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2813893f8b
There are a lot of embedded systems that run most or all of their functionality in init, running as root:root. For these systems, supporting multiple users is not necessary. This patch adds a new symbol, CONFIG_MULTIUSER, that makes support for non-root users, non-root groups, and capabilities optional. It is enabled under CONFIG_EXPERT menu. When this symbol is not defined, UID and GID are zero in any possible case and processes always have all capabilities. The following syscalls are compiled out: setuid, setregid, setgid, setreuid, setresuid, getresuid, setresgid, getresgid, setgroups, getgroups, setfsuid, setfsgid, capget, capset. Also, groups.c is compiled out completely. In kernel/capability.c, capable function was moved in order to avoid adding two ifdef blocks. This change saves about 25 KB on a defconfig build. The most minimal kernels have total text sizes in the high hundreds of kB rather than low MB. (The 25k goes down a bit with allnoconfig, but not that much. The kernel was booted in Qemu. All the common functionalities work. Adding users/groups is not possible, failing with -ENOSYS. Bloat-o-meter output: add/remove: 7/87 grow/shrink: 19/397 up/down: 1675/-26325 (-24650) [akpm@linux-foundation.org: coding-style fixes] Signed-off-by: Iulia Manda <iulia.manda21@gmail.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org> Acked-by: Geert Uytterhoeven <geert@linux-m68k.org> Tested-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
450 lines
12 KiB
C
450 lines
12 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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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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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/export.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 <linux/user_namespace.h>
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#include <asm/uaccess.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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EXPORT_SYMBOL(__cap_empty_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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#ifdef CONFIG_MULTIUSER
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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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char name[sizeof(current->comm)];
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pr_info_once("warning: `%s' uses 32-bit capabilities (legacy support in use)\n",
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get_task_comm(name, current));
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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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char name[sizeof(current->comm)];
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pr_info_once("warning: `%s' uses deprecated v2 capabilities in a way that may be insecure\n",
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get_task_comm(name, current));
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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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rcu_read_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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rcu_read_unlock();
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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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* unexpectedly 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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effective.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK;
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permitted.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK;
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inheritable.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK;
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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(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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* has_ns_capability - Does a task have a capability in a specific user ns
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* @t: The task in question
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* @ns: target user namespace
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* @cap: The capability to be tested for
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*
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* Return true if the specified task has the given superior capability
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* currently in effect to the specified user namespace, false if not.
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*
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* Note that this does not set PF_SUPERPRIV on the task.
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*/
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bool has_ns_capability(struct task_struct *t,
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struct user_namespace *ns, int cap)
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{
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int ret;
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rcu_read_lock();
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ret = security_capable(__task_cred(t), ns, cap);
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rcu_read_unlock();
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return (ret == 0);
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}
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/**
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* has_capability - Does a task have a capability in init_user_ns
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* @t: The task in question
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* @cap: The capability to be tested for
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*
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* Return true if the specified task has the given superior capability
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* currently in effect to the initial user namespace, false if not.
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*
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* Note that this does not set PF_SUPERPRIV on the task.
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*/
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bool has_capability(struct task_struct *t, int cap)
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{
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return has_ns_capability(t, &init_user_ns, cap);
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}
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/**
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* has_ns_capability_noaudit - Does a task have a capability (unaudited)
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* in a specific user ns.
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* @t: The task in question
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* @ns: target user namespace
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* @cap: The capability to be tested for
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*
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* Return true if the specified task has the given superior capability
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* currently in effect to the specified user namespace, false if not.
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* Do not write an audit message for the check.
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*
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* Note that this does not set PF_SUPERPRIV on the task.
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*/
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bool has_ns_capability_noaudit(struct task_struct *t,
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struct user_namespace *ns, int cap)
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{
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int ret;
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rcu_read_lock();
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ret = security_capable_noaudit(__task_cred(t), ns, cap);
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rcu_read_unlock();
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return (ret == 0);
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}
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/**
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* has_capability_noaudit - Does a task have a capability (unaudited) in the
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* initial user ns
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* @t: The task in question
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* @cap: The capability to be tested for
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*
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* Return true if the specified task has the given superior capability
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* currently in effect to init_user_ns, false if not. Don't write an
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* audit message for the check.
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*
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* Note that this does not set PF_SUPERPRIV on the task.
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*/
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bool has_capability_noaudit(struct task_struct *t, int cap)
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{
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return has_ns_capability_noaudit(t, &init_user_ns, cap);
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}
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/**
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* ns_capable - Determine if the current task has a superior capability in effect
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* @ns: The usernamespace we want the capability in
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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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bool ns_capable(struct user_namespace *ns, int cap)
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{
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if (unlikely(!cap_valid(cap))) {
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pr_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(current_cred(), ns, cap) == 0) {
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current->flags |= PF_SUPERPRIV;
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return true;
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}
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return false;
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}
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EXPORT_SYMBOL(ns_capable);
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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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bool capable(int cap)
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{
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return ns_capable(&init_user_ns, cap);
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}
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EXPORT_SYMBOL(capable);
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#endif /* CONFIG_MULTIUSER */
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/**
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* file_ns_capable - Determine if the file's opener had a capability in effect
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* @file: The file we want to check
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* @ns: The usernamespace we want the capability in
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* @cap: The capability to be tested for
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*
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* Return true if task that opened the file had a capability in effect
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* when the file was opened.
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*
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* This does not set PF_SUPERPRIV because the caller may not
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* actually be privileged.
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*/
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bool file_ns_capable(const struct file *file, struct user_namespace *ns,
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int cap)
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{
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if (WARN_ON_ONCE(!cap_valid(cap)))
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return false;
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if (security_capable(file->f_cred, ns, cap) == 0)
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return true;
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return false;
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}
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EXPORT_SYMBOL(file_ns_capable);
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/**
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* capable_wrt_inode_uidgid - Check nsown_capable and uid and gid mapped
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* @inode: The inode in question
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* @cap: The capability in question
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*
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* Return true if the current task has the given capability targeted at
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* its own user namespace and that the given inode's uid and gid are
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* mapped into the current user namespace.
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*/
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bool capable_wrt_inode_uidgid(const struct inode *inode, int cap)
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{
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struct user_namespace *ns = current_user_ns();
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return ns_capable(ns, cap) && kuid_has_mapping(ns, inode->i_uid) &&
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kgid_has_mapping(ns, inode->i_gid);
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}
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EXPORT_SYMBOL(capable_wrt_inode_uidgid);
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