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linux-stable/security/landlock/setup.c

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landlock: Set up the security framework and manage credentials Process's credentials point to a Landlock domain, which is underneath implemented with a ruleset. In the following commits, this domain is used to check and enforce the ptrace and filesystem security policies. A domain is inherited from a parent to its child the same way a thread inherits a seccomp policy. Cc: James Morris <jmorris@namei.org> Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com> Reviewed-by: Jann Horn <jannh@google.com> Acked-by: Serge Hallyn <serge@hallyn.com> Reviewed-by: Kees Cook <keescook@chromium.org> Link: https://lore.kernel.org/r/20210422154123.13086-4-mic@digikod.net Signed-off-by: James Morris <jamorris@linux.microsoft.com>
2021-04-22 15:41:13 +00:00
// SPDX-License-Identifier: GPL-2.0-only
/*
* Landlock LSM - Security framework setup
*
* Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net>
* Copyright © 2018-2020 ANSSI
*/
#include <linux/init.h>
#include <linux/lsm_hooks.h>
#include "common.h"
#include "cred.h"
landlock: Support filesystem access-control Using Landlock objects and ruleset, it is possible to tag inodes according to a process's domain. To enable an unprivileged process to express a file hierarchy, it first needs to open a directory (or a file) and pass this file descriptor to the kernel through landlock_add_rule(2). When checking if a file access request is allowed, we walk from the requested dentry to the real root, following the different mount layers. The access to each "tagged" inodes are collected according to their rule layer level, and ANDed to create access to the requested file hierarchy. This makes possible to identify a lot of files without tagging every inodes nor modifying the filesystem, while still following the view and understanding the user has from the filesystem. Add a new ARCH_EPHEMERAL_INODES for UML because it currently does not keep the same struct inodes for the same inodes whereas these inodes are in use. This commit adds a minimal set of supported filesystem access-control which doesn't enable to restrict all file-related actions. This is the result of multiple discussions to minimize the code of Landlock to ease review. Thanks to the Landlock design, extending this access-control without breaking user space will not be a problem. Moreover, seccomp filters can be used to restrict the use of syscall families which may not be currently handled by Landlock. Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Anton Ivanov <anton.ivanov@cambridgegreys.com> Cc: James Morris <jmorris@namei.org> Cc: Jann Horn <jannh@google.com> Cc: Jeff Dike <jdike@addtoit.com> Cc: Kees Cook <keescook@chromium.org> Cc: Richard Weinberger <richard@nod.at> Cc: Serge E. Hallyn <serge@hallyn.com> Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com> Link: https://lore.kernel.org/r/20210422154123.13086-8-mic@digikod.net Signed-off-by: James Morris <jamorris@linux.microsoft.com>
2021-04-22 15:41:17 +00:00
#include "fs.h"
landlock: Add ptrace restrictions Using ptrace(2) and related debug features on a target process can lead to a privilege escalation. Indeed, ptrace(2) can be used by an attacker to impersonate another task and to remain undetected while performing malicious activities. Thanks to ptrace_may_access(), various part of the kernel can check if a tracer is more privileged than a tracee. A landlocked process has fewer privileges than a non-landlocked process and must then be subject to additional restrictions when manipulating processes. To be allowed to use ptrace(2) and related syscalls on a target process, a landlocked process must have a subset of the target process's rules (i.e. the tracee must be in a sub-domain of the tracer). Cc: James Morris <jmorris@namei.org> Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com> Reviewed-by: Jann Horn <jannh@google.com> Acked-by: Serge Hallyn <serge@hallyn.com> Reviewed-by: Kees Cook <keescook@chromium.org> Link: https://lore.kernel.org/r/20210422154123.13086-5-mic@digikod.net Signed-off-by: James Morris <jamorris@linux.microsoft.com>
2021-04-22 15:41:14 +00:00
#include "ptrace.h"
landlock: Set up the security framework and manage credentials Process's credentials point to a Landlock domain, which is underneath implemented with a ruleset. In the following commits, this domain is used to check and enforce the ptrace and filesystem security policies. A domain is inherited from a parent to its child the same way a thread inherits a seccomp policy. Cc: James Morris <jmorris@namei.org> Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com> Reviewed-by: Jann Horn <jannh@google.com> Acked-by: Serge Hallyn <serge@hallyn.com> Reviewed-by: Kees Cook <keescook@chromium.org> Link: https://lore.kernel.org/r/20210422154123.13086-4-mic@digikod.net Signed-off-by: James Morris <jamorris@linux.microsoft.com>
2021-04-22 15:41:13 +00:00
#include "setup.h"
selinux: remove the runtime disable functionality After working with the larger SELinux-based distros for several years, we're finally at a place where we can disable the SELinux runtime disable functionality. The existing kernel deprecation notice explains the functionality and why we want to remove it: The selinuxfs "disable" node allows SELinux to be disabled at runtime prior to a policy being loaded into the kernel. If disabled via this mechanism, SELinux will remain disabled until the system is rebooted. The preferred method of disabling SELinux is via the "selinux=0" boot parameter, but the selinuxfs "disable" node was created to make it easier for systems with primitive bootloaders that did not allow for easy modification of the kernel command line. Unfortunately, allowing for SELinux to be disabled at runtime makes it difficult to secure the kernel's LSM hooks using the "__ro_after_init" feature. It is that last sentence, mentioning the '__ro_after_init' hardening, which is the real motivation for this change, and if you look at the diffstat you'll see that the impact of this patch reaches across all the different LSMs, helping prevent tampering at the LSM hook level. From a SELinux perspective, it is important to note that if you continue to disable SELinux via "/etc/selinux/config" it may appear that SELinux is disabled, but it is simply in an uninitialized state. If you load a policy with `load_policy -i`, you will see SELinux come alive just as if you had loaded the policy during early-boot. It is also worth noting that the "/sys/fs/selinux/disable" file is always writable now, regardless of the Kconfig settings, but writing to the file has no effect on the system, other than to display an error on the console if a non-zero/true value is written. Finally, in the several years where we have been working on deprecating this functionality, there has only been one instance of someone mentioning any user visible breakage. In this particular case it was an individual's kernel test system, and the workaround documented in the deprecation notice ("selinux=0" on the kernel command line) resolved the issue without problem. Acked-by: Casey Schaufler <casey@schaufler-ca.com> Signed-off-by: Paul Moore <paul@paul-moore.com>
2023-03-17 16:43:07 +00:00
bool landlock_initialized __ro_after_init = false;
landlock: Support filesystem access-control Using Landlock objects and ruleset, it is possible to tag inodes according to a process's domain. To enable an unprivileged process to express a file hierarchy, it first needs to open a directory (or a file) and pass this file descriptor to the kernel through landlock_add_rule(2). When checking if a file access request is allowed, we walk from the requested dentry to the real root, following the different mount layers. The access to each "tagged" inodes are collected according to their rule layer level, and ANDed to create access to the requested file hierarchy. This makes possible to identify a lot of files without tagging every inodes nor modifying the filesystem, while still following the view and understanding the user has from the filesystem. Add a new ARCH_EPHEMERAL_INODES for UML because it currently does not keep the same struct inodes for the same inodes whereas these inodes are in use. This commit adds a minimal set of supported filesystem access-control which doesn't enable to restrict all file-related actions. This is the result of multiple discussions to minimize the code of Landlock to ease review. Thanks to the Landlock design, extending this access-control without breaking user space will not be a problem. Moreover, seccomp filters can be used to restrict the use of syscall families which may not be currently handled by Landlock. Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Anton Ivanov <anton.ivanov@cambridgegreys.com> Cc: James Morris <jmorris@namei.org> Cc: Jann Horn <jannh@google.com> Cc: Jeff Dike <jdike@addtoit.com> Cc: Kees Cook <keescook@chromium.org> Cc: Richard Weinberger <richard@nod.at> Cc: Serge E. Hallyn <serge@hallyn.com> Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com> Link: https://lore.kernel.org/r/20210422154123.13086-8-mic@digikod.net Signed-off-by: James Morris <jamorris@linux.microsoft.com>
2021-04-22 15:41:17 +00:00
selinux: remove the runtime disable functionality After working with the larger SELinux-based distros for several years, we're finally at a place where we can disable the SELinux runtime disable functionality. The existing kernel deprecation notice explains the functionality and why we want to remove it: The selinuxfs "disable" node allows SELinux to be disabled at runtime prior to a policy being loaded into the kernel. If disabled via this mechanism, SELinux will remain disabled until the system is rebooted. The preferred method of disabling SELinux is via the "selinux=0" boot parameter, but the selinuxfs "disable" node was created to make it easier for systems with primitive bootloaders that did not allow for easy modification of the kernel command line. Unfortunately, allowing for SELinux to be disabled at runtime makes it difficult to secure the kernel's LSM hooks using the "__ro_after_init" feature. It is that last sentence, mentioning the '__ro_after_init' hardening, which is the real motivation for this change, and if you look at the diffstat you'll see that the impact of this patch reaches across all the different LSMs, helping prevent tampering at the LSM hook level. From a SELinux perspective, it is important to note that if you continue to disable SELinux via "/etc/selinux/config" it may appear that SELinux is disabled, but it is simply in an uninitialized state. If you load a policy with `load_policy -i`, you will see SELinux come alive just as if you had loaded the policy during early-boot. It is also worth noting that the "/sys/fs/selinux/disable" file is always writable now, regardless of the Kconfig settings, but writing to the file has no effect on the system, other than to display an error on the console if a non-zero/true value is written. Finally, in the several years where we have been working on deprecating this functionality, there has only been one instance of someone mentioning any user visible breakage. In this particular case it was an individual's kernel test system, and the workaround documented in the deprecation notice ("selinux=0" on the kernel command line) resolved the issue without problem. Acked-by: Casey Schaufler <casey@schaufler-ca.com> Signed-off-by: Paul Moore <paul@paul-moore.com>
2023-03-17 16:43:07 +00:00
struct lsm_blob_sizes landlock_blob_sizes __ro_after_init = {
landlock: Set up the security framework and manage credentials Process's credentials point to a Landlock domain, which is underneath implemented with a ruleset. In the following commits, this domain is used to check and enforce the ptrace and filesystem security policies. A domain is inherited from a parent to its child the same way a thread inherits a seccomp policy. Cc: James Morris <jmorris@namei.org> Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com> Reviewed-by: Jann Horn <jannh@google.com> Acked-by: Serge Hallyn <serge@hallyn.com> Reviewed-by: Kees Cook <keescook@chromium.org> Link: https://lore.kernel.org/r/20210422154123.13086-4-mic@digikod.net Signed-off-by: James Morris <jamorris@linux.microsoft.com>
2021-04-22 15:41:13 +00:00
.lbs_cred = sizeof(struct landlock_cred_security),
landlock: Support file truncation Introduce the LANDLOCK_ACCESS_FS_TRUNCATE flag for file truncation. This flag hooks into the path_truncate, file_truncate and file_alloc_security LSM hooks and covers file truncation using truncate(2), ftruncate(2), open(2) with O_TRUNC, as well as creat(). This change also increments the Landlock ABI version, updates corresponding selftests, and updates code documentation to document the flag. In security/security.c, allocate security blobs at pointer-aligned offsets. This fixes the problem where one LSM's security blob can shift another LSM's security blob to an unaligned address (reported by Nathan Chancellor). The following operations are restricted: open(2): requires the LANDLOCK_ACCESS_FS_TRUNCATE right if a file gets implicitly truncated as part of the open() (e.g. using O_TRUNC). Notable special cases: * open(..., O_RDONLY|O_TRUNC) can truncate files as well in Linux * open() with O_TRUNC does *not* need the TRUNCATE right when it creates a new file. truncate(2) (on a path): requires the LANDLOCK_ACCESS_FS_TRUNCATE right. ftruncate(2) (on a file): requires that the file had the TRUNCATE right when it was previously opened. File descriptors acquired by other means than open(2) (e.g. memfd_create(2)) continue to support truncation with ftruncate(2). Cc: Nathan Chancellor <nathan@kernel.org> Signed-off-by: Günther Noack <gnoack3000@gmail.com> Acked-by: Paul Moore <paul@paul-moore.com> (LSM) Link: https://lore.kernel.org/r/20221018182216.301684-5-gnoack3000@gmail.com Signed-off-by: Mickaël Salaün <mic@digikod.net>
2022-10-18 18:22:09 +00:00
.lbs_file = sizeof(struct landlock_file_security),
landlock: Support filesystem access-control Using Landlock objects and ruleset, it is possible to tag inodes according to a process's domain. To enable an unprivileged process to express a file hierarchy, it first needs to open a directory (or a file) and pass this file descriptor to the kernel through landlock_add_rule(2). When checking if a file access request is allowed, we walk from the requested dentry to the real root, following the different mount layers. The access to each "tagged" inodes are collected according to their rule layer level, and ANDed to create access to the requested file hierarchy. This makes possible to identify a lot of files without tagging every inodes nor modifying the filesystem, while still following the view and understanding the user has from the filesystem. Add a new ARCH_EPHEMERAL_INODES for UML because it currently does not keep the same struct inodes for the same inodes whereas these inodes are in use. This commit adds a minimal set of supported filesystem access-control which doesn't enable to restrict all file-related actions. This is the result of multiple discussions to minimize the code of Landlock to ease review. Thanks to the Landlock design, extending this access-control without breaking user space will not be a problem. Moreover, seccomp filters can be used to restrict the use of syscall families which may not be currently handled by Landlock. Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Anton Ivanov <anton.ivanov@cambridgegreys.com> Cc: James Morris <jmorris@namei.org> Cc: Jann Horn <jannh@google.com> Cc: Jeff Dike <jdike@addtoit.com> Cc: Kees Cook <keescook@chromium.org> Cc: Richard Weinberger <richard@nod.at> Cc: Serge E. Hallyn <serge@hallyn.com> Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com> Link: https://lore.kernel.org/r/20210422154123.13086-8-mic@digikod.net Signed-off-by: James Morris <jamorris@linux.microsoft.com>
2021-04-22 15:41:17 +00:00
.lbs_inode = sizeof(struct landlock_inode_security),
.lbs_superblock = sizeof(struct landlock_superblock_security),
landlock: Set up the security framework and manage credentials Process's credentials point to a Landlock domain, which is underneath implemented with a ruleset. In the following commits, this domain is used to check and enforce the ptrace and filesystem security policies. A domain is inherited from a parent to its child the same way a thread inherits a seccomp policy. Cc: James Morris <jmorris@namei.org> Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com> Reviewed-by: Jann Horn <jannh@google.com> Acked-by: Serge Hallyn <serge@hallyn.com> Reviewed-by: Kees Cook <keescook@chromium.org> Link: https://lore.kernel.org/r/20210422154123.13086-4-mic@digikod.net Signed-off-by: James Morris <jamorris@linux.microsoft.com>
2021-04-22 15:41:13 +00:00
};
static int __init landlock_init(void)
{
landlock_add_cred_hooks();
landlock: Add ptrace restrictions Using ptrace(2) and related debug features on a target process can lead to a privilege escalation. Indeed, ptrace(2) can be used by an attacker to impersonate another task and to remain undetected while performing malicious activities. Thanks to ptrace_may_access(), various part of the kernel can check if a tracer is more privileged than a tracee. A landlocked process has fewer privileges than a non-landlocked process and must then be subject to additional restrictions when manipulating processes. To be allowed to use ptrace(2) and related syscalls on a target process, a landlocked process must have a subset of the target process's rules (i.e. the tracee must be in a sub-domain of the tracer). Cc: James Morris <jmorris@namei.org> Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com> Reviewed-by: Jann Horn <jannh@google.com> Acked-by: Serge Hallyn <serge@hallyn.com> Reviewed-by: Kees Cook <keescook@chromium.org> Link: https://lore.kernel.org/r/20210422154123.13086-5-mic@digikod.net Signed-off-by: James Morris <jamorris@linux.microsoft.com>
2021-04-22 15:41:14 +00:00
landlock_add_ptrace_hooks();
landlock: Support filesystem access-control Using Landlock objects and ruleset, it is possible to tag inodes according to a process's domain. To enable an unprivileged process to express a file hierarchy, it first needs to open a directory (or a file) and pass this file descriptor to the kernel through landlock_add_rule(2). When checking if a file access request is allowed, we walk from the requested dentry to the real root, following the different mount layers. The access to each "tagged" inodes are collected according to their rule layer level, and ANDed to create access to the requested file hierarchy. This makes possible to identify a lot of files without tagging every inodes nor modifying the filesystem, while still following the view and understanding the user has from the filesystem. Add a new ARCH_EPHEMERAL_INODES for UML because it currently does not keep the same struct inodes for the same inodes whereas these inodes are in use. This commit adds a minimal set of supported filesystem access-control which doesn't enable to restrict all file-related actions. This is the result of multiple discussions to minimize the code of Landlock to ease review. Thanks to the Landlock design, extending this access-control without breaking user space will not be a problem. Moreover, seccomp filters can be used to restrict the use of syscall families which may not be currently handled by Landlock. Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Anton Ivanov <anton.ivanov@cambridgegreys.com> Cc: James Morris <jmorris@namei.org> Cc: Jann Horn <jannh@google.com> Cc: Jeff Dike <jdike@addtoit.com> Cc: Kees Cook <keescook@chromium.org> Cc: Richard Weinberger <richard@nod.at> Cc: Serge E. Hallyn <serge@hallyn.com> Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com> Link: https://lore.kernel.org/r/20210422154123.13086-8-mic@digikod.net Signed-off-by: James Morris <jamorris@linux.microsoft.com>
2021-04-22 15:41:17 +00:00
landlock_add_fs_hooks();
landlock_initialized = true;
landlock: Set up the security framework and manage credentials Process's credentials point to a Landlock domain, which is underneath implemented with a ruleset. In the following commits, this domain is used to check and enforce the ptrace and filesystem security policies. A domain is inherited from a parent to its child the same way a thread inherits a seccomp policy. Cc: James Morris <jmorris@namei.org> Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com> Reviewed-by: Jann Horn <jannh@google.com> Acked-by: Serge Hallyn <serge@hallyn.com> Reviewed-by: Kees Cook <keescook@chromium.org> Link: https://lore.kernel.org/r/20210422154123.13086-4-mic@digikod.net Signed-off-by: James Morris <jamorris@linux.microsoft.com>
2021-04-22 15:41:13 +00:00
pr_info("Up and running.\n");
return 0;
}
DEFINE_LSM(LANDLOCK_NAME) = {
.name = LANDLOCK_NAME,
.init = landlock_init,
.blobs = &landlock_blob_sizes,
};
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