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![Linus Torvalds](/assets/img/avatar_default.png)
Back in 2008 we extended the capability bits from 32 to 64, and we did it by extending the single 32-bit capability word from one word to an array of two words. It was then obfuscated by hiding the "2" behind two macro expansions, with the reasoning being that maybe it gets extended further some day. That reasoning may have been valid at the time, but the last thing we want to do is to extend the capability set any more. And the array of values not only causes source code oddities (with loops to deal with it), but also results in worse code generation. It's a lose-lose situation. So just change the 'u32[2]' into a 'u64' and be done with it. We still have to deal with the fact that the user space interface is designed around an array of these 32-bit values, but that was the case before too, since the array layouts were different (ie user space doesn't use an array of 32-bit values for individual capability masks, but an array of 32-bit slices of multiple masks). So that marshalling of data is actually simplified too, even if it does remain somewhat obscure and odd. This was all triggered by my reaction to the new "cap_isidentical()" introduced recently. By just using a saner data structure, it went from unsigned __capi; CAP_FOR_EACH_U32(__capi) { if (a.cap[__capi] != b.cap[__capi]) return false; } return true; to just being return a.val == b.val; instead. Which is rather more obvious both to humans and to compilers. Cc: Mateusz Guzik <mjguzik@gmail.com> Cc: Casey Schaufler <casey@schaufler-ca.com> Cc: Serge Hallyn <serge@hallyn.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Paul Moore <paul@paul-moore.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
521 lines
15 KiB
C
521 lines
15 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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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 <linux/uaccess.h>
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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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fallthrough; /* v3 is otherwise equivalent to v2 */
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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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struct __user_cap_data_struct kdata[2];
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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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return ret;
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/*
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* Annoying legacy format with 64-bit capabilities exposed
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* as two sets of 32-bit fields, so we need to split the
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* capability values up.
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*/
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kdata[0].effective = pE.val; kdata[1].effective = pE.val >> 32;
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kdata[0].permitted = pP.val; kdata[1].permitted = pP.val >> 32;
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kdata[0].inheritable = pI.val; kdata[1].inheritable = pI.val >> 32;
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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 * sizeof(kdata[0])))
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return -EFAULT;
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return 0;
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}
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static kernel_cap_t mk_kernel_cap(u32 low, u32 high)
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{
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return (kernel_cap_t) { (low | ((u64)high << 32)) & CAP_VALID_MASK };
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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[2] = { { 0, }, };
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unsigned 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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effective = mk_kernel_cap(kdata[0].effective, kdata[1].effective);
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permitted = mk_kernel_cap(kdata[0].permitted, kdata[1].permitted);
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inheritable = mk_kernel_cap(kdata[0].inheritable, kdata[1].inheritable);
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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, CAP_OPT_NONE);
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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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EXPORT_SYMBOL(has_capability);
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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(__task_cred(t), ns, cap, CAP_OPT_NOAUDIT);
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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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EXPORT_SYMBOL(has_capability_noaudit);
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static bool ns_capable_common(struct user_namespace *ns,
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int cap,
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unsigned int opts)
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{
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int capable;
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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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capable = security_capable(current_cred(), ns, cap, opts);
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if (capable == 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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/**
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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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return ns_capable_common(ns, cap, CAP_OPT_NONE);
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}
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EXPORT_SYMBOL(ns_capable);
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/**
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* ns_capable_noaudit - Determine if the current task has a superior capability
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* (unaudited) 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_noaudit(struct user_namespace *ns, int cap)
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{
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return ns_capable_common(ns, cap, CAP_OPT_NOAUDIT);
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}
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EXPORT_SYMBOL(ns_capable_noaudit);
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/**
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* ns_capable_setid - Determine if the current task has a superior capability
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* in effect, while signalling that this check is being done from within a
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* setid or setgroups syscall.
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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_setid(struct user_namespace *ns, int cap)
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{
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return ns_capable_common(ns, cap, CAP_OPT_INSETID);
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}
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EXPORT_SYMBOL(ns_capable_setid);
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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, CAP_OPT_NONE) == 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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* privileged_wrt_inode_uidgid - Do capabilities in the namespace work over the inode?
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* @ns: The user namespace in question
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* @inode: The inode in question
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*
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* Return true if the inode uid and gid are within the namespace.
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*/
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bool privileged_wrt_inode_uidgid(struct user_namespace *ns,
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struct mnt_idmap *idmap,
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const struct inode *inode)
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{
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return vfsuid_has_mapping(ns, i_uid_into_vfsuid(idmap, inode)) &&
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vfsgid_has_mapping(ns, i_gid_into_vfsgid(idmap, inode));
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}
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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
|
|
* mapped into the current user namespace.
|
|
*/
|
|
bool capable_wrt_inode_uidgid(struct mnt_idmap *idmap,
|
|
const struct inode *inode, int cap)
|
|
{
|
|
struct user_namespace *ns = current_user_ns();
|
|
|
|
return ns_capable(ns, cap) &&
|
|
privileged_wrt_inode_uidgid(ns, idmap, inode);
|
|
}
|
|
EXPORT_SYMBOL(capable_wrt_inode_uidgid);
|
|
|
|
/**
|
|
* ptracer_capable - Determine if the ptracer holds CAP_SYS_PTRACE in the namespace
|
|
* @tsk: The task that may be ptraced
|
|
* @ns: The user namespace to search for CAP_SYS_PTRACE in
|
|
*
|
|
* Return true if the task that is ptracing the current task had CAP_SYS_PTRACE
|
|
* in the specified user namespace.
|
|
*/
|
|
bool ptracer_capable(struct task_struct *tsk, struct user_namespace *ns)
|
|
{
|
|
int ret = 0; /* An absent tracer adds no restrictions */
|
|
const struct cred *cred;
|
|
|
|
rcu_read_lock();
|
|
cred = rcu_dereference(tsk->ptracer_cred);
|
|
if (cred)
|
|
ret = security_capable(cred, ns, CAP_SYS_PTRACE,
|
|
CAP_OPT_NOAUDIT);
|
|
rcu_read_unlock();
|
|
return (ret == 0);
|
|
}
|