On 19/03/2021 19:13, Kees Cook wrote: > On Tue, Mar 16, 2021 at 09:42:41PM +0100, Mickaël Salaün wrote: >> From: Mickaël Salaün <mic@xxxxxxxxxxxxxxxxxxx> >> >> A Landlock object enables to identify a kernel object (e.g. an inode). >> A Landlock rule is a set of access rights allowed on an object. Rules >> are grouped in rulesets that may be tied to a set of processes (i.e. >> subjects) to enforce a scoped access-control (i.e. a domain). >> >> Because Landlock's goal is to empower any process (especially >> unprivileged ones) to sandbox themselves, we cannot rely on a >> system-wide object identification such as file extended attributes. >> Indeed, we need innocuous, composable and modular access-controls. >> >> The main challenge with these constraints is to identify kernel objects >> while this identification is useful (i.e. when a security policy makes >> use of this object). But this identification data should be freed once >> no policy is using it. This ephemeral tagging should not and may not be >> written in the filesystem. We then need to manage the lifetime of a >> rule according to the lifetime of its objects. To avoid a global lock, >> this implementation make use of RCU and counters to safely reference >> objects. >> >> A following commit uses this generic object management for inodes. >> >> Cc: James Morris <jmorris@xxxxxxxxx> >> Cc: Kees Cook <keescook@xxxxxxxxxxxx> >> Signed-off-by: Mickaël Salaün <mic@xxxxxxxxxxxxxxxxxxx> >> Reviewed-by: Jann Horn <jannh@xxxxxxxxxx> >> Acked-by: Serge Hallyn <serge@xxxxxxxxxx> >> Link: https://lore.kernel.org/r/20210316204252.427806-2-mic@xxxxxxxxxxx >> --- >> >> Changes since v28: >> * Improve Kconfig description (suggested by Serge Hallyn). >> * Add Acked-by Serge Hallyn. >> * Clean up comment. >> >> Changes since v27: >> * Update Kconfig for landlock_restrict_self(2). >> * Cosmetic fixes: use 80 columns in Kconfig and align Makefile >> declarations. >> >> Changes since v26: >> * Update Kconfig for landlock_enforce_ruleset_self(2). >> * Fix spelling. >> >> Changes since v24: >> * Fix typo in comment (spotted by Jann Horn). >> * Add Reviewed-by: Jann Horn <jannh@xxxxxxxxxx> >> >> Changes since v23: >> * Update landlock_create_object() to return error codes instead of NULL. >> This help error handling in callers. >> * When using make oldconfig with a previous configuration already >> including the CONFIG_LSM variable, no question is asked to update its >> content. Update the Kconfig help to warn about LSM stacking >> configuration. >> * Constify variable (spotted by Vincent Dagonneau). >> >> Changes since v22: >> * Fix spelling (spotted by Jann Horn). >> >> Changes since v21: >> * Update Kconfig help. >> * Clean up comments. >> >> Changes since v18: >> * Account objects to kmemcg. >> >> Changes since v14: >> * Simplify the object, rule and ruleset management at the expense of a >> less aggressive memory freeing (contributed by Jann Horn, with >> additional modifications): >> - Remove object->list aggregating the rules tied to an object. >> - Remove landlock_get_object(), landlock_drop_object(), >> {get,put}_object_cleaner() and landlock_rule_is_disabled(). >> - Rewrite landlock_put_object() to use a more simple mechanism >> (no tricky RCU). >> - Replace enum landlock_object_type and landlock_release_object() with >> landlock_object_underops->release() >> - Adjust unions and Sparse annotations. >> Cf. https://lore.kernel.org/lkml/CAG48ez21bEn0wL1bbmTiiu8j9jP5iEWtHOwz4tURUJ+ki0ydYw@xxxxxxxxxxxxxx/ >> * Merge struct landlock_rule into landlock_ruleset_elem to simplify the >> rule management. >> * Constify variables. >> * Improve kernel documentation. >> * Cosmetic variable renames. >> * Remove the "default" in the Kconfig (suggested by Jann Horn). >> * Only use refcount_inc() through getter helpers. >> * Update Kconfig description. >> >> Changes since v13: >> * New dedicated implementation, removing the need for eBPF. >> >> Previous changes: >> https://lore.kernel.org/lkml/20190721213116.23476-6-mic@xxxxxxxxxxx/ >> --- >> MAINTAINERS | 10 +++++ >> security/Kconfig | 1 + >> security/Makefile | 2 + >> security/landlock/Kconfig | 21 +++++++++ >> security/landlock/Makefile | 3 ++ >> security/landlock/object.c | 67 ++++++++++++++++++++++++++++ >> security/landlock/object.h | 91 ++++++++++++++++++++++++++++++++++++++ >> 7 files changed, 195 insertions(+) >> create mode 100644 security/landlock/Kconfig >> create mode 100644 security/landlock/Makefile >> create mode 100644 security/landlock/object.c >> create mode 100644 security/landlock/object.h >> >> diff --git a/MAINTAINERS b/MAINTAINERS >> index aa84121c5611..87a2738dfdec 100644 >> --- a/MAINTAINERS >> +++ b/MAINTAINERS >> @@ -9997,6 +9997,16 @@ F: net/core/sock_map.c >> F: net/ipv4/tcp_bpf.c >> F: net/ipv4/udp_bpf.c >> >> +LANDLOCK SECURITY MODULE >> +M: Mickaël Salaün <mic@xxxxxxxxxxx> >> +L: linux-security-module@xxxxxxxxxxxxxxx >> +S: Supported >> +W: https://landlock.io >> +T: git https://github.com/landlock-lsm/linux.git >> +F: security/landlock/ >> +K: landlock >> +K: LANDLOCK >> + >> LANTIQ / INTEL Ethernet drivers >> M: Hauke Mehrtens <hauke@xxxxxxxxxx> >> L: netdev@xxxxxxxxxxxxxxx >> diff --git a/security/Kconfig b/security/Kconfig >> index 7561f6f99f1d..15a4342b5d01 100644 >> --- a/security/Kconfig >> +++ b/security/Kconfig >> @@ -238,6 +238,7 @@ source "security/loadpin/Kconfig" >> source "security/yama/Kconfig" >> source "security/safesetid/Kconfig" >> source "security/lockdown/Kconfig" >> +source "security/landlock/Kconfig" >> >> source "security/integrity/Kconfig" >> >> diff --git a/security/Makefile b/security/Makefile >> index 3baf435de541..47e432900e24 100644 >> --- a/security/Makefile >> +++ b/security/Makefile >> @@ -13,6 +13,7 @@ subdir-$(CONFIG_SECURITY_LOADPIN) += loadpin >> subdir-$(CONFIG_SECURITY_SAFESETID) += safesetid >> subdir-$(CONFIG_SECURITY_LOCKDOWN_LSM) += lockdown >> subdir-$(CONFIG_BPF_LSM) += bpf >> +subdir-$(CONFIG_SECURITY_LANDLOCK) += landlock >> >> # always enable default capabilities >> obj-y += commoncap.o >> @@ -32,6 +33,7 @@ obj-$(CONFIG_SECURITY_SAFESETID) += safesetid/ >> obj-$(CONFIG_SECURITY_LOCKDOWN_LSM) += lockdown/ >> obj-$(CONFIG_CGROUPS) += device_cgroup.o >> obj-$(CONFIG_BPF_LSM) += bpf/ >> +obj-$(CONFIG_SECURITY_LANDLOCK) += landlock/ >> >> # Object integrity file lists >> subdir-$(CONFIG_INTEGRITY) += integrity >> diff --git a/security/landlock/Kconfig b/security/landlock/Kconfig >> new file mode 100644 >> index 000000000000..c1e862a38410 >> --- /dev/null >> +++ b/security/landlock/Kconfig >> @@ -0,0 +1,21 @@ >> +# SPDX-License-Identifier: GPL-2.0-only >> + >> +config SECURITY_LANDLOCK >> + bool "Landlock support" >> + depends on SECURITY >> + select SECURITY_PATH >> + help >> + Landlock is a sandboxing mechanism that enables processes to restrict >> + themselves (and their future children) by gradually enforcing >> + tailored access control policies. A Landlock security policy is a >> + set of access rights (e.g. open a file in read-only, make a >> + directory, etc.) tied to a file hierarchy. Such policy can be >> + configured and enforced by any processes for themselves using the >> + dedicated system calls: landlock_create_ruleset(), >> + landlock_add_rule(), and landlock_restrict_self(). >> + >> + See Documentation/userspace-api/landlock.rst for further information. >> + >> + If you are unsure how to answer this question, answer N. Otherwise, >> + you should also prepend "landlock," to the content of CONFIG_LSM to >> + enable Landlock at boot time. >> diff --git a/security/landlock/Makefile b/security/landlock/Makefile >> new file mode 100644 >> index 000000000000..cb6deefbf4c0 >> --- /dev/null >> +++ b/security/landlock/Makefile >> @@ -0,0 +1,3 @@ >> +obj-$(CONFIG_SECURITY_LANDLOCK) := landlock.o >> + >> +landlock-y := object.o >> diff --git a/security/landlock/object.c b/security/landlock/object.c >> new file mode 100644 >> index 000000000000..d674fdf9ff04 >> --- /dev/null >> +++ b/security/landlock/object.c >> @@ -0,0 +1,67 @@ >> +// SPDX-License-Identifier: GPL-2.0-only >> +/* >> + * Landlock LSM - Object management >> + * >> + * Copyright © 2016-2020 Mickaël Salaün <mic@xxxxxxxxxxx> >> + * Copyright © 2018-2020 ANSSI >> + */ >> + >> +#include <linux/bug.h> >> +#include <linux/compiler_types.h> >> +#include <linux/err.h> >> +#include <linux/kernel.h> >> +#include <linux/rcupdate.h> >> +#include <linux/refcount.h> >> +#include <linux/slab.h> >> +#include <linux/spinlock.h> >> + >> +#include "object.h" >> + >> +struct landlock_object *landlock_create_object( >> + const struct landlock_object_underops *const underops, >> + void *const underobj) >> +{ >> + struct landlock_object *new_object; >> + >> + if (WARN_ON_ONCE(!underops || !underobj)) >> + return ERR_PTR(-ENOENT); >> + new_object = kzalloc(sizeof(*new_object), GFP_KERNEL_ACCOUNT); > > Is there any benefit to using a dedicated kmem_cache instead of kmalloc? > I see later that you end up with variable-sized allocations, so this > might be fine as-is. I though about that, but for the sake of simplicity I choose to not use that in this series. It may comes with a future update if there is a visible performance improvement though. > >> + if (!new_object) >> + return ERR_PTR(-ENOMEM); >> + refcount_set(&new_object->usage, 1); >> + spin_lock_init(&new_object->lock); >> + new_object->underops = underops; >> + new_object->underobj = underobj; >> + return new_object; >> +} >> + >> +/* >> + * The caller must own the object (i.e. thanks to object->usage) to safely put >> + * it. >> + */ >> +void landlock_put_object(struct landlock_object *const object) >> +{ >> + /* >> + * The call to @object->underops->release(object) might sleep, e.g. >> + * because of iput(). >> + */ >> + might_sleep(); >> + if (!object) >> + return; >> + >> + /* >> + * If the @object's refcount cannot drop to zero, we can just decrement >> + * the refcount without holding a lock. Otherwise, the decrement must >> + * happen under @object->lock for synchronization with things like >> + * get_inode_object(). >> + */ >> + if (refcount_dec_and_lock(&object->usage, &object->lock)) { >> + __acquire(&object->lock); >> + /* >> + * With @object->lock initially held, remove the reference from >> + * @object->underobj to @object (if it still exists). >> + */ >> + object->underops->release(object); >> + kfree_rcu(object, rcu_free); >> + } >> +} >> diff --git a/security/landlock/object.h b/security/landlock/object.h >> new file mode 100644 >> index 000000000000..3e5d5b6941c3 >> --- /dev/null >> +++ b/security/landlock/object.h >> @@ -0,0 +1,91 @@ >> +/* SPDX-License-Identifier: GPL-2.0-only */ >> +/* >> + * Landlock LSM - Object management >> + * >> + * Copyright © 2016-2020 Mickaël Salaün <mic@xxxxxxxxxxx> >> + * Copyright © 2018-2020 ANSSI >> + */ >> + >> +#ifndef _SECURITY_LANDLOCK_OBJECT_H >> +#define _SECURITY_LANDLOCK_OBJECT_H >> + >> +#include <linux/compiler_types.h> >> +#include <linux/refcount.h> >> +#include <linux/spinlock.h> >> + >> +struct landlock_object; >> + >> +/** >> + * struct landlock_object_underops - Operations on an underlying object >> + */ >> +struct landlock_object_underops { >> + /** >> + * @release: Releases the underlying object (e.g. iput() for an inode). >> + */ >> + void (*release)(struct landlock_object *const object) >> + __releases(object->lock); >> +}; >> + >> +/** >> + * struct landlock_object - Security blob tied to a kernel object >> + * >> + * The goal of this structure is to enable to tie a set of ephemeral access >> + * rights (pertaining to different domains) to a kernel object (e.g an inode) >> + * in a safe way. This implies to handle concurrent use and modification. >> + * >> + * The lifetime of a &struct landlock_object depends of the rules referring to >> + * it. >> + */ >> +struct landlock_object { >> + /** >> + * @usage: This counter is used to tie an object to the rules matching >> + * it or to keep it alive while adding a new rule. If this counter >> + * reaches zero, this struct must not be modified, but this counter can >> + * still be read from within an RCU read-side critical section. When >> + * adding a new rule to an object with a usage counter of zero, we must >> + * wait until the pointer to this object is set to NULL (or recycled). >> + */ >> + refcount_t usage; >> + /** >> + * @lock: Protects against concurrent modifications. This lock must be >> + * held from the time @usage drops to zero until any weak references >> + * from @underobj to this object have been cleaned up. >> + * >> + * Lock ordering: inode->i_lock nests inside this. >> + */ >> + spinlock_t lock; >> + /** >> + * @underobj: Used when cleaning up an object and to mark an object as >> + * tied to its underlying kernel structure. This pointer is protected >> + * by @lock. Cf. landlock_release_inodes() and release_inode(). >> + */ >> + void *underobj; >> + union { >> + /** >> + * @rcu_free: Enables lockless use of @usage, @lock and >> + * @underobj from within an RCU read-side critical section. >> + * @rcu_free and @underops are only used by >> + * landlock_put_object(). >> + */ >> + struct rcu_head rcu_free; >> + /** >> + * @underops: Enables landlock_put_object() to release the >> + * underlying object (e.g. inode). >> + */ >> + const struct landlock_object_underops *underops; >> + }; >> +}; >> + >> +struct landlock_object *landlock_create_object( >> + const struct landlock_object_underops *const underops, >> + void *const underobj); >> + >> +void landlock_put_object(struct landlock_object *const object); >> + >> +static inline void landlock_get_object(struct landlock_object *const object) >> +{ >> + if (object) >> + refcount_inc(&object->usage); >> +} >> + >> +#endif /* _SECURITY_LANDLOCK_OBJECT_H */ >> -- >> 2.30.2 >> > > Either way, this object lifetime management looks okay to me: > > Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> >
