size_limit,
HAVE_MACH_VM_GET_SIZE_LIMIT)
+mach_RPC_CHECK(gnumach.defs, task_set_port_entry_limit,
+ HAVE_MACH_TASK_SET_PORT_ENTRY_LIMIT)
mach_RPC_CHECK(mach_host.defs, task_max_priority,
HAVE_MACH_TASK_MAX_PRIORITY)
diff --git a/sysdeps/mach/hurd/setrlimit.c b/sysdeps/mach/hurd/setrlimit.c
index 4277b25..4a41d9f 100644
--- a/sysdeps/mach/hurd/setrlimit.c
+++ b/sysdeps/mach/hurd/setrlimit.c
@@ -78,9 +78,42 @@ retry:
}
#endif
+#ifdef HAVE_MACH_TASK_SET_PORT_ENTRY_LIMIT
+ if (resource == RLIMIT_PORT_ENTRY)
+ {
+ if (host == MACH_PORT_NULL)
+ {
+ /* Raising the hard limit needs the privileged host control
+ port; lowering it is allowed with the ordinary one. */
+ if (_hurd_rlimits[resource].rlim_max < lim.rlim_max)
+ {
+ err = __get_privileged_ports (&host, NULL);
+ if (err)
+ goto fail;
+ }
+ else
+ host = __mach_host_self ();
+ }
+
+ err = __task_set_port_entry_limit (host, __mach_task_self (),
+ lim.rlim_cur, lim.rlim_max);
+
+ if (err == MIG_BAD_ID)
+ /* MIG_BAD_ID returned as kernel support is missing, clear error */
+ err = 0;
+ else if (err)
+ {
+ if (err == KERN_NO_ACCESS)
+ err = EPERM;
+ goto fail;
+ }
+ }
+#endif
+
_hurd_rlimits[resource] = lim;
-#ifdef HAVE_MACH_VM_SET_SIZE_LIMIT
+#if defined (HAVE_MACH_VM_SET_SIZE_LIMIT) \
+ || defined (HAVE_MACH_TASK_SET_PORT_ENTRY_LIMIT)
fail:
#endif
__mutex_unlock (&_hurd_rlimit_lock);
--
2.39.5
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