| Message ID | 20220712211405.14705-5-gnoack3000@gmail.com (mailing list archive) |
|---|---|
| State | Handled Elsewhere |
| Headers | show |
| Series | landlock: truncate support | expand |
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@gmail.com> > Link: https://lore.kernel.org/all/20220707200612.132705-1-gnoack3000@gmail.com/ > --- > 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
On Fri, Jul 29, 2022 at 12:47:46PM +0200, Mickaël Salaün wrote: > > 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@gmail.com> > > Link: https://lore.kernel.org/all/20220707200612.132705-1-gnoack3000@gmail.com/ > > --- > > 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"? Done. > > > > + 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. Done. (Both are mildly confusing, IMHO %-)) > [...] --
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"); + return 1; + } + if (abi < 3) { + ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_TRUNCATE; + } 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. 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
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@gmail.com> Link: https://lore.kernel.org/all/20220707200612.132705-1-gnoack3000@gmail.com/ --- Documentation/userspace-api/landlock.rst | 19 ++++++++++++++----- 1 file changed, 14 insertions(+), 5 deletions(-)