| b9f5ce27 | 18-Oct-2022 |
Günther Noack <gnoack3000@gmail.com> |
landlock: Support file truncation
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 cov
landlock: Support file truncation
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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| 52a13488 | 18-Oct-2022 |
Günther Noack <gnoack3000@gmail.com> |
landlock: Document init_layer_masks() helper
Add kernel-doc to the init_layer_masks() function.
Signed-off-by: Günther Noack <gnoack3000@gmail.com>
Link: https://lore.kernel.org/r/20221018182216.30
landlock: Document init_layer_masks() helper
Add kernel-doc to the init_layer_masks() function.
Signed-off-by: Günther Noack <gnoack3000@gmail.com>
Link: https://lore.kernel.org/r/20221018182216.301684-4-gnoack3000@gmail.com
Signed-off-by: Mickaël Salaün <mic@digikod.net>
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| 2fff00c8 | 23-Sep-2022 |
Mickaël Salaün <mic@digikod.net> |
landlock: Fix documentation style
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 backquo
landlock: Fix documentation style
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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| b91c3e4e | 06-May-2022 |
Mickaël Salaün <mic@digikod.net> |
landlock: Add support for file reparenting with LANDLOCK_ACCESS_FS_REFER
Add a new LANDLOCK_ACCESS_FS_REFER access right to enable policy writers
to allow sandboxed processes to link and rename file
landlock: Add support for file reparenting with LANDLOCK_ACCESS_FS_REFER
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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| 100f59d9 | 06-May-2022 |
Mickaël Salaün <mic@digikod.net> |
LSM: Remove double path_rename hook calls for RENAME_EXCHANGE
In order to be able to identify a file exchange with renameat2(2) and
RENAME_EXCHANGE, which will be useful for Landlock [1], propagate
LSM: Remove double path_rename hook calls for RENAME_EXCHANGE
In order to be able to identify a file exchange with renameat2(2) and
RENAME_EXCHANGE, which will be useful for Landlock [1], propagate the
rename flags to LSMs. This may also improve performance because of the
switch from two set of LSM hook calls to only one, and because LSMs
using this hook may optimize the double check (e.g. only one lock,
reduce the number of path walks).
AppArmor, Landlock and Tomoyo are updated to leverage this change. This
should not change the current behavior (same check order), except
(different level of) speed boosts.
[1] https://lore.kernel.org/r/20220221212522.320243-1-mic@digikod.net
Cc: James Morris <jmorris@namei.org>
Cc: Kentaro Takeda <takedakn@nttdata.co.jp>
Cc: Serge E. Hallyn <serge@hallyn.com>
Acked-by: John Johansen <john.johansen@canonical.com>
Acked-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reviewed-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20220506161102.525323-7-mic@digikod.net
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| 9da82b20 | 06-May-2022 |
Mickaël Salaün <mic@digikod.net> |
landlock: Move filesystem helpers and add a new one
Move the SB_NOUSER and IS_PRIVATE dentry check to a standalone
is_nouser_or_private() helper. This will be useful for a following
commit.
Move g
landlock: Move filesystem helpers and add a new one
Move the SB_NOUSER and IS_PRIVATE dentry check to a standalone
is_nouser_or_private() helper. This will be useful for a following
commit.
Move get_mode_access() and maybe_remove() to make them usable by new
code provided by 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/20220506161102.525323-6-mic@digikod.net
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| 8ba0005f | 06-May-2022 |
Mickaël Salaün <mic@digikod.net> |
landlock: Fix same-layer rule unions
The original behavior was to check if the full set of requested accesses
was allowed by at least a rule of every relevant layer. This didn't
take into account r
landlock: Fix same-layer rule unions
The original behavior was to check if the full set of requested accesses
was allowed by at least a rule of every relevant layer. This didn't
take into account requests for multiple accesses and same-layer rules
allowing the union of these accesses in a complementary way. As a
result, multiple accesses requested on a file hierarchy matching rules
that, together, allowed these accesses, but without a unique rule
allowing all of them, was illegitimately denied. This case should be
rare in practice and it can only be triggered by the path_rename or
file_open hook implementations.
For instance, if, for the same layer, a rule allows execution
beneath /a/b and another rule allows read beneath /a, requesting access
to read and execute at the same time for /a/b should be allowed for this
layer.
This was an inconsistency because the union of same-layer rule accesses
was already allowed if requested once at a time anyway.
This fix changes the way allowed accesses are gathered over a path walk.
To take into account all these rule accesses, we store in a matrix all
layer granting the set of requested accesses, according to the handled
accesses. To avoid heap allocation, we use an array on the stack which
is 2*13 bytes. A following commit bringing the LANDLOCK_ACCESS_FS_REFER
access right will increase this size to reach 112 bytes (2*14*4) in case
of link or rename actions.
Add a new layout1.layer_rule_unions test to check that accesses from
different rules pertaining to the same layer are ORed in a file
hierarchy. Also test that it is not the case for rules from different
layers.
Reviewed-by: Paul Moore <paul@paul-moore.com>
Link: https://lore.kernel.org/r/20220506161102.525323-5-mic@digikod.net
Cc: stable@vger.kernel.org
Signed-off-by: Mickaël Salaün <mic@digikod.net>
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| 2cd7cd6e | 06-May-2022 |
Mickaël Salaün <mic@digikod.net> |
landlock: Create find_rule() from unmask_layers()
This refactoring will be useful in a following commit.
Reviewed-by: Paul Moore <paul@paul-moore.com>
Link: https://lore.kernel.org/r/20220506161102
landlock: Create find_rule() from unmask_layers()
This refactoring will be useful in a following commit.
Reviewed-by: Paul Moore <paul@paul-moore.com>
Link: https://lore.kernel.org/r/20220506161102.525323-4-mic@digikod.net
Cc: stable@vger.kernel.org
Signed-off-by: Mickaël Salaün <mic@digikod.net>
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| 75c542d6 | 06-May-2022 |
Mickaël Salaün <mic@digikod.net> |
landlock: Reduce the maximum number of layers to 16
The maximum number of nested Landlock domains is currently 64. Because
of the following fix and to help reduce the stack size, let's reduce it
to
landlock: Reduce the maximum number of layers to 16
The maximum number of nested Landlock domains is currently 64. Because
of the following fix and to help reduce the stack size, let's reduce it
to 16. This seems large enough for a lot of use cases (e.g. sandboxed
init service, spawning a sandboxed SSH service, in nested sandboxed
containers). Reducing the number of nested domains may also help to
discover misuse of Landlock (e.g. creating a domain per rule).
Add and use a dedicated layer_mask_t typedef to fit with the number of
layers. This might be useful when changing it and to keep it consistent
with the maximum number of layers.
Reviewed-by: Paul Moore <paul@paul-moore.com>
Link: https://lore.kernel.org/r/20220506161102.525323-3-mic@digikod.net
Cc: stable@vger.kernel.org
Signed-off-by: Mickaël Salaün <mic@digikod.net>
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| 5f2ff33e | 06-May-2022 |
Mickaël Salaün <mic@digikod.net> |
landlock: Define access_mask_t to enforce a consistent access mask size
Create and use the access_mask_t typedef to enforce a consistent access
mask size and uniformly use a 16-bits type. This will
landlock: Define access_mask_t to enforce a consistent access mask size
Create and use the access_mask_t typedef to enforce a consistent access
mask size and uniformly use a 16-bits type. This will helps transition
to a 32-bits value one day.
Add a build check to make sure all (filesystem) access rights fit in.
This will be extended with a following commit.
Reviewed-by: Paul Moore <paul@paul-moore.com>
Link: https://lore.kernel.org/r/20220506161102.525323-2-mic@digikod.net
Cc: stable@vger.kernel.org
Signed-off-by: Mickaël Salaün <mic@digikod.net>
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| eba39ca4 | 06-May-2022 |
Mickaël Salaün <mic@digikod.net> |
landlock: Change landlock_restrict_self(2) check ordering
According to the Landlock goal to be a security feature available to
unprivileges processes, it makes more sense to first check for
no_new_p
landlock: Change landlock_restrict_self(2) check ordering
According to the Landlock goal to be a security feature available to
unprivileges processes, it makes more sense to first check for
no_new_privs before checking anything else (i.e. syscall arguments).
Merge inval_fd_enforce and unpriv_enforce_without_no_new_privs tests
into the new restrict_self_checks_ordering. This is similar to the
previous commit checking other syscalls.
Link: https://lore.kernel.org/r/20220506160820.524344-10-mic@digikod.net
Cc: stable@vger.kernel.org
Signed-off-by: Mickaël Salaün <mic@digikod.net>
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| 589172e5 | 06-May-2022 |
Mickaël Salaün <mic@digikod.net> |
landlock: Change landlock_add_rule(2) argument check ordering
This makes more sense to first check the ruleset FD and then the rule
attribute. It will be useful to factor out code for other rule ty
landlock: Change landlock_add_rule(2) argument check ordering
This makes more sense to first check the ruleset FD and then the rule
attribute. It will be useful to factor out code for other rule types.
Add inval_add_rule_arguments tests, extension of empty_path_beneath_attr
tests, to also check error ordering for landlock_add_rule(2).
Link: https://lore.kernel.org/r/20220506160820.524344-9-mic@digikod.net
Cc: stable@vger.kernel.org
Signed-off-by: Mickaël Salaün <mic@digikod.net>
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| 06a1c40a | 06-May-2022 |
Mickaël Salaün <mic@digikod.net> |
landlock: Format with clang-format
Let's follow a consistent and documented coding style. Everything may
not be to our liking but it is better than tacit knowledge. Moreover,
this will help mainta
landlock: Format with clang-format
Let's follow a consistent and documented coding style. Everything may
not be to our liking but it is better than tacit knowledge. Moreover,
this will help maintain style consistency between different developers.
This contains only whitespace changes.
Automatically formatted with:
clang-format-14 -i security/landlock/*.[ch] include/uapi/linux/landlock.h
Link: https://lore.kernel.org/r/20220506160513.523257-3-mic@digikod.net
Cc: stable@vger.kernel.org
Signed-off-by: Mickaël Salaün <mic@digikod.net>
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