forked from Qortal/Brooklyn
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
451 lines
13 KiB
451 lines
13 KiB
// SPDX-License-Identifier: GPL-2.0-only |
|
/* |
|
* Landlock LSM - System call implementations and user space interfaces |
|
* |
|
* Copyright © 2016-2020 Mickaël Salaün <[email protected]> |
|
* Copyright © 2018-2020 ANSSI |
|
*/ |
|
|
|
#include <asm/current.h> |
|
#include <linux/anon_inodes.h> |
|
#include <linux/build_bug.h> |
|
#include <linux/capability.h> |
|
#include <linux/compiler_types.h> |
|
#include <linux/dcache.h> |
|
#include <linux/err.h> |
|
#include <linux/errno.h> |
|
#include <linux/fs.h> |
|
#include <linux/limits.h> |
|
#include <linux/mount.h> |
|
#include <linux/path.h> |
|
#include <linux/sched.h> |
|
#include <linux/security.h> |
|
#include <linux/stddef.h> |
|
#include <linux/syscalls.h> |
|
#include <linux/types.h> |
|
#include <linux/uaccess.h> |
|
#include <uapi/linux/landlock.h> |
|
|
|
#include "cred.h" |
|
#include "fs.h" |
|
#include "limits.h" |
|
#include "ruleset.h" |
|
#include "setup.h" |
|
|
|
/** |
|
* copy_min_struct_from_user - Safe future-proof argument copying |
|
* |
|
* Extend copy_struct_from_user() to check for consistent user buffer. |
|
* |
|
* @dst: Kernel space pointer or NULL. |
|
* @ksize: Actual size of the data pointed to by @dst. |
|
* @ksize_min: Minimal required size to be copied. |
|
* @src: User space pointer or NULL. |
|
* @usize: (Alleged) size of the data pointed to by @src. |
|
*/ |
|
static __always_inline int copy_min_struct_from_user(void *const dst, |
|
const size_t ksize, const size_t ksize_min, |
|
const void __user *const src, const size_t usize) |
|
{ |
|
/* Checks buffer inconsistencies. */ |
|
BUILD_BUG_ON(!dst); |
|
if (!src) |
|
return -EFAULT; |
|
|
|
/* Checks size ranges. */ |
|
BUILD_BUG_ON(ksize <= 0); |
|
BUILD_BUG_ON(ksize < ksize_min); |
|
if (usize < ksize_min) |
|
return -EINVAL; |
|
if (usize > PAGE_SIZE) |
|
return -E2BIG; |
|
|
|
/* Copies user buffer and fills with zeros. */ |
|
return copy_struct_from_user(dst, ksize, src, usize); |
|
} |
|
|
|
/* |
|
* This function only contains arithmetic operations with constants, leading to |
|
* BUILD_BUG_ON(). The related code is evaluated and checked at build time, |
|
* but it is then ignored thanks to compiler optimizations. |
|
*/ |
|
static void build_check_abi(void) |
|
{ |
|
struct landlock_ruleset_attr ruleset_attr; |
|
struct landlock_path_beneath_attr path_beneath_attr; |
|
size_t ruleset_size, path_beneath_size; |
|
|
|
/* |
|
* For each user space ABI structures, first checks that there is no |
|
* hole in them, then checks that all architectures have the same |
|
* struct size. |
|
*/ |
|
ruleset_size = sizeof(ruleset_attr.handled_access_fs); |
|
BUILD_BUG_ON(sizeof(ruleset_attr) != ruleset_size); |
|
BUILD_BUG_ON(sizeof(ruleset_attr) != 8); |
|
|
|
path_beneath_size = sizeof(path_beneath_attr.allowed_access); |
|
path_beneath_size += sizeof(path_beneath_attr.parent_fd); |
|
BUILD_BUG_ON(sizeof(path_beneath_attr) != path_beneath_size); |
|
BUILD_BUG_ON(sizeof(path_beneath_attr) != 12); |
|
} |
|
|
|
/* Ruleset handling */ |
|
|
|
static int fop_ruleset_release(struct inode *const inode, |
|
struct file *const filp) |
|
{ |
|
struct landlock_ruleset *ruleset = filp->private_data; |
|
|
|
landlock_put_ruleset(ruleset); |
|
return 0; |
|
} |
|
|
|
static ssize_t fop_dummy_read(struct file *const filp, char __user *const buf, |
|
const size_t size, loff_t *const ppos) |
|
{ |
|
/* Dummy handler to enable FMODE_CAN_READ. */ |
|
return -EINVAL; |
|
} |
|
|
|
static ssize_t fop_dummy_write(struct file *const filp, |
|
const char __user *const buf, const size_t size, |
|
loff_t *const ppos) |
|
{ |
|
/* Dummy handler to enable FMODE_CAN_WRITE. */ |
|
return -EINVAL; |
|
} |
|
|
|
/* |
|
* A ruleset file descriptor enables to build a ruleset by adding (i.e. |
|
* writing) rule after rule, without relying on the task's context. This |
|
* reentrant design is also used in a read way to enforce the ruleset on the |
|
* current task. |
|
*/ |
|
static const struct file_operations ruleset_fops = { |
|
.release = fop_ruleset_release, |
|
.read = fop_dummy_read, |
|
.write = fop_dummy_write, |
|
}; |
|
|
|
#define LANDLOCK_ABI_VERSION 1 |
|
|
|
/** |
|
* sys_landlock_create_ruleset - Create a new ruleset |
|
* |
|
* @attr: Pointer to a &struct landlock_ruleset_attr identifying the scope of |
|
* the new ruleset. |
|
* @size: Size of the pointed &struct landlock_ruleset_attr (needed for |
|
* backward and forward compatibility). |
|
* @flags: Supported value: %LANDLOCK_CREATE_RULESET_VERSION. |
|
* |
|
* This system call enables to create a new Landlock ruleset, and returns the |
|
* related file descriptor on success. |
|
* |
|
* If @flags is %LANDLOCK_CREATE_RULESET_VERSION and @attr is NULL and @size is |
|
* 0, then the returned value is the highest supported Landlock ABI version |
|
* (starting at 1). |
|
* |
|
* Possible returned errors are: |
|
* |
|
* - EOPNOTSUPP: Landlock is supported by the kernel but disabled at boot time; |
|
* - EINVAL: unknown @flags, or unknown access, or too small @size; |
|
* - E2BIG or EFAULT: @attr or @size inconsistencies; |
|
* - ENOMSG: empty &landlock_ruleset_attr.handled_access_fs. |
|
*/ |
|
SYSCALL_DEFINE3(landlock_create_ruleset, |
|
const struct landlock_ruleset_attr __user *const, attr, |
|
const size_t, size, const __u32, flags) |
|
{ |
|
struct landlock_ruleset_attr ruleset_attr; |
|
struct landlock_ruleset *ruleset; |
|
int err, ruleset_fd; |
|
|
|
/* Build-time checks. */ |
|
build_check_abi(); |
|
|
|
if (!landlock_initialized) |
|
return -EOPNOTSUPP; |
|
|
|
if (flags) { |
|
if ((flags == LANDLOCK_CREATE_RULESET_VERSION) |
|
&& !attr && !size) |
|
return LANDLOCK_ABI_VERSION; |
|
return -EINVAL; |
|
} |
|
|
|
/* Copies raw user space buffer. */ |
|
err = copy_min_struct_from_user(&ruleset_attr, sizeof(ruleset_attr), |
|
offsetofend(typeof(ruleset_attr), handled_access_fs), |
|
attr, size); |
|
if (err) |
|
return err; |
|
|
|
/* Checks content (and 32-bits cast). */ |
|
if ((ruleset_attr.handled_access_fs | LANDLOCK_MASK_ACCESS_FS) != |
|
LANDLOCK_MASK_ACCESS_FS) |
|
return -EINVAL; |
|
|
|
/* Checks arguments and transforms to kernel struct. */ |
|
ruleset = landlock_create_ruleset(ruleset_attr.handled_access_fs); |
|
if (IS_ERR(ruleset)) |
|
return PTR_ERR(ruleset); |
|
|
|
/* Creates anonymous FD referring to the ruleset. */ |
|
ruleset_fd = anon_inode_getfd("[landlock-ruleset]", &ruleset_fops, |
|
ruleset, O_RDWR | O_CLOEXEC); |
|
if (ruleset_fd < 0) |
|
landlock_put_ruleset(ruleset); |
|
return ruleset_fd; |
|
} |
|
|
|
/* |
|
* Returns an owned ruleset from a FD. It is thus needed to call |
|
* landlock_put_ruleset() on the return value. |
|
*/ |
|
static struct landlock_ruleset *get_ruleset_from_fd(const int fd, |
|
const fmode_t mode) |
|
{ |
|
struct fd ruleset_f; |
|
struct landlock_ruleset *ruleset; |
|
|
|
ruleset_f = fdget(fd); |
|
if (!ruleset_f.file) |
|
return ERR_PTR(-EBADF); |
|
|
|
/* Checks FD type and access right. */ |
|
if (ruleset_f.file->f_op != &ruleset_fops) { |
|
ruleset = ERR_PTR(-EBADFD); |
|
goto out_fdput; |
|
} |
|
if (!(ruleset_f.file->f_mode & mode)) { |
|
ruleset = ERR_PTR(-EPERM); |
|
goto out_fdput; |
|
} |
|
ruleset = ruleset_f.file->private_data; |
|
if (WARN_ON_ONCE(ruleset->num_layers != 1)) { |
|
ruleset = ERR_PTR(-EINVAL); |
|
goto out_fdput; |
|
} |
|
landlock_get_ruleset(ruleset); |
|
|
|
out_fdput: |
|
fdput(ruleset_f); |
|
return ruleset; |
|
} |
|
|
|
/* Path handling */ |
|
|
|
/* |
|
* @path: Must call put_path(@path) after the call if it succeeded. |
|
*/ |
|
static int get_path_from_fd(const s32 fd, struct path *const path) |
|
{ |
|
struct fd f; |
|
int err = 0; |
|
|
|
BUILD_BUG_ON(!__same_type(fd, |
|
((struct landlock_path_beneath_attr *)NULL)->parent_fd)); |
|
|
|
/* Handles O_PATH. */ |
|
f = fdget_raw(fd); |
|
if (!f.file) |
|
return -EBADF; |
|
/* |
|
* Forbids ruleset FDs, internal filesystems (e.g. nsfs), including |
|
* pseudo filesystems that will never be mountable (e.g. sockfs, |
|
* pipefs). |
|
*/ |
|
if ((f.file->f_op == &ruleset_fops) || |
|
(f.file->f_path.mnt->mnt_flags & MNT_INTERNAL) || |
|
(f.file->f_path.dentry->d_sb->s_flags & SB_NOUSER) || |
|
d_is_negative(f.file->f_path.dentry) || |
|
IS_PRIVATE(d_backing_inode(f.file->f_path.dentry))) { |
|
err = -EBADFD; |
|
goto out_fdput; |
|
} |
|
*path = f.file->f_path; |
|
path_get(path); |
|
|
|
out_fdput: |
|
fdput(f); |
|
return err; |
|
} |
|
|
|
/** |
|
* sys_landlock_add_rule - Add a new rule to a ruleset |
|
* |
|
* @ruleset_fd: File descriptor tied to the ruleset that should be extended |
|
* with the new rule. |
|
* @rule_type: Identify the structure type pointed to by @rule_attr (only |
|
* LANDLOCK_RULE_PATH_BENEATH for now). |
|
* @rule_attr: Pointer to a rule (only of type &struct |
|
* landlock_path_beneath_attr for now). |
|
* @flags: Must be 0. |
|
* |
|
* This system call enables to define a new rule and add it to an existing |
|
* ruleset. |
|
* |
|
* Possible returned errors are: |
|
* |
|
* - EOPNOTSUPP: Landlock is supported by the kernel but disabled at boot time; |
|
* - EINVAL: @flags is not 0, or inconsistent access in the rule (i.e. |
|
* &landlock_path_beneath_attr.allowed_access is not a subset of the rule's |
|
* accesses); |
|
* - ENOMSG: Empty accesses (e.g. &landlock_path_beneath_attr.allowed_access); |
|
* - EBADF: @ruleset_fd is not a file descriptor for the current thread, or a |
|
* member of @rule_attr is not a file descriptor as expected; |
|
* - EBADFD: @ruleset_fd is not a ruleset file descriptor, or a member of |
|
* @rule_attr is not the expected file descriptor type (e.g. file open |
|
* without O_PATH); |
|
* - EPERM: @ruleset_fd has no write access to the underlying ruleset; |
|
* - EFAULT: @rule_attr inconsistency. |
|
*/ |
|
SYSCALL_DEFINE4(landlock_add_rule, |
|
const int, ruleset_fd, const enum landlock_rule_type, rule_type, |
|
const void __user *const, rule_attr, const __u32, flags) |
|
{ |
|
struct landlock_path_beneath_attr path_beneath_attr; |
|
struct path path; |
|
struct landlock_ruleset *ruleset; |
|
int res, err; |
|
|
|
if (!landlock_initialized) |
|
return -EOPNOTSUPP; |
|
|
|
/* No flag for now. */ |
|
if (flags) |
|
return -EINVAL; |
|
|
|
if (rule_type != LANDLOCK_RULE_PATH_BENEATH) |
|
return -EINVAL; |
|
|
|
/* Copies raw user space buffer, only one type for now. */ |
|
res = copy_from_user(&path_beneath_attr, rule_attr, |
|
sizeof(path_beneath_attr)); |
|
if (res) |
|
return -EFAULT; |
|
|
|
/* Gets and checks the ruleset. */ |
|
ruleset = get_ruleset_from_fd(ruleset_fd, FMODE_CAN_WRITE); |
|
if (IS_ERR(ruleset)) |
|
return PTR_ERR(ruleset); |
|
|
|
/* |
|
* Informs about useless rule: empty allowed_access (i.e. deny rules) |
|
* are ignored in path walks. |
|
*/ |
|
if (!path_beneath_attr.allowed_access) { |
|
err = -ENOMSG; |
|
goto out_put_ruleset; |
|
} |
|
/* |
|
* Checks that allowed_access matches the @ruleset constraints |
|
* (ruleset->fs_access_masks[0] is automatically upgraded to 64-bits). |
|
*/ |
|
if ((path_beneath_attr.allowed_access | ruleset->fs_access_masks[0]) != |
|
ruleset->fs_access_masks[0]) { |
|
err = -EINVAL; |
|
goto out_put_ruleset; |
|
} |
|
|
|
/* Gets and checks the new rule. */ |
|
err = get_path_from_fd(path_beneath_attr.parent_fd, &path); |
|
if (err) |
|
goto out_put_ruleset; |
|
|
|
/* Imports the new rule. */ |
|
err = landlock_append_fs_rule(ruleset, &path, |
|
path_beneath_attr.allowed_access); |
|
path_put(&path); |
|
|
|
out_put_ruleset: |
|
landlock_put_ruleset(ruleset); |
|
return err; |
|
} |
|
|
|
/* Enforcement */ |
|
|
|
/** |
|
* sys_landlock_restrict_self - Enforce a ruleset on the calling thread |
|
* |
|
* @ruleset_fd: File descriptor tied to the ruleset to merge with the target. |
|
* @flags: Must be 0. |
|
* |
|
* This system call enables to enforce a Landlock ruleset on the current |
|
* thread. Enforcing a ruleset requires that the task has CAP_SYS_ADMIN in its |
|
* namespace or is running with no_new_privs. This avoids scenarios where |
|
* unprivileged tasks can affect the behavior of privileged children. |
|
* |
|
* Possible returned errors are: |
|
* |
|
* - EOPNOTSUPP: Landlock is supported by the kernel but disabled at boot time; |
|
* - EINVAL: @flags is not 0. |
|
* - EBADF: @ruleset_fd is not a file descriptor for the current thread; |
|
* - EBADFD: @ruleset_fd is not a ruleset file descriptor; |
|
* - EPERM: @ruleset_fd has no read access to the underlying ruleset, or the |
|
* current thread is not running with no_new_privs, or it doesn't have |
|
* CAP_SYS_ADMIN in its namespace. |
|
* - E2BIG: The maximum number of stacked rulesets is reached for the current |
|
* thread. |
|
*/ |
|
SYSCALL_DEFINE2(landlock_restrict_self, |
|
const int, ruleset_fd, const __u32, flags) |
|
{ |
|
struct landlock_ruleset *new_dom, *ruleset; |
|
struct cred *new_cred; |
|
struct landlock_cred_security *new_llcred; |
|
int err; |
|
|
|
if (!landlock_initialized) |
|
return -EOPNOTSUPP; |
|
|
|
/* No flag for now. */ |
|
if (flags) |
|
return -EINVAL; |
|
|
|
/* |
|
* Similar checks as for seccomp(2), except that an -EPERM may be |
|
* returned. |
|
*/ |
|
if (!task_no_new_privs(current) && |
|
!ns_capable_noaudit(current_user_ns(), CAP_SYS_ADMIN)) |
|
return -EPERM; |
|
|
|
/* Gets and checks the ruleset. */ |
|
ruleset = get_ruleset_from_fd(ruleset_fd, FMODE_CAN_READ); |
|
if (IS_ERR(ruleset)) |
|
return PTR_ERR(ruleset); |
|
|
|
/* Prepares new credentials. */ |
|
new_cred = prepare_creds(); |
|
if (!new_cred) { |
|
err = -ENOMEM; |
|
goto out_put_ruleset; |
|
} |
|
new_llcred = landlock_cred(new_cred); |
|
|
|
/* |
|
* There is no possible race condition while copying and manipulating |
|
* the current credentials because they are dedicated per thread. |
|
*/ |
|
new_dom = landlock_merge_ruleset(new_llcred->domain, ruleset); |
|
if (IS_ERR(new_dom)) { |
|
err = PTR_ERR(new_dom); |
|
goto out_put_creds; |
|
} |
|
|
|
/* Replaces the old (prepared) domain. */ |
|
landlock_put_ruleset(new_llcred->domain); |
|
new_llcred->domain = new_dom; |
|
|
|
landlock_put_ruleset(ruleset); |
|
return commit_creds(new_cred); |
|
|
|
out_put_creds: |
|
abort_creds(new_cred); |
|
|
|
out_put_ruleset: |
|
landlock_put_ruleset(ruleset); |
|
return err; |
|
}
|
|
|