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Message-ID: <94ed4212-c093-9c5c-089f-e9e4097e5bd6@digikod.net>
Date: Thu, 17 Nov 2022 19:41:00 +0100
From: Mickaël Salaün <mic@...ikod.net>
To: Konstantin Meskhidze <konstantin.meskhidze@...wei.com>
Cc: willemdebruijn.kernel@...il.com, gnoack3000@...il.com,
linux-security-module@...r.kernel.org, netdev@...r.kernel.org,
netfilter-devel@...r.kernel.org, artem.kuzin@...wei.com
Subject: Re: [PATCH v8 01/12] landlock: Make ruleset's access masks more
generic
On 21/10/2022 17:26, Konstantin Meskhidze wrote:
> To support network type rules, this modification renames ruleset's
> access masks and modifies it's type to access_masks_t. This patch
> adds filesystem helper functions to add and get filesystem mask.
>
> Signed-off-by: Konstantin Meskhidze <konstantin.meskhidze@...wei.com>
> ---
>
> Changes since v7:
> * Refactors commit message.
>
> Changes since v6:
> * Adds a new access_masks_t for struct ruleset.
> * Renames landlock_set_fs_access_mask() to landlock_add_fs_access_mask()
> because it OR values.
> * Makes landlock_add_fs_access_mask() more resilient incorrect values.
> * Refactors landlock_get_fs_access_mask().
>
> Changes since v6:
> * Adds a new access_masks_t for struct ruleset.
> * Renames landlock_set_fs_access_mask() to landlock_add_fs_access_mask()
> because it OR values.
> * Makes landlock_add_fs_access_mask() more resilient incorrect values.
> * Refactors landlock_get_fs_access_mask().
>
> Changes since v5:
> * Changes access_mask_t to u32.
> * Formats code with clang-format-14.
>
> Changes since v4:
> * Deletes struct landlock_access_mask.
>
> Changes since v3:
> * Splits commit.
> * Adds get_mask, set_mask helpers for filesystem.
> * Adds new struct landlock_access_mask.
>
> ---
> security/landlock/fs.c | 10 +++++-----
> security/landlock/limits.h | 1 +
> security/landlock/ruleset.c | 17 +++++++++--------
> security/landlock/ruleset.h | 35 +++++++++++++++++++++++++++++++----
> security/landlock/syscalls.c | 7 ++++---
> 5 files changed, 50 insertions(+), 20 deletions(-)
>
> diff --git a/security/landlock/fs.c b/security/landlock/fs.c
> index adcea0fe7e68..0d57c6479d29 100644
> --- a/security/landlock/fs.c
> +++ b/security/landlock/fs.c
> @@ -178,9 +178,9 @@ int landlock_append_fs_rule(struct landlock_ruleset *const ruleset,
> return -EINVAL;
>
> /* Transforms relative access rights to absolute ones. */
> - access_rights |=
> - LANDLOCK_MASK_ACCESS_FS &
> - ~(ruleset->fs_access_masks[0] | ACCESS_INITIALLY_DENIED);
> + access_rights |= LANDLOCK_MASK_ACCESS_FS &
> + ~(landlock_get_fs_access_mask(ruleset, 0) |
> + ACCESS_INITIALLY_DENIED);
> object = get_inode_object(d_backing_inode(path->dentry));
> if (IS_ERR(object))
> return PTR_ERR(object);
> @@ -294,7 +294,7 @@ get_handled_accesses(const struct landlock_ruleset *const domain)
> size_t layer_level;
>
> for (layer_level = 0; layer_level < domain->num_layers; layer_level++)
> - access_dom |= domain->fs_access_masks[layer_level];
> + access_dom |= landlock_get_fs_access_mask(domain, layer_level);
> return access_dom & LANDLOCK_MASK_ACCESS_FS;
You can remove `& LANDLOCK_MASK_ACCESS_FS` here because it is now part
of landlock_get_fs_access_mask().
> }
>
> @@ -336,7 +336,7 @@ init_layer_masks(const struct landlock_ruleset *const domain,
> * access rights.
> */
> if (BIT_ULL(access_bit) &
> - (domain->fs_access_masks[layer_level] |
> + (landlock_get_fs_access_mask(domain, layer_level) |
> ACCESS_INITIALLY_DENIED)) {
> (*layer_masks)[access_bit] |=
> BIT_ULL(layer_level);
> diff --git a/security/landlock/limits.h b/security/landlock/limits.h
> index 82288f0e9e5e..bafb3b8dc677 100644
> --- a/security/landlock/limits.h
> +++ b/security/landlock/limits.h
> @@ -21,6 +21,7 @@
> #define LANDLOCK_LAST_ACCESS_FS LANDLOCK_ACCESS_FS_TRUNCATE
> #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
>
> /* clang-format on */
>
> diff --git a/security/landlock/ruleset.c b/security/landlock/ruleset.c
> index 996484f98bfd..1f3188b4e313 100644
> --- a/security/landlock/ruleset.c
> +++ b/security/landlock/ruleset.c
> @@ -29,7 +29,7 @@ static struct landlock_ruleset *create_ruleset(const u32 num_layers)
> struct landlock_ruleset *new_ruleset;
>
> new_ruleset =
> - kzalloc(struct_size(new_ruleset, fs_access_masks, num_layers),
> + kzalloc(struct_size(new_ruleset, access_masks, num_layers),
> GFP_KERNEL_ACCOUNT);
> if (!new_ruleset)
> return ERR_PTR(-ENOMEM);
> @@ -40,7 +40,7 @@ static struct landlock_ruleset *create_ruleset(const u32 num_layers)
> /*
> * hierarchy = NULL
> * num_rules = 0
> - * fs_access_masks[] = 0
> + * access_masks[] = 0
> */
> return new_ruleset;
> }
> @@ -55,7 +55,7 @@ landlock_create_ruleset(const access_mask_t fs_access_mask)
> return ERR_PTR(-ENOMSG);
> new_ruleset = create_ruleset(1);
> if (!IS_ERR(new_ruleset))
> - new_ruleset->fs_access_masks[0] = fs_access_mask;
> + landlock_add_fs_access_mask(new_ruleset, fs_access_mask, 0);
> return new_ruleset;
> }
>
> @@ -117,11 +117,12 @@ static void build_check_ruleset(void)
> .num_rules = ~0,
> .num_layers = ~0,
> };
> - typeof(ruleset.fs_access_masks[0]) fs_access_mask = ~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(fs_access_mask < LANDLOCK_MASK_ACCESS_FS);
> + BUILD_BUG_ON(access_masks <
> + (LANDLOCK_MASK_ACCESS_FS << LANDLOCK_SHIFT_ACCESS_FS));
> }
>
> /**
> @@ -281,7 +282,7 @@ static int merge_ruleset(struct landlock_ruleset *const dst,
> err = -EINVAL;
> goto out_unlock;
> }
> - dst->fs_access_masks[dst->num_layers - 1] = src->fs_access_masks[0];
> + dst->access_masks[dst->num_layers - 1] = src->access_masks[0];
>
> /* Merges the @src tree. */
> rbtree_postorder_for_each_entry_safe(walker_rule, next_rule, &src->root,
> @@ -340,8 +341,8 @@ static int inherit_ruleset(struct landlock_ruleset *const parent,
> goto out_unlock;
> }
> /* Copies the parent layer stack and leaves a space for the new layer. */
> - memcpy(child->fs_access_masks, parent->fs_access_masks,
> - flex_array_size(parent, fs_access_masks, parent->num_layers));
> + memcpy(child->access_masks, parent->access_masks,
> + flex_array_size(parent, access_masks, parent->num_layers));
>
> if (WARN_ON_ONCE(!parent->hierarchy)) {
> err = -EINVAL;
> diff --git a/security/landlock/ruleset.h b/security/landlock/ruleset.h
> index d43231b783e4..f2ad932d396c 100644
> --- a/security/landlock/ruleset.h
> +++ b/security/landlock/ruleset.h
> @@ -25,6 +25,11 @@ static_assert(BITS_PER_TYPE(access_mask_t) >= LANDLOCK_NUM_ACCESS_FS);
> /* Makes sure for_each_set_bit() and for_each_clear_bit() calls are OK. */
> static_assert(sizeof(unsigned long) >= sizeof(access_mask_t));
>
> +/* Ruleset access masks. */
> +typedef u16 access_masks_t;
> +/* Makes sure all ruleset access rights can be stored. */
> +static_assert(BITS_PER_TYPE(access_masks_t) >= LANDLOCK_NUM_ACCESS_FS);
> +
> typedef u16 layer_mask_t;
> /* Makes sure all layers can be checked. */
> static_assert(BITS_PER_TYPE(layer_mask_t) >= LANDLOCK_MAX_NUM_LAYERS);
> @@ -110,7 +115,7 @@ struct landlock_ruleset {
> * section. This is only used by
> * landlock_put_ruleset_deferred() when @usage reaches zero.
> * The fields @lock, @usage, @num_rules, @num_layers and
> - * @fs_access_masks are then unused.
> + * @access_masks are then unused.
> */
> struct work_struct work_free;
> struct {
> @@ -137,7 +142,7 @@ struct landlock_ruleset {
> */
> u32 num_layers;
> /**
> - * @fs_access_masks: Contains the subset of filesystem
> + * @access_masks: Contains the subset of filesystem
> * actions that are restricted by a ruleset. A domain
> * saves all layers of merged rulesets in a stack
> * (FAM), starting from the first layer to the last
> @@ -148,13 +153,13 @@ struct landlock_ruleset {
> * layers are set once and never changed for the
> * lifetime of the ruleset.
> */
> - access_mask_t fs_access_masks[];
> + access_masks_t access_masks[];
> };
> };
> };
>
> struct landlock_ruleset *
> -landlock_create_ruleset(const access_mask_t fs_access_mask);
> +landlock_create_ruleset(const access_mask_t access_mask);
>
> void landlock_put_ruleset(struct landlock_ruleset *const ruleset);
> void landlock_put_ruleset_deferred(struct landlock_ruleset *const ruleset);
> @@ -177,4 +182,26 @@ static inline void landlock_get_ruleset(struct landlock_ruleset *const ruleset)
> refcount_inc(&ruleset->usage);
> }
>
> +static inline void
> +landlock_add_fs_access_mask(struct landlock_ruleset *const ruleset,
> + const access_mask_t fs_access_mask,
> + const u16 layer_level)
> +{
> + access_mask_t fs_mask = fs_access_mask & LANDLOCK_MASK_ACCESS_FS;
> +
> + /* Should already be checked in sys_landlock_create_ruleset(). */
> + WARN_ON_ONCE(fs_access_mask != fs_mask);
> + // TODO: Add tests to check "|=" and not "="
This todo should be done and removed. No more todos must remain.
> + ruleset->access_masks[layer_level] |=
> + (fs_mask << LANDLOCK_SHIFT_ACCESS_FS);
> +}
> +
> +static inline access_mask_t
> +landlock_get_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;
> +}
> #endif /* _SECURITY_LANDLOCK_RULESET_H */
> diff --git a/security/landlock/syscalls.c b/security/landlock/syscalls.c
> index 245cc650a4dc..71aca7f990bc 100644
> --- a/security/landlock/syscalls.c
> +++ b/security/landlock/syscalls.c
> @@ -346,10 +346,11 @@ SYSCALL_DEFINE4(landlock_add_rule, const int, ruleset_fd,
> }
> /*
> * Checks that allowed_access matches the @ruleset constraints
> - * (ruleset->fs_access_masks[0] is automatically upgraded to 64-bits).
> + * (ruleset->access_masks[0] is automatically upgraded to 64-bits).
> */
> - if ((path_beneath_attr.allowed_access | ruleset->fs_access_masks[0]) !=
> - ruleset->fs_access_masks[0]) {
> + if ((path_beneath_attr.allowed_access |
> + landlock_get_fs_access_mask(ruleset, 0)) !=
> + landlock_get_fs_access_mask(ruleset, 0)) {
> err = -EINVAL;
> goto out_put_ruleset;
> }
> --
> 2.25.1
>
I'll send a patch to be applied after this one.
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