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Message-ID: <20241022151144.872797-2-mic@digikod.net>
Date: Tue, 22 Oct 2024 17:11:42 +0200
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 v3 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/20241022151144.872797-2-mic@digikod.net
---
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 | 70 +++++++++++++++++++++++++++++++-----
security/landlock/syscalls.c | 2 +-
3 files changed, 70 insertions(+), 33 deletions(-)
diff --git a/security/landlock/fs.c b/security/landlock/fs.c
index 7d79fc8abe21..dd9a7297ea4e 100644
--- a/security/landlock/fs.c
+++ b/security/landlock/fs.c
@@ -388,38 +388,21 @@ 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_merge_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_match_ruleset(landlock_get_current_domain(), any_fs);
}
/*
@@ -1516,8 +1499,8 @@ static int hook_file_open(struct file *const file)
layer_mask_t layer_masks[LANDLOCK_NUM_ACCESS_FS] = {};
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);
+ const struct landlock_ruleset *const dom = landlock_match_ruleset(
+ 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..e00edcb38c5b 100644
--- a/security/landlock/ruleset.h
+++ b/security/landlock/ruleset.h
@@ -47,6 +47,15 @@ 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(((union access_masks_all *)NULL)->masks) ==
+ sizeof(((union access_masks_all *)NULL)->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 +269,58 @@ static inline void landlock_get_ruleset(struct landlock_ruleset *const ruleset)
refcount_inc(&ruleset->usage);
}
+/**
+ * landlock_merge_access_masks - Return the merge of a ruleset's access_masks
+ *
+ * @ruleset: Landlock ruleset (used as a domain)
+ *
+ * Returns: an access_masks result of the OR of all the ruleset's access masks.
+ */
+static inline struct access_masks
+landlock_merge_access_masks(const struct landlock_ruleset *const ruleset)
+{
+ union access_masks_all matches = {};
+ size_t layer_level;
+
+ for (layer_level = 0; layer_level < ruleset->num_layers;
+ layer_level++) {
+ union access_masks_all layer = {
+ .masks = ruleset->access_masks[layer_level],
+ };
+
+ matches.all |= layer.all;
+ }
+
+ return matches.masks;
+}
+
+/**
+ * landlock_match_ruleset - Return @ruleset if any @masks right matches
+ *
+ * @ruleset: Landlock ruleset (used as a domain)
+ * @masks: access masks
+ *
+ * Returns: @ruleset if @masks matches, or NULL otherwise.
+ */
+static inline const struct landlock_ruleset *
+landlock_match_ruleset(const struct landlock_ruleset *const ruleset,
+ const struct access_masks masks)
+{
+ const union access_masks_all masks_all = {
+ .masks = masks,
+ };
+ union access_masks_all merge = {};
+
+ if (!ruleset)
+ return NULL;
+
+ merge.masks = landlock_merge_access_masks(ruleset);
+ if (merge.all & masks_all.all)
+ return ruleset;
+
+ return NULL;
+}
+
static inline void
landlock_add_fs_access_mask(struct landlock_ruleset *const ruleset,
const access_mask_t fs_access_mask,
@@ -295,19 +356,12 @@ 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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