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Fix and improve documentation related to landlock_restrict_self(2)'s
flags. Update the LANDLOCK_RESTRICT_SELF_LOG_SAME_EXEC_OFF
documentation according to the current semantic.
Cc: Günther Noack <gnoack@google.com>
Cc: Paul Moore <paul@paul-moore.com>
Link: https://lore.kernel.org/r/20250416154716.1799902-3-mic@digikod.net
Signed-off-by: Mickaël Salaün <mic@digikod.net>
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Fix, deduplicate, and improve rendering of landlock_restrict_self(2)'s
flags documentation.
The flags are now rendered like the syscall's parameters and
description.
Cc: Günther Noack <gnoack@google.com>
Cc: Paul Moore <paul@paul-moore.com>
Link: https://lore.kernel.org/r/20250416154716.1799902-2-mic@digikod.net
Signed-off-by: Mickaël Salaün <mic@digikod.net>
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Move and fix the flags documentation, and improve formatting.
It makes more sense and it eases maintenance to document syscall flags
in landlock.h, where they are defined. This is already the case for
landlock_restrict_self(2)'s flags.
The flags are now rendered like the syscall's parameters and
description.
Cc: Günther Noack <gnoack@google.com>
Cc: Paul Moore <paul@paul-moore.com>
Link: https://lore.kernel.org/r/20250416154716.1799902-1-mic@digikod.net
Signed-off-by: Mickaël Salaün <mic@digikod.net>
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Add LANDLOCK_RESTRICT_SELF_LOG_SUBDOMAINS_OFF for the case of sandboxer
tools, init systems, or runtime containers launching programs sandboxing
themselves in an inconsistent way. Setting this flag should only
depends on runtime configuration (i.e. not hardcoded).
We don't create a new ruleset's option because this should not be part
of the security policy: only the task that enforces the policy (not the
one that create it) knows if itself or its children may request denied
actions.
This is the first and only flag that can be set without actually
restricting the caller (i.e. without providing a ruleset).
Extend struct landlock_cred_security with a u8 log_subdomains_off.
struct landlock_file_security is still 16 bytes.
Cc: Günther Noack <gnoack@google.com>
Cc: Paul Moore <paul@paul-moore.com>
Closes: https://github.com/landlock-lsm/linux/issues/3
Link: https://lore.kernel.org/r/20250320190717.2287696-19-mic@digikod.net
[mic: Fix comment]
Signed-off-by: Mickaël Salaün <mic@digikod.net>
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Most of the time we want to log denied access because they should not
happen and such information helps diagnose issues. However, when
sandboxing processes that we know will try to access denied resources
(e.g. unknown, bogus, or malicious binary), we might want to not log
related access requests that might fill up logs.
By default, denied requests are logged until the task call execve(2).
If the LANDLOCK_RESTRICT_SELF_LOG_SAME_EXEC_OFF flag is set, denied
requests will not be logged for the same executed file.
If the LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON flag is set, denied
requests from after an execve(2) call will be logged.
The rationale is that a program should know its own behavior, but not
necessarily the behavior of other programs.
Because LANDLOCK_RESTRICT_SELF_LOG_SAME_EXEC_OFF is set for a specific
Landlock domain, it makes it possible to selectively mask some access
requests that would be logged by a parent domain, which might be handy
for unprivileged processes to limit logs. However, system
administrators should still use the audit filtering mechanism. There is
intentionally no audit nor sysctl configuration to re-enable these logs.
This is delegated to the user space program.
Increment the Landlock ABI version to reflect this interface change.
Cc: Günther Noack <gnoack@google.com>
Cc: Paul Moore <paul@paul-moore.com>
Link: https://lore.kernel.org/r/20250320190717.2287696-18-mic@digikod.net
[mic: Rename variables and fix __maybe_unused]
Signed-off-by: Mickaël Salaün <mic@digikod.net>
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Some fixes may require user space to check if they are applied on the
running kernel before using a specific feature. For instance, this
applies when a restriction was previously too restrictive and is now
getting relaxed (e.g. for compatibility reasons). However, non-visible
changes for legitimate use (e.g. security fixes) do not require an
erratum.
Because fixes are backported down to a specific Landlock ABI, we need a
way to avoid cherry-pick conflicts. The solution is to only update a
file related to the lower ABI impacted by this issue. All the ABI files
are then used to create a bitmask of fixes.
The new errata interface is similar to the one used to get the supported
Landlock ABI version, but it returns a bitmask instead because the order
of fixes may not match the order of versions, and not all fixes may
apply to all versions.
The actual errata will come with dedicated commits. The description is
not actually used in the code but serves as documentation.
Create the landlock_abi_version symbol and use its value to check errata
consistency.
Update test_base's create_ruleset_checks_ordering tests and add errata
tests.
This commit is backportable down to the first version of Landlock.
Fixes: 3532b0b4352c ("landlock: Enable user space to infer supported features")
Cc: Günther Noack <gnoack@google.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20250318161443.279194-3-mic@digikod.net
Signed-off-by: Mickaël Salaün <mic@digikod.net>
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* Fix some whitespace, punctuation and minor grammar.
* Add a missing sentence about the minimum ABI version,
to stay in line with the section next to it.
Cc: Tahera Fahimi <fahimitahera@gmail.com>
Cc: Tanya Agarwal <tanyaagarwal25699@gmail.com>
Signed-off-by: Günther Noack <gnoack@google.com>
Link: https://lore.kernel.org/r/20250124154445.162841-1-gnoack@google.com
[mic: Add newlines, update doc date]
Signed-off-by: Mickaël Salaün <mic@digikod.net>
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Currently, a sandbox process is not restricted to sending a signal (e.g.
SIGKILL) to a process outside the sandbox environment. The ability to
send a signal for a sandboxed process should be scoped the same way
abstract UNIX sockets are scoped. Therefore, we extend the "scoped"
field in a ruleset with LANDLOCK_SCOPE_SIGNAL to specify that a ruleset
will deny sending any signal from within a sandbox process to its parent
(i.e. any parent sandbox or non-sandboxed processes).
This patch adds file_set_fowner and file_free_security hooks to set and
release a pointer to the file owner's domain. This pointer, fown_domain
in landlock_file_security will be used in file_send_sigiotask to check
if the process can send a signal.
The ruleset_with_unknown_scope test is updated to support
LANDLOCK_SCOPE_SIGNAL.
This depends on two new changes:
- commit 1934b212615d ("file: reclaim 24 bytes from f_owner"): replace
container_of(fown, struct file, f_owner) with fown->file .
- commit 26f204380a3c ("fs: Fix file_set_fowner LSM hook
inconsistencies"): lock before calling the hook.
Signed-off-by: Tahera Fahimi <fahimitahera@gmail.com>
Closes: https://github.com/landlock-lsm/linux/issues/8
Link: https://lore.kernel.org/r/df2b4f880a2ed3042992689a793ea0951f6798a5.1725657727.git.fahimitahera@gmail.com
[mic: Update landlock_get_current_domain()'s return type, improve and
fix locking in hook_file_set_fowner(), simplify and fix sleepable call
and locking issue in hook_file_send_sigiotask() and rebase on the latest
VFS tree, simplify hook_task_kill() and quickly return when not
sandboxed, improve comments, rename LANDLOCK_SCOPED_SIGNAL]
Co-developed-by: Mickaël Salaün <mic@digikod.net>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
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Introduce a new "scoped" member to landlock_ruleset_attr that can
specify LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET to restrict connection to
abstract UNIX sockets from a process outside of the socket's domain.
Two hooks are implemented to enforce these restrictions:
unix_stream_connect and unix_may_send.
Closes: https://github.com/landlock-lsm/linux/issues/7
Signed-off-by: Tahera Fahimi <fahimitahera@gmail.com>
Link: https://lore.kernel.org/r/5f7ad85243b78427242275b93481cfc7c127764b.1725494372.git.fahimitahera@gmail.com
[mic: Fix commit message formatting, improve documentation, simplify
hook_unix_may_send(), and cosmetic fixes including rename of
LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET]
Co-developed-by: Mickaël Salaün <mic@digikod.net>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
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* Fix some typos, incomplete or confusing phrases.
* Split paragraphs where appropriate.
* List the same error code multiple times,
if it has multiple possible causes.
* Bring wording closer to the man page wording,
which has undergone more thorough review
(esp. for LANDLOCK_ACCESS_FS_WRITE_FILE).
* Small semantic clarifications
* Call the ephemeral port range "ephemeral"
* Clarify reasons for EFAULT in landlock_add_rule()
* Clarify @rule_type doc for landlock_add_rule()
This is a collection of small fixes which I collected when preparing the
corresponding man pages [1].
Cc: Alejandro Colomar <alx@kernel.org>
Cc: Konstantin Meskhidze <konstantin.meskhidze@huawei.com>
Link: https://lore.kernel.org/r/20240715155554.2791018-1-gnoack@google.com [1]
Signed-off-by: Günther Noack <gnoack@google.com>
Link: https://lore.kernel.org/r/20240715160328.2792835-2-gnoack@google.com
[mic: Add label to link, fix formatting spotted by make htmldocs,
synchronize userspace-api documentation's date]
Signed-off-by: Mickaël Salaün <mic@digikod.net>
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The explanation for @handled_access_fs and @handled_access_net has
significant overlap and is better explained together.
* Explain the commonalities in structure-level documentation.
* Clarify some wording and break up longer sentences.
* Put emphasis on the word "handled" to make it clearer that "handled"
is a term with special meaning in the context of Landlock.
I'd like to transfer this wording into the man pages as well.
Signed-off-by: Günther Noack <gnoack@google.com>
Cc: Alejandro Colomar <alx@kernel.org>
Cc: Konstantin Meskhidze <konstantin.meskhidze@huawei.com>
Cc: linux-security-module@vger.kernel.org
Link: https://lore.kernel.org/r/20240711165456.2148590-2-gnoack@google.com
[mic: Format commit message]
Signed-off-by: Mickaël Salaün <mic@digikod.net>
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Introduces the LANDLOCK_ACCESS_FS_IOCTL_DEV right
and increments the Landlock ABI version to 5.
This access right applies to device-custom IOCTL commands
when they are invoked on block or character device files.
Like the truncate right, this right is associated with a file
descriptor at the time of open(2), and gets respected even when the
file descriptor is used outside of the thread which it was originally
opened in.
Therefore, a newly enabled Landlock policy does not apply to file
descriptors which are already open.
If the LANDLOCK_ACCESS_FS_IOCTL_DEV right is handled, only a small
number of safe IOCTL commands will be permitted on newly opened device
files. These include FIOCLEX, FIONCLEX, FIONBIO and FIOASYNC, as well
as other IOCTL commands for regular files which are implemented in
fs/ioctl.c.
Noteworthy scenarios which require special attention:
TTY devices are often passed into a process from the parent process,
and so a newly enabled Landlock policy does not retroactively apply to
them automatically. In the past, TTY devices have often supported
IOCTL commands like TIOCSTI and some TIOCLINUX subcommands, which were
letting callers control the TTY input buffer (and simulate
keypresses). This should be restricted to CAP_SYS_ADMIN programs on
modern kernels though.
Known limitations:
The LANDLOCK_ACCESS_FS_IOCTL_DEV access right is a coarse-grained
control over IOCTL commands.
Landlock users may use path-based restrictions in combination with
their knowledge about the file system layout to control what IOCTLs
can be done.
Cc: Paul Moore <paul@paul-moore.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Günther Noack <gnoack@google.com>
Link: https://lore.kernel.org/r/20240419161122.2023765-2-gnoack@google.com
Signed-off-by: Mickaël Salaün <mic@digikod.net>
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Add network rules support in the ruleset management helpers and the
landlock_create_ruleset() syscall. Extend user space API to support
network actions:
* Add new network access rights: LANDLOCK_ACCESS_NET_BIND_TCP and
LANDLOCK_ACCESS_NET_CONNECT_TCP.
* Add a new network rule type: LANDLOCK_RULE_NET_PORT tied to struct
landlock_net_port_attr. The allowed_access field contains the network
access rights, and the port field contains the port value according to
the controlled protocol. This field can take up to a 64-bit value
but the maximum value depends on the related protocol (e.g. 16-bit
value for TCP). Network port is in host endianness [1].
* Add a new handled_access_net field to struct landlock_ruleset_attr
that contains network access rights.
* Increment the Landlock ABI version to 4.
Implement socket_bind() and socket_connect() LSM hooks, which enable
to control TCP socket binding and connection to specific ports.
Expand access_masks_t from u16 to u32 to be able to store network access
rights alongside filesystem access rights for rulesets' handled access
rights.
Access rights are not tied to socket file descriptors but checked at
bind() or connect() call time against the caller's Landlock domain. For
the filesystem, a file descriptor is a direct access to a file/data.
However, for network sockets, we cannot identify for which data or peer
a newly created socket will give access to. Indeed, we need to wait for
a connect or bind request to identify the use case for this socket.
Likewise a directory file descriptor may enable to open another file
(i.e. a new data item), but this opening is also restricted by the
caller's domain, not the file descriptor's access rights [2].
[1] https://lore.kernel.org/r/278ab07f-7583-a4e0-3d37-1bacd091531d@digikod.net
[2] https://lore.kernel.org/r/263c1eb3-602f-57fe-8450-3f138581bee7@digikod.net
Signed-off-by: Konstantin Meskhidze <konstantin.meskhidze@huawei.com>
Link: https://lore.kernel.org/r/20231026014751.414649-9-konstantin.meskhidze@huawei.com
[mic: Extend commit message, fix typo in comments, and specify
endianness in the documentation]
Co-developed-by: Mickaël Salaün <mic@digikod.net>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
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Clarify the "refer" documentation by splitting up a big paragraph of
text.
- Call out specifically that the denial by default applies to ABI v1 as
well.
- Turn the three additional constraints for link/rename operations
into bullet points, to give it more structure.
Signed-off-by: Günther Noack <gnoack3000@gmail.com>
Link: https://lore.kernel.org/r/20230221165205.4231-1-gnoack3000@gmail.com
Signed-off-by: Mickaël Salaün <mic@digikod.net>
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Introduce the LANDLOCK_ACCESS_FS_TRUNCATE flag for file truncation.
This flag hooks into the path_truncate, file_truncate and
file_alloc_security LSM hooks and covers file truncation using
truncate(2), ftruncate(2), open(2) with O_TRUNC, as well as creat().
This change also increments the Landlock ABI version, updates
corresponding selftests, and updates code documentation to document
the flag.
In security/security.c, allocate security blobs at pointer-aligned
offsets. This fixes the problem where one LSM's security blob can
shift another LSM's security blob to an unaligned address (reported
by Nathan Chancellor).
The following operations are restricted:
open(2): requires the LANDLOCK_ACCESS_FS_TRUNCATE right if a file gets
implicitly truncated as part of the open() (e.g. using O_TRUNC).
Notable special cases:
* open(..., O_RDONLY|O_TRUNC) can truncate files as well in Linux
* open() with O_TRUNC does *not* need the TRUNCATE right when it
creates a new file.
truncate(2) (on a path): requires the LANDLOCK_ACCESS_FS_TRUNCATE
right.
ftruncate(2) (on a file): requires that the file had the TRUNCATE
right when it was previously opened. File descriptors acquired by
other means than open(2) (e.g. memfd_create(2)) continue to support
truncation with ftruncate(2).
Cc: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Günther Noack <gnoack3000@gmail.com>
Acked-by: Paul Moore <paul@paul-moore.com> (LSM)
Link: https://lore.kernel.org/r/20221018182216.301684-5-gnoack3000@gmail.com
Signed-off-by: Mickaël Salaün <mic@digikod.net>
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It seems that all code should use double backquotes, which is also used
to convert "%" defines. Let's use an homogeneous style and remove all
use of simple backquotes (which should only be used for emphasis).
Cc: Günther Noack <gnoack3000@gmail.com>
Cc: Paul Moore <paul@paul-moore.com>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20220923154207.3311629-4-mic@digikod.net
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Add a new LANDLOCK_ACCESS_FS_REFER access right to enable policy writers
to allow sandboxed processes to link and rename files from and to a
specific set of file hierarchies. This access right should be composed
with LANDLOCK_ACCESS_FS_MAKE_* for the destination of a link or rename,
and with LANDLOCK_ACCESS_FS_REMOVE_* for a source of a rename. This
lift a Landlock limitation that always denied changing the parent of an
inode.
Renaming or linking to the same directory is still always allowed,
whatever LANDLOCK_ACCESS_FS_REFER is used or not, because it is not
considered a threat to user data.
However, creating multiple links or renaming to a different parent
directory may lead to privilege escalations if not handled properly.
Indeed, we must be sure that the source doesn't gain more privileges by
being accessible from the destination. This is handled by making sure
that the source hierarchy (including the referenced file or directory
itself) restricts at least as much the destination hierarchy. If it is
not the case, an EXDEV error is returned, making it potentially possible
for user space to copy the file hierarchy instead of moving or linking
it.
Instead of creating different access rights for the source and the
destination, we choose to make it simple and consistent for users.
Indeed, considering the previous constraint, it would be weird to
require such destination access right to be also granted to the source
(to make it a superset). Moreover, RENAME_EXCHANGE would also add to
the confusion because of paths being both a source and a destination.
See the provided documentation for additional details.
New tests are provided with a following commit.
Reviewed-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20220506161102.525323-8-mic@digikod.net
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It is not mandatory to pass a file descriptor obtained with the O_PATH
flag. Also, replace rule's accesses with ruleset's accesses.
Link: https://lore.kernel.org/r/20220506160820.524344-2-mic@digikod.net
Cc: stable@vger.kernel.org
Signed-off-by: Mickaël Salaün <mic@digikod.net>
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In preparation to a following commit, add clang-format on and
clang-format off stanzas around constant definitions. This enables to
keep aligned values, which is much more readable than packed
definitions.
Link: https://lore.kernel.org/r/20220506160513.523257-2-mic@digikod.net
Cc: stable@vger.kernel.org
Signed-off-by: Mickaël Salaün <mic@digikod.net>
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Add a new flag LANDLOCK_CREATE_RULESET_VERSION to
landlock_create_ruleset(2). This enables to retreive a Landlock ABI
version that is useful to efficiently follow a best-effort security
approach. Indeed, it would be a missed opportunity to abort the whole
sandbox building, because some features are unavailable, instead of
protecting users as much as possible with the subset of features
provided by the running kernel.
This new flag enables user space to identify the minimum set of Landlock
features supported by the running kernel without relying on a filesystem
interface (e.g. /proc/version, which might be inaccessible) nor testing
multiple syscall argument combinations (i.e. syscall bisection). New
Landlock features will be documented and tied to a minimum version
number (greater than 1). The current version will be incremented for
each new kernel release supporting new Landlock features. User space
libraries can leverage this information to seamlessly restrict processes
as much as possible while being compatible with newer APIs.
This is a much more lighter approach than the previous
landlock_get_features(2): the complexity is pushed to user space
libraries. This flag meets similar needs as securityfs versions:
selinux/policyvers, apparmor/features/*/version* and tomoyo/version.
Supporting this flag now will be convenient for backward compatibility.
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: James Morris <jmorris@namei.org>
Cc: Jann Horn <jannh@google.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Serge E. Hallyn <serge@hallyn.com>
Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com>
Link: https://lore.kernel.org/r/20210422154123.13086-14-mic@digikod.net
Signed-off-by: James Morris <jamorris@linux.microsoft.com>
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These 3 system calls are designed to be used by unprivileged processes
to sandbox themselves:
* landlock_create_ruleset(2): Creates a ruleset and returns its file
descriptor.
* landlock_add_rule(2): Adds a rule (e.g. file hierarchy access) to a
ruleset, identified by the dedicated file descriptor.
* landlock_restrict_self(2): Enforces a ruleset on the calling thread
and its future children (similar to seccomp). This syscall has the
same usage restrictions as seccomp(2): the caller must have the
no_new_privs attribute set or have CAP_SYS_ADMIN in the current user
namespace.
All these syscalls have a "flags" argument (not currently used) to
enable extensibility.
Here are the motivations for these new syscalls:
* A sandboxed process may not have access to file systems, including
/dev, /sys or /proc, but it should still be able to add more
restrictions to itself.
* Neither prctl(2) nor seccomp(2) (which was used in a previous version)
fit well with the current definition of a Landlock security policy.
All passed structs (attributes) are checked at build time to ensure that
they don't contain holes and that they are aligned the same way for each
architecture.
See the user and kernel documentation for more details (provided by a
following commit):
* Documentation/userspace-api/landlock.rst
* Documentation/security/landlock.rst
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: James Morris <jmorris@namei.org>
Cc: Jann Horn <jannh@google.com>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com>
Acked-by: Serge Hallyn <serge@hallyn.com>
Link: https://lore.kernel.org/r/20210422154123.13086-9-mic@digikod.net
Signed-off-by: James Morris <jamorris@linux.microsoft.com>
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Using Landlock objects and ruleset, it is possible to tag inodes
according to a process's domain. To enable an unprivileged process to
express a file hierarchy, it first needs to open a directory (or a file)
and pass this file descriptor to the kernel through
landlock_add_rule(2). When checking if a file access request is
allowed, we walk from the requested dentry to the real root, following
the different mount layers. The access to each "tagged" inodes are
collected according to their rule layer level, and ANDed to create
access to the requested file hierarchy. This makes possible to identify
a lot of files without tagging every inodes nor modifying the
filesystem, while still following the view and understanding the user
has from the filesystem.
Add a new ARCH_EPHEMERAL_INODES for UML because it currently does not
keep the same struct inodes for the same inodes whereas these inodes are
in use.
This commit adds a minimal set of supported filesystem access-control
which doesn't enable to restrict all file-related actions. This is the
result of multiple discussions to minimize the code of Landlock to ease
review. Thanks to the Landlock design, extending this access-control
without breaking user space will not be a problem. Moreover, seccomp
filters can be used to restrict the use of syscall families which may
not be currently handled by Landlock.
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Cc: James Morris <jmorris@namei.org>
Cc: Jann Horn <jannh@google.com>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Richard Weinberger <richard@nod.at>
Cc: Serge E. Hallyn <serge@hallyn.com>
Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com>
Link: https://lore.kernel.org/r/20210422154123.13086-8-mic@digikod.net
Signed-off-by: James Morris <jamorris@linux.microsoft.com>
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