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Message-ID: <20241109110856.222842-2-mic@digikod.net>
Date: Sat, 9 Nov 2024 12:08:54 +0100
From: Mickaël Salaün <mic@...ikod.net>
To: Günther Noack <gnoack@...gle.com>,
Mikhail Ivanov <ivanov.mikhail1@...wei-partners.com>
Cc: Mickaël Salaün <mic@...ikod.net>,
Konstantin Meskhidze <konstantin.meskhidze@...wei.com>,
Paul Moore <paul@...l-moore.com>,
Tahera Fahimi <fahimitahera@...il.com>,
linux-kernel@...r.kernel.org,
linux-security-module@...r.kernel.org
Subject: [PATCH v4 1/3] landlock: Refactor filesystem access mask management
Replace get_raw_handled_fs_accesses() with a generic
landlock_merge_access_masks(), and replace get_fs_domain() with a
generic landlock_match_ruleset(). These helpers will also be useful for
other types of access.
Cc: Günther Noack <gnoack@...gle.com>
Cc: Mikhail Ivanov <ivanov.mikhail1@...wei-partners.com>
Signed-off-by: Mickaël Salaün <mic@...ikod.net>
Link: https://lore.kernel.org/r/20241109110856.222842-2-mic@digikod.net
---
Changes since v3:
* Rename landlock_merge_access_masks() to landlock_union_access_masks(),
suggested by Günther.
* Rename landlock_match_ruleset() to landlock_get_applicable_domain(),
suggested by Günther.
* Rename the "ruleset" arguments to "domain" for consistency with these
new helpers.
* Use typeof_member(), suggested by Günther. Also include kernel.h
(instead of the new container_of.h to ease backports).
Changes since v2:
* Create a new type union access_masks_all instead of changing struct
acces_masks.
* Replace get_fs_domain() with an explicit call to
landlock_match_ruleset().
Changes since v1:
* Rename landlock_filter_access_masks() to landlock_match_ruleset().
* Rename local variables from domain to ruleset to mach helpers'
semantic. We'll rename and move these helpers when we'll have a
dedicated domain struct type.
* Rename the all_fs mask to any_fs.
* Add documentation, as suggested by Günther.
---
security/landlock/fs.c | 31 ++++-----------
security/landlock/ruleset.h | 73 ++++++++++++++++++++++++++++++++----
security/landlock/syscalls.c | 2 +-
3 files changed, 74 insertions(+), 32 deletions(-)
diff --git a/security/landlock/fs.c b/security/landlock/fs.c
index 7d79fc8abe21..e31b97a9f175 100644
--- a/security/landlock/fs.c
+++ b/security/landlock/fs.c
@@ -388,38 +388,22 @@ static bool is_nouser_or_private(const struct dentry *dentry)
unlikely(IS_PRIVATE(d_backing_inode(dentry))));
}
-static access_mask_t
-get_raw_handled_fs_accesses(const struct landlock_ruleset *const domain)
-{
- access_mask_t access_dom = 0;
- size_t layer_level;
-
- for (layer_level = 0; layer_level < domain->num_layers; layer_level++)
- access_dom |=
- landlock_get_raw_fs_access_mask(domain, layer_level);
- return access_dom;
-}
-
static access_mask_t
get_handled_fs_accesses(const struct landlock_ruleset *const domain)
{
/* Handles all initially denied by default access rights. */
- return get_raw_handled_fs_accesses(domain) |
+ return landlock_union_access_masks(domain).fs |
LANDLOCK_ACCESS_FS_INITIALLY_DENIED;
}
-static const struct landlock_ruleset *
-get_fs_domain(const struct landlock_ruleset *const domain)
-{
- if (!domain || !get_raw_handled_fs_accesses(domain))
- return NULL;
-
- return domain;
-}
+static const struct access_masks any_fs = {
+ .fs = ~0,
+};
static const struct landlock_ruleset *get_current_fs_domain(void)
{
- return get_fs_domain(landlock_get_current_domain());
+ return landlock_get_applicable_domain(landlock_get_current_domain(),
+ any_fs);
}
/*
@@ -1517,7 +1501,8 @@ static int hook_file_open(struct file *const file)
access_mask_t open_access_request, full_access_request, allowed_access,
optional_access;
const struct landlock_ruleset *const dom =
- get_fs_domain(landlock_cred(file->f_cred)->domain);
+ landlock_get_applicable_domain(
+ landlock_cred(file->f_cred)->domain, any_fs);
if (!dom)
return 0;
diff --git a/security/landlock/ruleset.h b/security/landlock/ruleset.h
index 61bdbc550172..698fa3114cf4 100644
--- a/security/landlock/ruleset.h
+++ b/security/landlock/ruleset.h
@@ -11,6 +11,7 @@
#include <linux/bitops.h>
#include <linux/build_bug.h>
+#include <linux/kernel.h>
#include <linux/mutex.h>
#include <linux/rbtree.h>
#include <linux/refcount.h>
@@ -47,6 +48,15 @@ struct access_masks {
access_mask_t scope : LANDLOCK_NUM_SCOPE;
};
+union access_masks_all {
+ struct access_masks masks;
+ u32 all;
+};
+
+/* Makes sure all fields are covered. */
+static_assert(sizeof(typeof_member(union access_masks_all, masks)) ==
+ sizeof(typeof_member(union access_masks_all, all)));
+
typedef u16 layer_mask_t;
/* Makes sure all layers can be checked. */
static_assert(BITS_PER_TYPE(layer_mask_t) >= LANDLOCK_MAX_NUM_LAYERS);
@@ -260,6 +270,60 @@ static inline void landlock_get_ruleset(struct landlock_ruleset *const ruleset)
refcount_inc(&ruleset->usage);
}
+/**
+ * landlock_union_access_masks - Return all access rights handled in the
+ * domain
+ *
+ * @domain: Landlock ruleset (used as a domain)
+ *
+ * Returns: an access_masks result of the OR of all the domain's access masks.
+ */
+static inline struct access_masks
+landlock_union_access_masks(const struct landlock_ruleset *const domain)
+{
+ union access_masks_all matches = {};
+ size_t layer_level;
+
+ for (layer_level = 0; layer_level < domain->num_layers; layer_level++) {
+ union access_masks_all layer = {
+ .masks = domain->access_masks[layer_level],
+ };
+
+ matches.all |= layer.all;
+ }
+
+ return matches.masks;
+}
+
+/**
+ * landlock_get_applicable_domain - Return @domain if it applies to (handles)
+ * the access rights specified in @masks
+ *
+ * @domain: Landlock ruleset (used as a domain)
+ * @masks: access masks
+ *
+ * Returns: @domain if any access rights specified in @masks is handled, or
+ * NULL otherwise.
+ */
+static inline const struct landlock_ruleset *
+landlock_get_applicable_domain(const struct landlock_ruleset *const domain,
+ const struct access_masks masks)
+{
+ const union access_masks_all masks_all = {
+ .masks = masks,
+ };
+ union access_masks_all merge = {};
+
+ if (!domain)
+ return NULL;
+
+ merge.masks = landlock_union_access_masks(domain);
+ if (merge.all & masks_all.all)
+ return domain;
+
+ return NULL;
+}
+
static inline void
landlock_add_fs_access_mask(struct landlock_ruleset *const ruleset,
const access_mask_t fs_access_mask,
@@ -295,19 +359,12 @@ landlock_add_scope_mask(struct landlock_ruleset *const ruleset,
ruleset->access_masks[layer_level].scope |= mask;
}
-static inline access_mask_t
-landlock_get_raw_fs_access_mask(const struct landlock_ruleset *const ruleset,
- const u16 layer_level)
-{
- return ruleset->access_masks[layer_level].fs;
-}
-
static inline access_mask_t
landlock_get_fs_access_mask(const struct landlock_ruleset *const ruleset,
const u16 layer_level)
{
/* Handles all initially denied by default access rights. */
- return landlock_get_raw_fs_access_mask(ruleset, layer_level) |
+ return ruleset->access_masks[layer_level].fs |
LANDLOCK_ACCESS_FS_INITIALLY_DENIED;
}
diff --git a/security/landlock/syscalls.c b/security/landlock/syscalls.c
index f5a0e7182ec0..c097d356fa45 100644
--- a/security/landlock/syscalls.c
+++ b/security/landlock/syscalls.c
@@ -329,7 +329,7 @@ static int add_rule_path_beneath(struct landlock_ruleset *const ruleset,
return -ENOMSG;
/* Checks that allowed_access matches the @ruleset constraints. */
- mask = landlock_get_raw_fs_access_mask(ruleset, 0);
+ mask = ruleset->access_masks[0].fs;
if ((path_beneath_attr.allowed_access | mask) != mask)
return -EINVAL;
--
2.47.0
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