[PATCH] landlock: Use bit-fields for storing handled layer access masks
Günther Noack
gnoack at google.com
Mon Jun 10 08:21:15 UTC 2024
When defined using bit-fields, the compiler takes care of packing the
bits in a memory-efficient way and frees us from defining
LANDLOCK_SHIFT_ACCESS_* by hand. The exact memory layout does not
matter in our use case.
The manual definition of LANDLOCK_SHIFT_ACCESS_* has resulted in bugs
in at least two recent patch sets where new kinds of handled access
rights were introduced.
Cc: Mikhail Ivanov <ivanov.mikhail1 at huawei-partners.com>
Cc: Tahera Fahimi <fahimitahera at gmail.com>
Link: https://lore.kernel.org/all/ebd680cc-25d6-ee14-4856-310f5e5e28e4@huawei-partners.com/
Link: https://lore.kernel.org/all/ZmLEoBfHyUR3nKAV@google.com/
Signed-off-by: Günther Noack <gnoack at google.com>
---
security/landlock/limits.h | 2 --
security/landlock/ruleset.c | 4 ----
security/landlock/ruleset.h | 24 +++++++++---------------
3 files changed, 9 insertions(+), 21 deletions(-)
diff --git a/security/landlock/limits.h b/security/landlock/limits.h
index 20fdb5ff3514..4eb643077a2a 100644
--- a/security/landlock/limits.h
+++ b/security/landlock/limits.h
@@ -21,12 +21,10 @@
#define LANDLOCK_LAST_ACCESS_FS LANDLOCK_ACCESS_FS_IOCTL_DEV
#define LANDLOCK_MASK_ACCESS_FS ((LANDLOCK_LAST_ACCESS_FS << 1) - 1)
#define LANDLOCK_NUM_ACCESS_FS __const_hweight64(LANDLOCK_MASK_ACCESS_FS)
-#define LANDLOCK_SHIFT_ACCESS_FS 0
#define LANDLOCK_LAST_ACCESS_NET LANDLOCK_ACCESS_NET_CONNECT_TCP
#define LANDLOCK_MASK_ACCESS_NET ((LANDLOCK_LAST_ACCESS_NET << 1) - 1)
#define LANDLOCK_NUM_ACCESS_NET __const_hweight64(LANDLOCK_MASK_ACCESS_NET)
-#define LANDLOCK_SHIFT_ACCESS_NET LANDLOCK_NUM_ACCESS_FS
/* clang-format on */
diff --git a/security/landlock/ruleset.c b/security/landlock/ruleset.c
index e0a5fbf9201a..6ff232f58618 100644
--- a/security/landlock/ruleset.c
+++ b/security/landlock/ruleset.c
@@ -169,13 +169,9 @@ static void build_check_ruleset(void)
.num_rules = ~0,
.num_layers = ~0,
};
- typeof(ruleset.access_masks[0]) access_masks = ~0;
BUILD_BUG_ON(ruleset.num_rules < LANDLOCK_MAX_NUM_RULES);
BUILD_BUG_ON(ruleset.num_layers < LANDLOCK_MAX_NUM_LAYERS);
- BUILD_BUG_ON(access_masks <
- ((LANDLOCK_MASK_ACCESS_FS << LANDLOCK_SHIFT_ACCESS_FS) |
- (LANDLOCK_MASK_ACCESS_NET << LANDLOCK_SHIFT_ACCESS_NET)));
}
/**
diff --git a/security/landlock/ruleset.h b/security/landlock/ruleset.h
index c7f1526784fd..0f1b5b4c8f6b 100644
--- a/security/landlock/ruleset.h
+++ b/security/landlock/ruleset.h
@@ -39,10 +39,10 @@ static_assert(BITS_PER_TYPE(access_mask_t) >= LANDLOCK_NUM_ACCESS_NET);
static_assert(sizeof(unsigned long) >= sizeof(access_mask_t));
/* Ruleset access masks. */
-typedef u32 access_masks_t;
-/* Makes sure all ruleset access rights can be stored. */
-static_assert(BITS_PER_TYPE(access_masks_t) >=
- LANDLOCK_NUM_ACCESS_FS + LANDLOCK_NUM_ACCESS_NET);
+struct access_masks {
+ access_mask_t fs : LANDLOCK_NUM_ACCESS_FS;
+ access_mask_t net : LANDLOCK_NUM_ACCESS_NET;
+};
typedef u16 layer_mask_t;
/* Makes sure all layers can be checked. */
@@ -226,7 +226,7 @@ struct landlock_ruleset {
* layers are set once and never changed for the
* lifetime of the ruleset.
*/
- access_masks_t access_masks[];
+ struct access_masks access_masks[];
};
};
};
@@ -265,8 +265,7 @@ landlock_add_fs_access_mask(struct landlock_ruleset *const ruleset,
/* Should already be checked in sys_landlock_create_ruleset(). */
WARN_ON_ONCE(fs_access_mask != fs_mask);
- ruleset->access_masks[layer_level] |=
- (fs_mask << LANDLOCK_SHIFT_ACCESS_FS);
+ ruleset->access_masks[layer_level].fs |= fs_mask;
}
static inline void
@@ -278,17 +277,14 @@ landlock_add_net_access_mask(struct landlock_ruleset *const ruleset,
/* Should already be checked in sys_landlock_create_ruleset(). */
WARN_ON_ONCE(net_access_mask != net_mask);
- ruleset->access_masks[layer_level] |=
- (net_mask << LANDLOCK_SHIFT_ACCESS_NET);
+ ruleset->access_masks[layer_level].net |= net_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] >>
- LANDLOCK_SHIFT_ACCESS_FS) &
- LANDLOCK_MASK_ACCESS_FS;
+ return ruleset->access_masks[layer_level].fs;
}
static inline access_mask_t
@@ -304,9 +300,7 @@ static inline access_mask_t
landlock_get_net_access_mask(const struct landlock_ruleset *const ruleset,
const u16 layer_level)
{
- return (ruleset->access_masks[layer_level] >>
- LANDLOCK_SHIFT_ACCESS_NET) &
- LANDLOCK_MASK_ACCESS_NET;
+ return ruleset->access_masks[layer_level].net;
}
bool landlock_unmask_layers(const struct landlock_rule *const rule,
--
2.45.2.505.gda0bf45e8d-goog
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