[PATCH] landlock: Allow filesystem layout changes for domains without such rule type
Konstantin Meskhidze (A)
konstantin.meskhidze at huawei.com
Mon Nov 28 03:04:18 UTC 2022
11/18/2022 12:16 PM, Mickaël Salaün пишет:
> 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.
> Do you have this patch online? Can I fetch it from your repo?
>
> 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 at digikod.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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