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![Serge E. Hallyn](/assets/img/avatar_default.png)
As far as I know, all distros currently ship kernels with default CONFIG_SECURITY_FILE_CAPABILITIES=y. Since having the option on leaves a 'no_file_caps' option to boot without file capabilities, the main reason to keep the option is that turning it off saves you (on my s390x partition) 5k. In particular, vmlinux sizes came to: without patch fscaps=n: 53598392 without patch fscaps=y: 53603406 with this patch applied: 53603342 with the security-next tree. Against this we must weigh the fact that there is no simple way for userspace to figure out whether file capabilities are supported, while things like per-process securebits, capability bounding sets, and adding bits to pI if CAP_SETPCAP is in pE are not supported with SECURITY_FILE_CAPABILITIES=n, leaving a bit of a problem for applications wanting to know whether they can use them and/or why something failed. It also adds another subtly different set of semantics which we must maintain at the risk of severe security regressions. So this patch removes the SECURITY_FILE_CAPABILITIES compile option. It drops the kernel size by about 50k over the stock SECURITY_FILE_CAPABILITIES=y kernel, by removing the cap_limit_ptraced_target() function. Changelog: Nov 20: remove cap_limit_ptraced_target() as it's logic was ifndef'ed. Signed-off-by: Serge E. Hallyn <serue@us.ibm.com> Acked-by: Andrew G. Morgan" <morgan@kernel.org> Signed-off-by: James Morris <jmorris@namei.org>
316 lines
8.1 KiB
C
316 lines
8.1 KiB
C
/*
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* linux/kernel/capability.c
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*
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* Copyright (C) 1997 Andrew Main <zefram@fysh.org>
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*
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* Integrated into 2.1.97+, Andrew G. Morgan <morgan@kernel.org>
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* 30 May 2002: Cleanup, Robert M. Love <rml@tech9.net>
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*/
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#include <linux/audit.h>
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#include <linux/capability.h>
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#include <linux/mm.h>
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#include <linux/module.h>
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#include <linux/security.h>
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#include <linux/syscalls.h>
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#include <linux/pid_namespace.h>
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#include <asm/uaccess.h>
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#include "cred-internals.h"
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/*
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* Leveraged for setting/resetting capabilities
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*/
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const kernel_cap_t __cap_empty_set = CAP_EMPTY_SET;
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const kernel_cap_t __cap_full_set = CAP_FULL_SET;
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const kernel_cap_t __cap_init_eff_set = CAP_INIT_EFF_SET;
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EXPORT_SYMBOL(__cap_empty_set);
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EXPORT_SYMBOL(__cap_full_set);
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EXPORT_SYMBOL(__cap_init_eff_set);
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int file_caps_enabled = 1;
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static int __init file_caps_disable(char *str)
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{
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file_caps_enabled = 0;
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return 1;
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}
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__setup("no_file_caps", file_caps_disable);
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/*
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* More recent versions of libcap are available from:
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*
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* http://www.kernel.org/pub/linux/libs/security/linux-privs/
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*/
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static void warn_legacy_capability_use(void)
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{
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static int warned;
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if (!warned) {
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char name[sizeof(current->comm)];
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printk(KERN_INFO "warning: `%s' uses 32-bit capabilities"
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" (legacy support in use)\n",
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get_task_comm(name, current));
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warned = 1;
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}
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}
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/*
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* Version 2 capabilities worked fine, but the linux/capability.h file
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* that accompanied their introduction encouraged their use without
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* the necessary user-space source code changes. As such, we have
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* created a version 3 with equivalent functionality to version 2, but
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* with a header change to protect legacy source code from using
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* version 2 when it wanted to use version 1. If your system has code
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* that trips the following warning, it is using version 2 specific
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* capabilities and may be doing so insecurely.
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*
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* The remedy is to either upgrade your version of libcap (to 2.10+,
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* if the application is linked against it), or recompile your
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* application with modern kernel headers and this warning will go
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* away.
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*/
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static void warn_deprecated_v2(void)
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{
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static int warned;
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if (!warned) {
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char name[sizeof(current->comm)];
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printk(KERN_INFO "warning: `%s' uses deprecated v2"
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" capabilities in a way that may be insecure.\n",
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get_task_comm(name, current));
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warned = 1;
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}
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}
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/*
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* Version check. Return the number of u32s in each capability flag
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* array, or a negative value on error.
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*/
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static int cap_validate_magic(cap_user_header_t header, unsigned *tocopy)
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{
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__u32 version;
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if (get_user(version, &header->version))
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return -EFAULT;
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switch (version) {
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case _LINUX_CAPABILITY_VERSION_1:
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warn_legacy_capability_use();
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*tocopy = _LINUX_CAPABILITY_U32S_1;
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break;
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case _LINUX_CAPABILITY_VERSION_2:
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warn_deprecated_v2();
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/*
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* fall through - v3 is otherwise equivalent to v2.
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*/
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case _LINUX_CAPABILITY_VERSION_3:
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*tocopy = _LINUX_CAPABILITY_U32S_3;
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break;
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default:
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if (put_user((u32)_KERNEL_CAPABILITY_VERSION, &header->version))
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return -EFAULT;
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return -EINVAL;
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}
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return 0;
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}
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/*
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* The only thing that can change the capabilities of the current
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* process is the current process. As such, we can't be in this code
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* at the same time as we are in the process of setting capabilities
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* in this process. The net result is that we can limit our use of
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* locks to when we are reading the caps of another process.
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*/
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static inline int cap_get_target_pid(pid_t pid, kernel_cap_t *pEp,
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kernel_cap_t *pIp, kernel_cap_t *pPp)
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{
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int ret;
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if (pid && (pid != task_pid_vnr(current))) {
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struct task_struct *target;
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read_lock(&tasklist_lock);
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target = find_task_by_vpid(pid);
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if (!target)
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ret = -ESRCH;
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else
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ret = security_capget(target, pEp, pIp, pPp);
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read_unlock(&tasklist_lock);
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} else
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ret = security_capget(current, pEp, pIp, pPp);
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return ret;
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}
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/**
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* sys_capget - get the capabilities of a given process.
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* @header: pointer to struct that contains capability version and
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* target pid data
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* @dataptr: pointer to struct that contains the effective, permitted,
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* and inheritable capabilities that are returned
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*
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* Returns 0 on success and < 0 on error.
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*/
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SYSCALL_DEFINE2(capget, cap_user_header_t, header, cap_user_data_t, dataptr)
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{
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int ret = 0;
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pid_t pid;
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unsigned tocopy;
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kernel_cap_t pE, pI, pP;
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ret = cap_validate_magic(header, &tocopy);
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if ((dataptr == NULL) || (ret != 0))
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return ((dataptr == NULL) && (ret == -EINVAL)) ? 0 : ret;
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if (get_user(pid, &header->pid))
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return -EFAULT;
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if (pid < 0)
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return -EINVAL;
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ret = cap_get_target_pid(pid, &pE, &pI, &pP);
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if (!ret) {
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struct __user_cap_data_struct kdata[_KERNEL_CAPABILITY_U32S];
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unsigned i;
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for (i = 0; i < tocopy; i++) {
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kdata[i].effective = pE.cap[i];
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kdata[i].permitted = pP.cap[i];
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kdata[i].inheritable = pI.cap[i];
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}
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/*
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* Note, in the case, tocopy < _KERNEL_CAPABILITY_U32S,
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* we silently drop the upper capabilities here. This
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* has the effect of making older libcap
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* implementations implicitly drop upper capability
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* bits when they perform a: capget/modify/capset
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* sequence.
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*
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* This behavior is considered fail-safe
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* behavior. Upgrading the application to a newer
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* version of libcap will enable access to the newer
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* capabilities.
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*
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* An alternative would be to return an error here
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* (-ERANGE), but that causes legacy applications to
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* unexpectidly fail; the capget/modify/capset aborts
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* before modification is attempted and the application
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* fails.
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*/
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if (copy_to_user(dataptr, kdata, tocopy
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* sizeof(struct __user_cap_data_struct))) {
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return -EFAULT;
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}
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}
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return ret;
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}
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/**
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* sys_capset - set capabilities for a process or (*) a group of processes
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* @header: pointer to struct that contains capability version and
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* target pid data
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* @data: pointer to struct that contains the effective, permitted,
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* and inheritable capabilities
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*
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* Set capabilities for the current process only. The ability to any other
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* process(es) has been deprecated and removed.
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*
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* The restrictions on setting capabilities are specified as:
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*
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* I: any raised capabilities must be a subset of the old permitted
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* P: any raised capabilities must be a subset of the old permitted
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* E: must be set to a subset of new permitted
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*
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* Returns 0 on success and < 0 on error.
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*/
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SYSCALL_DEFINE2(capset, cap_user_header_t, header, const cap_user_data_t, data)
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{
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struct __user_cap_data_struct kdata[_KERNEL_CAPABILITY_U32S];
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unsigned i, tocopy, copybytes;
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kernel_cap_t inheritable, permitted, effective;
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struct cred *new;
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int ret;
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pid_t pid;
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ret = cap_validate_magic(header, &tocopy);
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if (ret != 0)
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return ret;
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if (get_user(pid, &header->pid))
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return -EFAULT;
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/* may only affect current now */
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if (pid != 0 && pid != task_pid_vnr(current))
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return -EPERM;
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copybytes = tocopy * sizeof(struct __user_cap_data_struct);
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if (copybytes > sizeof(kdata))
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return -EFAULT;
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if (copy_from_user(&kdata, data, copybytes))
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return -EFAULT;
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for (i = 0; i < tocopy; i++) {
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effective.cap[i] = kdata[i].effective;
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permitted.cap[i] = kdata[i].permitted;
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inheritable.cap[i] = kdata[i].inheritable;
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}
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while (i < _KERNEL_CAPABILITY_U32S) {
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effective.cap[i] = 0;
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permitted.cap[i] = 0;
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inheritable.cap[i] = 0;
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i++;
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}
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new = prepare_creds();
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if (!new)
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return -ENOMEM;
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ret = security_capset(new, current_cred(),
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&effective, &inheritable, &permitted);
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if (ret < 0)
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goto error;
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audit_log_capset(pid, new, current_cred());
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return commit_creds(new);
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error:
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abort_creds(new);
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return ret;
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}
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/**
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* capable - Determine if the current task has a superior capability in effect
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* @cap: The capability to be tested for
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*
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* Return true if the current task has the given superior capability currently
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* available for use, false if not.
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*
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* This sets PF_SUPERPRIV on the task if the capability is available on the
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* assumption that it's about to be used.
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*/
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int capable(int cap)
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{
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if (unlikely(!cap_valid(cap))) {
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printk(KERN_CRIT "capable() called with invalid cap=%u\n", cap);
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BUG();
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}
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if (security_capable(cap) == 0) {
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current->flags |= PF_SUPERPRIV;
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return 1;
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}
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return 0;
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}
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EXPORT_SYMBOL(capable);
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