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Message-ID: <fb9a288a-aa86-9192-e6d7-d6678d740297@digikod.net>
Date: Fri, 18 Nov 2022 10:16:21 +0100
From: Mickaël Salaün <mic@...ikod.net>
To: Konstantin Meskhidze <konstantin.meskhidze@...wei.com>
Cc: artem.kuzin@...wei.com, gnoack3000@...il.com,
willemdebruijn.kernel@...il.com,
linux-security-module@...r.kernel.org, netdev@...r.kernel.org,
netfilter-devel@...r.kernel.org
Subject: Re: [PATCH] landlock: Allow filesystem layout changes for domains
without such rule type
Konstantin, this patch should apply cleanly just after "01/12 landlock:
Make ruleset's access masks more generic". You can easily get this patch
with https://git.kernel.org/pub/scm/utils/b4/b4.git/
Some adjustments are needed for the following patches. Feel free to
review this patch.
On 17/11/2022 19:55, Mickaël Salaün wrote:
> Allow mount point and root directory changes when there is no filesystem
> rule tied to the current Landlock domain. This doesn't change anything
> for now because a domain must have at least a (filesystem) rule, but
> this will change when other rule types will come. For instance, a
> domain only restricting the network should have no impact on filesystem
> restrictions.
>
> Add a new get_current_fs_domain() helper to quickly check filesystem
> rule existence for all filesystem LSM hooks.
>
> Remove unnecessary inlining.
>
> Signed-off-by: Mickaël Salaün <mic@...ikod.net>
> ---
> security/landlock/fs.c | 73 ++++++++++++++++++------------------
> security/landlock/ruleset.h | 25 +++++++++++-
> security/landlock/syscalls.c | 6 +--
> 3 files changed, 62 insertions(+), 42 deletions(-)
>
> diff --git a/security/landlock/fs.c b/security/landlock/fs.c
> index 0d57c6479d29..0ae54a639e16 100644
> --- a/security/landlock/fs.c
> +++ b/security/landlock/fs.c
> @@ -150,16 +150,6 @@ static struct landlock_object *get_inode_object(struct inode *const inode)
> LANDLOCK_ACCESS_FS_TRUNCATE)
> /* clang-format on */
>
> -/*
> - * All access rights that are denied by default whether they are handled or not
> - * by a ruleset/layer. This must be ORed with all ruleset->fs_access_masks[]
> - * entries when we need to get the absolute handled access masks.
> - */
> -/* clang-format off */
> -#define ACCESS_INITIALLY_DENIED ( \
> - LANDLOCK_ACCESS_FS_REFER)
> -/* clang-format on */
> -
> /*
> * @path: Should have been checked by get_path_from_fd().
> */
> @@ -179,8 +169,7 @@ int landlock_append_fs_rule(struct landlock_ruleset *const ruleset,
>
> /* Transforms relative access rights to absolute ones. */
> access_rights |= LANDLOCK_MASK_ACCESS_FS &
> - ~(landlock_get_fs_access_mask(ruleset, 0) |
> - ACCESS_INITIALLY_DENIED);
> + ~landlock_get_fs_access_mask(ruleset, 0);
> object = get_inode_object(d_backing_inode(path->dentry));
> if (IS_ERR(object))
> return PTR_ERR(object);
> @@ -287,14 +276,15 @@ static inline bool is_nouser_or_private(const struct dentry *dentry)
> unlikely(IS_PRIVATE(d_backing_inode(dentry))));
> }
>
> -static inline access_mask_t
> -get_handled_accesses(const struct landlock_ruleset *const domain)
> +static access_mask_t
> +get_raw_handled_fs_accesses(const struct landlock_ruleset *const domain)
> {
> - access_mask_t access_dom = ACCESS_INITIALLY_DENIED;
> + 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_fs_access_mask(domain, layer_level);
> + access_dom |=
> + landlock_get_raw_fs_access_mask(domain, layer_level);
> return access_dom & LANDLOCK_MASK_ACCESS_FS;
> }
>
> @@ -331,13 +321,8 @@ init_layer_masks(const struct landlock_ruleset *const domain,
>
> for_each_set_bit(access_bit, &access_req,
> ARRAY_SIZE(*layer_masks)) {
> - /*
> - * Artificially handles all initially denied by default
> - * access rights.
> - */
> if (BIT_ULL(access_bit) &
> - (landlock_get_fs_access_mask(domain, layer_level) |
> - ACCESS_INITIALLY_DENIED)) {
> + landlock_get_fs_access_mask(domain, layer_level)) {
> (*layer_masks)[access_bit] |=
> BIT_ULL(layer_level);
> handled_accesses |= BIT_ULL(access_bit);
> @@ -347,6 +332,24 @@ init_layer_masks(const struct landlock_ruleset *const domain,
> return handled_accesses;
> }
>
> +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) | ACCESS_FS_INITIALLY_DENIED;
> +}
> +
> +static const struct landlock_ruleset *get_current_fs_domain(void)
> +{
> + const struct landlock_ruleset *const dom =
> + landlock_get_current_domain();
> +
> + if (!dom || !get_raw_handled_fs_accesses(dom))
> + return NULL;
> +
> + return dom;
> +}
> +
> /*
> * Check that a destination file hierarchy has more restrictions than a source
> * file hierarchy. This is only used for link and rename actions.
> @@ -519,7 +522,7 @@ static bool is_access_to_paths_allowed(
> * a superset of the meaningful requested accesses).
> */
> access_masked_parent1 = access_masked_parent2 =
> - get_handled_accesses(domain);
> + get_handled_fs_accesses(domain);
> is_dom_check = true;
> } else {
> if (WARN_ON_ONCE(dentry_child1 || dentry_child2))
> @@ -648,11 +651,10 @@ static inline int check_access_path(const struct landlock_ruleset *const domain,
> return -EACCES;
> }
>
> -static inline int current_check_access_path(const struct path *const path,
> +static int current_check_access_path(const struct path *const path,
> const access_mask_t access_request)
> {
> - const struct landlock_ruleset *const dom =
> - landlock_get_current_domain();
> + const struct landlock_ruleset *const dom = get_current_fs_domain();
>
> if (!dom)
> return 0;
> @@ -815,8 +817,7 @@ static int current_check_refer_path(struct dentry *const old_dentry,
> struct dentry *const new_dentry,
> const bool removable, const bool exchange)
> {
> - const struct landlock_ruleset *const dom =
> - landlock_get_current_domain();
> + const struct landlock_ruleset *const dom = get_current_fs_domain();
> bool allow_parent1, allow_parent2;
> access_mask_t access_request_parent1, access_request_parent2;
> struct path mnt_dir;
> @@ -1050,7 +1051,7 @@ static int hook_sb_mount(const char *const dev_name,
> const struct path *const path, const char *const type,
> const unsigned long flags, void *const data)
> {
> - if (!landlock_get_current_domain())
> + if (!get_current_fs_domain())
> return 0;
> return -EPERM;
> }
> @@ -1058,7 +1059,7 @@ static int hook_sb_mount(const char *const dev_name,
> static int hook_move_mount(const struct path *const from_path,
> const struct path *const to_path)
> {
> - if (!landlock_get_current_domain())
> + if (!get_current_fs_domain())
> return 0;
> return -EPERM;
> }
> @@ -1069,14 +1070,14 @@ static int hook_move_mount(const struct path *const from_path,
> */
> static int hook_sb_umount(struct vfsmount *const mnt, const int flags)
> {
> - if (!landlock_get_current_domain())
> + if (!get_current_fs_domain())
> return 0;
> return -EPERM;
> }
>
> static int hook_sb_remount(struct super_block *const sb, void *const mnt_opts)
> {
> - if (!landlock_get_current_domain())
> + if (!get_current_fs_domain())
> return 0;
> return -EPERM;
> }
> @@ -1092,7 +1093,7 @@ static int hook_sb_remount(struct super_block *const sb, void *const mnt_opts)
> static int hook_sb_pivotroot(const struct path *const old_path,
> const struct path *const new_path)
> {
> - if (!landlock_get_current_domain())
> + if (!get_current_fs_domain())
> return 0;
> return -EPERM;
> }
> @@ -1128,8 +1129,7 @@ static int hook_path_mknod(const struct path *const dir,
> struct dentry *const dentry, const umode_t mode,
> const unsigned int dev)
> {
> - const struct landlock_ruleset *const dom =
> - landlock_get_current_domain();
> + const struct landlock_ruleset *const dom = get_current_fs_domain();
>
> if (!dom)
> return 0;
> @@ -1208,8 +1208,7 @@ 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;
> const access_mask_t optional_access = LANDLOCK_ACCESS_FS_TRUNCATE;
> - const struct landlock_ruleset *const dom =
> - landlock_get_current_domain();
> + const struct landlock_ruleset *const dom = get_current_fs_domain();
>
> if (!dom)
> return 0;
> diff --git a/security/landlock/ruleset.h b/security/landlock/ruleset.h
> index f2ad932d396c..ca46393ef3bb 100644
> --- a/security/landlock/ruleset.h
> +++ b/security/landlock/ruleset.h
> @@ -15,10 +15,21 @@
> #include <linux/rbtree.h>
> #include <linux/refcount.h>
> #include <linux/workqueue.h>
> +#include <uapi/linux/landlock.h>
>
> #include "limits.h"
> #include "object.h"
>
> +/*
> + * All access rights that are denied by default whether they are handled or not
> + * by a ruleset/layer. This must be ORed with all ruleset->access_masks[]
> + * entries when we need to get the absolute handled access masks.
> + */
> +/* clang-format off */
> +#define ACCESS_FS_INITIALLY_DENIED ( \
> + LANDLOCK_ACCESS_FS_REFER)
> +/* clang-format on */
> +
> typedef u16 access_mask_t;
> /* Makes sure all filesystem access rights can be stored. */
> static_assert(BITS_PER_TYPE(access_mask_t) >= LANDLOCK_NUM_ACCESS_FS);
> @@ -197,11 +208,21 @@ landlock_add_fs_access_mask(struct landlock_ruleset *const ruleset,
> }
>
> static inline access_mask_t
> -landlock_get_fs_access_mask(const struct landlock_ruleset *const ruleset,
> - const u16 layer_level)
> +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;
> }
> +
> +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) |
> + ACCESS_FS_INITIALLY_DENIED;
> +}
> +
> #endif /* _SECURITY_LANDLOCK_RULESET_H */
> diff --git a/security/landlock/syscalls.c b/security/landlock/syscalls.c
> index 71aca7f990bc..d35cd5d304db 100644
> --- a/security/landlock/syscalls.c
> +++ b/security/landlock/syscalls.c
> @@ -310,6 +310,7 @@ SYSCALL_DEFINE4(landlock_add_rule, const int, ruleset_fd,
> struct path path;
> struct landlock_ruleset *ruleset;
> int res, err;
> + access_mask_t mask;
>
> if (!landlock_initialized)
> return -EOPNOTSUPP;
> @@ -348,9 +349,8 @@ SYSCALL_DEFINE4(landlock_add_rule, const int, ruleset_fd,
> * Checks that allowed_access matches the @ruleset constraints
> * (ruleset->access_masks[0] is automatically upgraded to 64-bits).
> */
> - if ((path_beneath_attr.allowed_access |
> - landlock_get_fs_access_mask(ruleset, 0)) !=
> - landlock_get_fs_access_mask(ruleset, 0)) {
> + mask = landlock_get_raw_fs_access_mask(ruleset, 0);
> + if ((path_beneath_attr.allowed_access | mask) != mask) {
> err = -EINVAL;
> goto out_put_ruleset;
> }
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