On 12/07/2022 23:14, Günther Noack wrote:
Use the LANDLOCK_ACCESS_FS_TRUNCATE flag in the tutorial.
Adapt the backwards compatibility example and discussion to remove the
truncation flag if needed.
Signed-off-by: Günther Noack <gnoack3000@xxxxxxxxx>
Link: https://lore.kernel.org/all/20220707200612.132705-1-gnoack3000@xxxxxxxxx/
---
Documentation/userspace-api/landlock.rst | 19 ++++++++++++++-----
1 file changed, 14 insertions(+), 5 deletions(-)
diff --git a/Documentation/userspace-api/landlock.rst b/Documentation/userspace-api/landlock.rst
index b86fd94ae797..41fa464cc8b8 100644
--- a/Documentation/userspace-api/landlock.rst
+++ b/Documentation/userspace-api/landlock.rst
@@ -60,7 +60,8 @@ the need to be explicit about the denied-by-default access rights.
LANDLOCK_ACCESS_FS_MAKE_FIFO |
LANDLOCK_ACCESS_FS_MAKE_BLOCK |
LANDLOCK_ACCESS_FS_MAKE_SYM |
- LANDLOCK_ACCESS_FS_REFER,
+ LANDLOCK_ACCESS_FS_REFER |
+ LANDLOCK_ACCESS_FS_TRUNCATE,
};
Because we may not know on which kernel version an application will be
@@ -69,14 +70,22 @@ should try to protect users as much as possible whatever the kernel they are
using. To avoid binary enforcement (i.e. either all security features or
none), we can leverage a dedicated Landlock command to get the current version
of the Landlock ABI and adapt the handled accesses. Let's check if we should
-remove the `LANDLOCK_ACCESS_FS_REFER` access right which is only supported
-starting with the second version of the ABI.
+remove the `LANDLOCK_ACCESS_FS_REFER` and `LANDLOCK_ACCESS_FS_TRUNCATE` access
+rights, which are only supported starting with the second and third version of
+the ABI.
.. code-block:: c
int abi;
abi = landlock_create_ruleset(NULL, 0, LANDLOCK_CREATE_RULESET_VERSION);
+ if (abi == -1) {
+ perror("Landlock is unsupported on this kernel");
"Landlock is not supported with the running kernel"?
+ return 1;
+ }
+ if (abi < 3) {
+ ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_TRUNCATE;
+ }
I guess we could use the same switch/case code as for the sample. I'm
not sure what would be the less confusing for users though.
if (abi < 2) {
ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_REFER;
}
@@ -127,8 +136,8 @@ descriptor.
It may also be required to create rules following the same logic as explained
for the ruleset creation, by filtering access rights according to the Landlock
-ABI version. In this example, this is not required because
-`LANDLOCK_ACCESS_FS_REFER` is not allowed by any rule.
+ABI version. In this example, this is not required because all of the requested
+``allowed_access`` rights are already available in ABI 1.
Good!
We now have a ruleset with one rule allowing read access to ``/usr`` while
denying all other handled accesses for the filesystem. The next step is to
