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SubjectRe: [PATCH] Realtime LSM
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Date
Jody McIntyre <realtime-lsm@modernduck.com> writes:

> This patch still includes allcaps, which should be removed before it is
> merged.

The `allcaps' option is removed in this version, documentation
updated, plus some minor comment changes.

> The patch is now against 2.6.9-pre2-mm4.

This patch was diff'ed against 2.6.8.1. Some of the offsets in
2.6.9-pre2-mm4 were slightly different, but the patch applied
correctly anyway. I think it will work fine either way.

> The realtime-lsm Linux Security Module, written by Torben Hohn and Jack
> O'Quin, selectively grants realtime capabilities to specific user groups
> or applications. The typical use for this is low latency audio, and the
> patch has been extensively field tested by Linux audio users. The
> realtime LSM is a major improvement in security over the 2.4 capablities
> patch and other workarounds like jackstart, which rely on CAP_SETPCAP.
>
> Signed-Off-By: Lee Revell <rlrevell@joe-job.com>
> Signed-off-by: Jody McIntyre <realtime-lsm@modernduck.com>

Signed-off-by: Jack O'Quin <joq@joq.us>

diff -ruN -X /home/joq/bin/kdiff.exclude linux-2.6.8.1/Documentation/realtime-lsm.txt linux-2.6.8.1-rt02/Documentation/realtime-lsm.txt
--- linux-2.6.8.1/Documentation/realtime-lsm.txt Wed Dec 31 18:00:00 1969
+++ linux-2.6.8.1-rt02/Documentation/realtime-lsm.txt Mon Oct 4 21:38:26 2004
@@ -0,0 +1,38 @@
+
+ Realtime Linux Security Module
+
+
+This Linux Security Module (LSM) enables realtime capabilities. It
+was written by Torben Hohn and Jack O'Quin, under the provisions of
+the GPL (see the COPYING file). We make no warranty concerning the
+safety, security or even stability of your system when using it. But,
+we will fix problems if you report them.
+
+Once the LSM has been installed and the kernel for which it was built
+is running, the root user can load it and pass parameters as follows:
+
+ # modprobe realtime any=1
+
+ Any program can request realtime privileges. This allows any local
+ user to crash the system by hogging the CPU in a tight loop or
+ locking down too much memory. But, it is simple to administer. :-)
+
+ # modprobe realtime gid=29
+
+ All users belonging to group 29 and programs that are setgid to that
+ group have realtime privileges. Use any group number you like. A
+ `gid' of -1 disables group access.
+
+ # modprobe realtime mlock=0
+
+ Grants realtime scheduling privileges without the ability to lock
+ memory using mlock() or mlockall() system calls. This option can be
+ used in conjunction with any of the other options.
+
+Parameters can be changed dynamically via /proc/sys/security/realtime:
+
+ # sysctl -w security/realtime/any=0
+ # sysctl -w security/realtime/gid=29
+ # sysctl -w security/realtime/mlock=1
+
+Jack O'Quin, joq@joq.us
diff -ruN -X /home/joq/bin/kdiff.exclude linux-2.6.8.1/include/linux/sysctl.h linux-2.6.8.1-rt02/include/linux/sysctl.h
--- linux-2.6.8.1/include/linux/sysctl.h Sat Aug 14 05:55:33 2004
+++ linux-2.6.8.1-rt02/include/linux/sysctl.h Sun Oct 3 10:56:16 2004
@@ -61,7 +61,14 @@
CTL_DEV=7, /* Devices */
CTL_BUS=8, /* Busses */
CTL_ABI=9, /* Binary emulation */
- CTL_CPU=10 /* CPU stuff (speed scaling, etc) */
+ CTL_CPU=10, /* CPU stuff (speed scaling, etc) */
+ CTL_SECURITY=11 /* Security modules */
+};
+
+/* CTL_SECURITY names: */
+enum
+{
+ SECURITY_REALTIME=1 /* Realtime LSM */
};

/* CTL_BUS names: */
diff -ruN -X /home/joq/bin/kdiff.exclude linux-2.6.8.1/security/Kconfig linux-2.6.8.1-rt02/security/Kconfig
--- linux-2.6.8.1/security/Kconfig Sat Aug 14 05:55:47 2004
+++ linux-2.6.8.1-rt02/security/Kconfig Sun Oct 3 10:56:17 2004
@@ -44,6 +44,17 @@

If you are unsure how to answer this question, answer N.

+config SECURITY_REALTIME
+ tristate "Realtime Capabilities"
+ depends on SECURITY && SECURITY_CAPABILITIES!=y
+ default n
+ help
+ This module selectively grants realtime privileges
+ controlled by load-time parameters and
+ /proc/sys/security/realtime.
+
+ If you are unsure how to answer this question, answer N.
+
source security/selinux/Kconfig

endmenu
diff -ruN -X /home/joq/bin/kdiff.exclude linux-2.6.8.1/security/Makefile linux-2.6.8.1-rt02/security/Makefile
--- linux-2.6.8.1/security/Makefile Sat Aug 14 05:55:48 2004
+++ linux-2.6.8.1-rt02/security/Makefile Sun Oct 3 10:56:16 2004
@@ -15,3 +15,4 @@
obj-$(CONFIG_SECURITY_SELINUX) += selinux/built-in.o
obj-$(CONFIG_SECURITY_CAPABILITIES) += commoncap.o capability.o
obj-$(CONFIG_SECURITY_ROOTPLUG) += commoncap.o root_plug.o
+obj-$(CONFIG_SECURITY_REALTIME) += commoncap.o realtime.o
diff -ruN -X /home/joq/bin/kdiff.exclude linux-2.6.8.1/security/realtime.c linux-2.6.8.1-rt02/security/realtime.c
--- linux-2.6.8.1/security/realtime.c Wed Dec 31 18:00:00 1969
+++ linux-2.6.8.1-rt02/security/realtime.c Mon Oct 4 21:35:41 2004
@@ -0,0 +1,267 @@
+/*
+ * Realtime Capabilities Linux Security Module
+ *
+ * Copyright (C) 2003 Torben Hohn
+ * Copyright (C) 2003, 2004 Jack O'Quin
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ */
+
+#include <linux/config.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/security.h>
+#include <linux/file.h>
+#include <linux/mm.h>
+#include <linux/mman.h>
+#include <linux/pagemap.h>
+#include <linux/swap.h>
+#include <linux/smp_lock.h>
+#include <linux/skbuff.h>
+#include <linux/netlink.h>
+#include <linux/ptrace.h>
+#include <linux/sysctl.h>
+
+#ifdef CONFIG_SECURITY
+
+#define RT_LSM "Realtime LSM " /* syslog module name prefix */
+#define RT_ERR "Realtime: " /* syslog error message prefix */
+
+#include <linux/vermagic.h>
+MODULE_INFO(vermagic,VERMAGIC_STRING);
+
+/* this is needed for the proc_dointvec_minmax for allowed GID */
+static int maxuid = 65535;
+static int minuid = -1;
+
+/* module parameters
+ *
+ * These values could change at any time due to some process writing
+ * a new value to /proc/sys/security/realtime. This is OK, because
+ * each is referenced only once in each function call. Nothing
+ * depends on parameters having the same value every time.
+ */
+static int any = 0; /* if TRUE, any process is realtime */
+MODULE_PARM(any, "i");
+MODULE_PARM_DESC(any, " grant realtime privileges to any process.");
+
+static int gid = -1; /* realtime group id, or NO_GROUP */
+MODULE_PARM(gid, "i");
+MODULE_PARM_DESC(gid, " the group ID with access to realtime privileges.");
+
+static int mlock = 1; /* enable mlock() privileges */
+MODULE_PARM(mlock, "i");
+MODULE_PARM_DESC(mlock, " enable memory locking privileges.");
+
+/* helper function for testing group membership */
+static inline int gid_ok(int gid, int e_gid) {
+ int i;
+ int rt_ok = 0;
+
+ if (gid == -1)
+ return 0;
+
+ if ((gid == e_gid) || (gid == current->gid))
+ return 1;
+
+ get_group_info(current->group_info);
+ for (i = 0; i < current->group_info->ngroups; ++i) {
+ if (gid == GROUP_AT(current->group_info, i)) {
+ rt_ok = 1;
+ break;
+ }
+ }
+ put_group_info(current->group_info);
+
+ return rt_ok;
+}
+
+int realtime_bprm_set_security(struct linux_binprm *bprm)
+{
+ /* Copied from security/commoncap.c: cap_bprm_set_security()... */
+ /* Copied from fs/exec.c:prepare_binprm. */
+ /* We don't have VFS support for capabilities yet */
+ cap_clear(bprm->cap_inheritable);
+ cap_clear(bprm->cap_permitted);
+ cap_clear(bprm->cap_effective);
+
+ /* If a non-zero `any' parameter was specified, we grant
+ * realtime privileges to every process. If the `gid'
+ * parameter was specified and it matches the group id of the
+ * executable, of the current process or any supplementary
+ * groups, we grant realtime capabilites.
+ */
+
+ if (any || gid_ok(gid, bprm->e_gid)) {
+ cap_raise(bprm->cap_effective, CAP_SYS_NICE);
+ cap_raise(bprm->cap_permitted, CAP_SYS_NICE);
+ if (mlock) {
+ cap_raise(bprm->cap_effective, CAP_IPC_LOCK);
+ cap_raise(bprm->cap_permitted, CAP_IPC_LOCK);
+ cap_raise(bprm->cap_effective,
+ CAP_SYS_RESOURCE);
+ cap_raise(bprm->cap_permitted,
+ CAP_SYS_RESOURCE);
+ }
+ }
+
+ /* To support inheritance of root-permissions and suid-root
+ * executables under compatibility mode, we raise all three
+ * capability sets for the file.
+ *
+ * If only the real uid is 0, we only raise the inheritable
+ * and permitted sets of the executable file.
+ */
+
+ if (bprm->e_uid == 0 || current->uid == 0) {
+ cap_set_full(bprm->cap_inheritable);
+ cap_set_full(bprm->cap_permitted);
+ }
+ if (bprm->e_uid == 0)
+ cap_set_full(bprm->cap_effective);
+
+ return 0;
+}
+
+static struct security_operations capability_ops = {
+ .ptrace = cap_ptrace,
+ .capget = cap_capget,
+ .capset_check = cap_capset_check,
+ .capset_set = cap_capset_set,
+ .capable = cap_capable,
+ .netlink_send = cap_netlink_send,
+ .netlink_recv = cap_netlink_recv,
+ .bprm_apply_creds = cap_bprm_apply_creds,
+ .bprm_set_security = realtime_bprm_set_security,
+ .bprm_secureexec = cap_bprm_secureexec,
+ .task_post_setuid = cap_task_post_setuid,
+ .task_reparent_to_init = cap_task_reparent_to_init,
+ .syslog = cap_syslog,
+ .vm_enough_memory = cap_vm_enough_memory,
+};
+
+#define MY_NAME __stringify(KBUILD_MODNAME)
+
+static ctl_table realtime_table[] =
+{
+ { .ctl_name = 1,
+ .procname = "any",
+ .data = &any,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = &proc_dointvec,
+ },
+ { .ctl_name = 2,
+ .procname = "gid",
+ .data = &gid,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = &proc_dointvec_minmax,
+ .extra1 = &minuid,
+ .extra2 = &maxuid
+ },
+ { .ctl_name = 3,
+ .procname = "mlock",
+ .data = &mlock,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = &proc_dointvec,
+ },
+ { }
+};
+
+static ctl_table realtime_root_table[] =
+{
+ { .ctl_name = SECURITY_REALTIME,
+ .procname = "realtime",
+ .mode = 0555,
+ .child = realtime_table },
+ { }
+};
+
+static ctl_table security_root_table[] =
+{
+ { .ctl_name = CTL_SECURITY,
+ .procname = "security",
+ .mode = 0555,
+ .child = realtime_root_table },
+ { }
+};
+
+static struct ctl_table_header *sysctl_header;
+
+static void __exit exit_sysctl(void)
+{
+ unregister_sysctl_table(sysctl_header);
+}
+
+static int secondary; /* flag to keep track of how we were registered */
+
+static void __exit exit_security(void)
+{
+ /* remove ourselves from the security framework */
+ if (secondary) {
+ if (mod_unreg_security(MY_NAME, &capability_ops))
+ printk(KERN_INFO RT_ERR "Failure unregistering "
+ "capabilities with primary module.\n");
+
+ } else if (unregister_security(&capability_ops)) {
+ printk(KERN_INFO RT_ERR
+ "Failure unregistering capabilities with the kernel\n");
+ }
+ printk(KERN_INFO "Realtime Capability LSM exiting\n");
+}
+
+static int __init capability_init(void)
+{
+ /* register ourselves with the security framework */
+ if (register_security(&capability_ops)) {
+
+ /* try registering with primary module */
+ if (mod_reg_security(MY_NAME, &capability_ops)) {
+ printk(KERN_INFO RT_ERR "Failure registering "
+ "capabilities with primary security module.\n");
+ printk(KERN_INFO RT_ERR "Is kernel configured "
+ "with CONFIG_SECURITY_CAPABILITIES=m?\n");
+ return -EINVAL;
+ }
+ secondary = 1;
+ }
+
+ sysctl_header = register_sysctl_table(security_root_table, 0);
+ if (!sysctl_header) {
+ exit_security();
+ return -ENOMEM;
+ }
+
+ if (any)
+ printk(KERN_INFO RT_LSM
+ "initialized (all groups, mlock=%d)\n", mlock);
+ else if (gid == -1)
+ printk(KERN_INFO RT_LSM
+ "initialized (no groups, mlock=%d)\n", mlock);
+ else
+ printk(KERN_INFO RT_LSM
+ "initialized (group %d, mlock=%d)\n", gid, mlock);
+
+ return 0;
+}
+
+static void __exit capability_exit(void)
+{
+ exit_sysctl();
+ exit_security();
+}
+
+late_initcall(capability_init);
+module_exit(capability_exit);
+
+MODULE_DESCRIPTION("Realtime Capabilities Security Module");
+MODULE_LICENSE("GPL");
+
+#endif /* CONFIG_SECURITY */
--
joq
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