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. > + 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> -- Kees Cook
