diff options
Diffstat (limited to 'Documentation/userspace-api')
12 files changed, 263 insertions, 35 deletions
diff --git a/Documentation/userspace-api/ioctl/cdrom.rst b/Documentation/userspace-api/ioctl/cdrom.rst index 682948fc88a3..2ad91dbebd7c 100644 --- a/Documentation/userspace-api/ioctl/cdrom.rst +++ b/Documentation/userspace-api/ioctl/cdrom.rst @@ -718,6 +718,9 @@ CDROMPLAYBLK CDROMGETSPINDOWN + Obsolete, was ide-cd only + + usage:: char spindown; @@ -736,6 +739,9 @@ CDROMGETSPINDOWN CDROMSETSPINDOWN + Obsolete, was ide-cd only + + usage:: char spindown diff --git a/Documentation/userspace-api/landlock.rst b/Documentation/userspace-api/landlock.rst index f35552ff19ba..b8ea59493964 100644 --- a/Documentation/userspace-api/landlock.rst +++ b/Documentation/userspace-api/landlock.rst @@ -1,14 +1,14 @@ .. SPDX-License-Identifier: GPL-2.0 .. Copyright © 2017-2020 Mickaël Salaün <mic@digikod.net> .. Copyright © 2019-2020 ANSSI -.. Copyright © 2021 Microsoft Corporation +.. Copyright © 2021-2022 Microsoft Corporation ===================================== Landlock: unprivileged access control ===================================== :Author: Mickaël Salaün -:Date: March 2021 +:Date: May 2022 The goal of Landlock is to enable to restrict ambient rights (e.g. global filesystem access) for a set of processes. Because Landlock is a stackable @@ -18,6 +18,13 @@ is expected to help mitigate the security impact of bugs or unexpected/malicious behaviors in user space applications. Landlock empowers any process, including unprivileged ones, to securely restrict themselves. +We can quickly make sure that Landlock is enabled in the running system by +looking for "landlock: Up and running" in kernel logs (as root): ``dmesg | grep +landlock || journalctl -kg landlock`` . Developers can also easily check for +Landlock support with a :ref:`related system call <landlock_abi_versions>`. If +Landlock is not currently supported, we need to :ref:`configure the kernel +appropriately <kernel_support>`. + Landlock rules ============== @@ -29,14 +36,15 @@ the thread enforcing it, and its future children. Defining and enforcing a security policy ---------------------------------------- -We first need to create the ruleset that will contain our rules. For this +We first need to define the ruleset that will contain our rules. For this example, the ruleset will contain rules that only allow read actions, but write actions will be denied. The ruleset then needs to handle both of these kind of -actions. +actions. This is required for backward and forward compatibility (i.e. the +kernel and user space may not know each other's supported restrictions), hence +the need to be explicit about the denied-by-default access rights. .. code-block:: c - int ruleset_fd; struct landlock_ruleset_attr ruleset_attr = { .handled_access_fs = LANDLOCK_ACCESS_FS_EXECUTE | @@ -51,9 +59,34 @@ actions. LANDLOCK_ACCESS_FS_MAKE_SOCK | LANDLOCK_ACCESS_FS_MAKE_FIFO | LANDLOCK_ACCESS_FS_MAKE_BLOCK | - LANDLOCK_ACCESS_FS_MAKE_SYM, + LANDLOCK_ACCESS_FS_MAKE_SYM | + LANDLOCK_ACCESS_FS_REFER, }; +Because we may not know on which kernel version an application will be +executed, it is safer to follow a best-effort security approach. Indeed, we +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. + +.. code-block:: c + + int abi; + + abi = landlock_create_ruleset(NULL, 0, LANDLOCK_CREATE_RULESET_VERSION); + if (abi < 2) { + ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_REFER; + } + +This enables to create an inclusive ruleset that will contain our rules. + +.. code-block:: c + + int ruleset_fd; + ruleset_fd = landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0); if (ruleset_fd < 0) { perror("Failed to create a ruleset"); @@ -92,6 +125,11 @@ descriptor. return 1; } +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. + 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 restrict the current thread from gaining more privileges (e.g. thanks to a SUID @@ -125,6 +163,27 @@ ruleset. Full working code can be found in `samples/landlock/sandboxer.c`_. +Good practices +-------------- + +It is recommended setting access rights to file hierarchy leaves as much as +possible. For instance, it is better to be able to have ``~/doc/`` as a +read-only hierarchy and ``~/tmp/`` as a read-write hierarchy, compared to +``~/`` as a read-only hierarchy and ``~/tmp/`` as a read-write hierarchy. +Following this good practice leads to self-sufficient hierarchies that don't +depend on their location (i.e. parent directories). This is particularly +relevant when we want to allow linking or renaming. Indeed, having consistent +access rights per directory enables to change the location of such directory +without relying on the destination directory access rights (except those that +are required for this operation, see `LANDLOCK_ACCESS_FS_REFER` documentation). +Having self-sufficient hierarchies also helps to tighten the required access +rights to the minimal set of data. This also helps avoid sinkhole directories, +i.e. directories where data can be linked to but not linked from. However, +this depends on data organization, which might not be controlled by developers. +In this case, granting read-write access to ``~/tmp/``, instead of write-only +access, would potentially allow to move ``~/tmp/`` to a non-readable directory +and still keep the ability to list the content of ``~/tmp/``. + Layers of file path access rights --------------------------------- @@ -192,6 +251,58 @@ To be allowed to use :manpage:`ptrace(2)` and related syscalls on a target process, a sandboxed process should have a subset of the target process rules, which means the tracee must be in a sub-domain of the tracer. +Compatibility +============= + +Backward and forward compatibility +---------------------------------- + +Landlock is designed to be compatible with past and future versions of the +kernel. This is achieved thanks to the system call attributes and the +associated bitflags, particularly the ruleset's `handled_access_fs`. Making +handled access right explicit enables the kernel and user space to have a clear +contract with each other. This is required to make sure sandboxing will not +get stricter with a system update, which could break applications. + +Developers can subscribe to the `Landlock mailing list +<https://subspace.kernel.org/lists.linux.dev.html>`_ to knowingly update and +test their applications with the latest available features. In the interest of +users, and because they may use different kernel versions, it is strongly +encouraged to follow a best-effort security approach by checking the Landlock +ABI version at runtime and only enforcing the supported features. + +.. _landlock_abi_versions: + +Landlock ABI versions +--------------------- + +The Landlock ABI version can be read with the sys_landlock_create_ruleset() +system call: + +.. code-block:: c + + int abi; + + abi = landlock_create_ruleset(NULL, 0, LANDLOCK_CREATE_RULESET_VERSION); + if (abi < 0) { + switch (errno) { + case ENOSYS: + printf("Landlock is not supported by the current kernel.\n"); + break; + case EOPNOTSUPP: + printf("Landlock is currently disabled.\n"); + break; + } + return 0; + } + if (abi >= 2) { + printf("Landlock supports LANDLOCK_ACCESS_FS_REFER.\n"); + } + +The following kernel interfaces are implicitly supported by the first ABI +version. Features only supported from a specific version are explicitly marked +as such. + Kernel interface ================ @@ -228,21 +339,6 @@ Enforcing a ruleset Current limitations =================== -File renaming and linking -------------------------- - -Because Landlock targets unprivileged access controls, it is needed to properly -handle composition of rules. Such property also implies rules nesting. -Properly handling multiple layers of ruleset, each one of them able to restrict -access to files, also implies to inherit the ruleset restrictions from a parent -to its hierarchy. Because files are identified and restricted by their -hierarchy, moving or linking a file from one directory to another implies to -propagate the hierarchy constraints. To protect against privilege escalations -through renaming or linking, and for the sake of simplicity, Landlock currently -limits linking and renaming to the same directory. Future Landlock evolutions -will enable more flexibility for renaming and linking, with dedicated ruleset -flags. - Filesystem topology modification -------------------------------- @@ -267,8 +363,8 @@ restrict such paths with dedicated ruleset flags. Ruleset layers -------------- -There is a limit of 64 layers of stacked rulesets. This can be an issue for a -task willing to enforce a new ruleset in complement to its 64 inherited +There is a limit of 16 layers of stacked rulesets. This can be an issue for a +task willing to enforce a new ruleset in complement to its 16 inherited rulesets. Once this limit is reached, sys_landlock_restrict_self() returns E2BIG. It is then strongly suggested to carefully build rulesets once in the life of a thread, especially for applications able to launch other applications @@ -281,6 +377,44 @@ Memory usage Kernel memory allocated to create rulesets is accounted and can be restricted by the Documentation/admin-guide/cgroup-v1/memory.rst. +Previous limitations +==================== + +File renaming and linking (ABI 1) +--------------------------------- + +Because Landlock targets unprivileged access controls, it needs to properly +handle composition of rules. Such property also implies rules nesting. +Properly handling multiple layers of rulesets, each one of them able to +restrict access to files, also implies inheritance of the ruleset restrictions +from a parent to its hierarchy. Because files are identified and restricted by +their hierarchy, moving or linking a file from one directory to another implies +propagation of the hierarchy constraints, or restriction of these actions +according to the potentially lost constraints. To protect against privilege +escalations through renaming or linking, and for the sake of simplicity, +Landlock previously limited linking and renaming to the same directory. +Starting with the Landlock ABI version 2, it is now possible to securely +control renaming and linking thanks to the new `LANDLOCK_ACCESS_FS_REFER` +access right. + +.. _kernel_support: + +Kernel support +============== + +Landlock was first introduced in Linux 5.13 but it must be configured at build +time with `CONFIG_SECURITY_LANDLOCK=y`. Landlock must also be enabled at boot +time as the other security modules. The list of security modules enabled by +default is set with `CONFIG_LSM`. The kernel configuration should then +contains `CONFIG_LSM=landlock,[...]` with `[...]` as the list of other +potentially useful security modules for the running system (see the +`CONFIG_LSM` help). + +If the running kernel doesn't have `landlock` in `CONFIG_LSM`, then we can +still enable it by adding ``lsm=landlock,[...]`` to +Documentation/admin-guide/kernel-parameters.rst thanks to the bootloader +configuration. + Questions and answers ===================== diff --git a/Documentation/userspace-api/media/drivers/uvcvideo.rst b/Documentation/userspace-api/media/drivers/uvcvideo.rst index e5fd8fad333c..a290f9fadae9 100644 --- a/Documentation/userspace-api/media/drivers/uvcvideo.rst +++ b/Documentation/userspace-api/media/drivers/uvcvideo.rst @@ -7,7 +7,7 @@ This file documents some driver-specific aspects of the UVC driver, such as driver-specific ioctls and implementation notes. Questions and remarks can be sent to the Linux UVC development mailing list at -linux-uvc-devel@lists.berlios.de. +linux-media@vger.kernel.org. Extension Unit (XU) support diff --git a/Documentation/userspace-api/media/mediactl/media-controller-model.rst b/Documentation/userspace-api/media/mediactl/media-controller-model.rst index 222cb99debb5..78bfdfb2a322 100644 --- a/Documentation/userspace-api/media/mediactl/media-controller-model.rst +++ b/Documentation/userspace-api/media/mediactl/media-controller-model.rst @@ -33,3 +33,9 @@ are: - An **interface link** is a point-to-point bidirectional control connection between a Linux Kernel interface and an entity. + +- An **ancillary link** is a point-to-point connection denoting that two + entities form a single logical unit. For example this could represent the + fact that a particular camera sensor and lens controller form a single + physical module, meaning this lens controller drives the lens for this + camera sensor.
\ No newline at end of file diff --git a/Documentation/userspace-api/media/mediactl/media-types.rst b/Documentation/userspace-api/media/mediactl/media-types.rst index 0a26397bd01d..0ffeece1e0c8 100644 --- a/Documentation/userspace-api/media/mediactl/media-types.rst +++ b/Documentation/userspace-api/media/mediactl/media-types.rst @@ -412,14 +412,21 @@ must be set for every pad. is set by drivers and is read-only for applications. * - ``MEDIA_LNK_FL_LINK_TYPE`` - - This is a bitmask that defines the type of the link. Currently, - two types of links are supported: + - This is a bitmask that defines the type of the link. The following + link types are currently supported: .. _MEDIA-LNK-FL-DATA-LINK: - ``MEDIA_LNK_FL_DATA_LINK`` if the link is between two pads + ``MEDIA_LNK_FL_DATA_LINK`` for links that represent a data connection + between two pads. .. _MEDIA-LNK-FL-INTERFACE-LINK: - ``MEDIA_LNK_FL_INTERFACE_LINK`` if the link is between an - interface and an entity + ``MEDIA_LNK_FL_INTERFACE_LINK`` for links that associate an entity to its + interface. + + .. _MEDIA-LNK-FL-ANCILLARY-LINK: + + ``MEDIA_LNK_FL_ANCILLARY_LINK`` for links that represent a physical + relationship between two entities. The link may or may not be + immutable, so applications must not assume either case. diff --git a/Documentation/userspace-api/media/v4l/dev-decoder.rst b/Documentation/userspace-api/media/v4l/dev-decoder.rst index 3cf2b496f2d0..675bc2c3c6b8 100644 --- a/Documentation/userspace-api/media/v4l/dev-decoder.rst +++ b/Documentation/userspace-api/media/v4l/dev-decoder.rst @@ -72,6 +72,12 @@ coded resolution coded width width for given coded resolution. +coding tree unit + processing unit of the HEVC codec (corresponds to macroblock units in + H.264, VP8, VP9), + can use block structures of up to 64×64 pixels. + Good at sub-partitioning the picture into variable sized structures. + decode order the order in which frames are decoded; may differ from display order if the coded format includes a feature of frame reordering; for decoders, @@ -104,7 +110,8 @@ keyframe macroblock a processing unit in image and video compression formats based on linear block transforms (e.g. H.264, VP8, VP9); codec-specific, but for most of - popular codecs the size is 16x16 samples (pixels). + popular codecs the size is 16x16 samples (pixels). The HEVC codec uses a + slightly more flexible processing unit called coding tree unit (CTU). OUTPUT the source buffer queue; for decoders, the queue of buffers containing diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-codec-stateless.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-codec-stateless.rst index 6541e4c32b26..bee73065e993 100644 --- a/Documentation/userspace-api/media/v4l/ext-ctrls-codec-stateless.rst +++ b/Documentation/userspace-api/media/v4l/ext-ctrls-codec-stateless.rst @@ -649,10 +649,16 @@ Stateless Codec Control ID :c:type:`timeval` in struct :c:type:`v4l2_buffer` to a __u64. * - __u32 - ``pic_num`` - - + - For short term references, this must match the derived value PicNum + (8-28) and for long term references it must match the derived value + LongTermPicNum (8-29). When decoding frames (as opposed to fields) + pic_num is the same as FrameNumWrap. * - __u16 - ``frame_num`` - - + - For short term references, this must match the frame_num value from + the slice header syntax (the driver will wrap the value if needed). For + long term references, this must be set to the value of + long_term_frame_idx described in the dec_ref_pic_marking() syntax. * - __u8 - ``fields`` - Specifies how the DPB entry is referenced. See :ref:`Reference Fields <h264_ref_fields>` diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst index 4cd7c541fc30..6183f43f4d73 100644 --- a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst +++ b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst @@ -1180,6 +1180,28 @@ enum v4l2_mpeg_video_h264_entropy_mode - is set to non zero value. Applicable to H264, H263 and MPEG4 encoder. +``V4L2_CID_MPEG_VIDEO_INTRA_REFRESH_PERIOD_TYPE (enum)`` + +enum v4l2_mpeg_video_intra_refresh_period_type - + Sets the type of intra refresh. The period to refresh + the whole frame is specified by V4L2_CID_MPEG_VIDEO_INTRA_REFRESH_PERIOD. + Note that if this control is not present, then it is undefined what + refresh type is used and it is up to the driver to decide. + Applicable to H264 and HEVC encoders. Possible values are: + +.. tabularcolumns:: |p{9.6cm}|p{7.9cm}| + +.. flat-table:: + :header-rows: 0 + :stub-columns: 0 + + * - ``V4L2_MPEG_VIDEO_INTRA_REFRESH_PERIOD_TYPE_RANDOM`` + - The whole frame is completely refreshed randomly + after the specified period. + * - ``V4L2_MPEG_VIDEO_INTRA_REFRESH_PERIOD_TYPE_CYCLIC`` + - The whole frame MBs are completely refreshed in cyclic order + after the specified period. + ``V4L2_CID_MPEG_VIDEO_INTRA_REFRESH_PERIOD (integer)`` Intra macroblock refresh period. This sets the period to refresh the whole frame. In other words, this defines the number of frames diff --git a/Documentation/userspace-api/media/v4l/pixfmt-reserved.rst b/Documentation/userspace-api/media/v4l/pixfmt-reserved.rst index cabfa34b7db5..0ff68cd8cf62 100644 --- a/Documentation/userspace-api/media/v4l/pixfmt-reserved.rst +++ b/Documentation/userspace-api/media/v4l/pixfmt-reserved.rst @@ -239,6 +239,25 @@ please make a proposal on the linux-media mailing list. It remains an opaque intermediate format and the MDP hardware must be used to convert ``V4L2_PIX_FMT_MT21C`` to ``V4L2_PIX_FMT_NV12M``, ``V4L2_PIX_FMT_YUV420M`` or ``V4L2_PIX_FMT_YVU420``. + * .. _V4L2-PIX-FMT-QC08C: + + - ``V4L2_PIX_FMT_QC08C`` + - 'QC08C' + - Compressed Macro-tile 8-Bit YUV420 format used by Qualcomm platforms. + It is an opaque intermediate format. The used compression is lossless + and it is used by various multimedia hardware blocks like GPU, display + controllers, ISP and video accelerators. + It contains four planes for progressive video and eight planes for + interlaced video. + * .. _V4L2-PIX-FMT-QC10C: + + - ``V4L2_PIX_FMT_QC10C`` + - 'QC10C' + - Compressed Macro-tile 10-Bit YUV420 format used by Qualcomm platforms. + It is an opaque intermediate format. The used compression is lossless + and it is used by various multimedia hardware blocks like GPU, display + controllers, ISP and video accelerators. + It contains four planes for progressive video. .. raw:: latex \normalsize diff --git a/Documentation/userspace-api/media/v4l/pixfmt-yuv-luma.rst b/Documentation/userspace-api/media/v4l/pixfmt-yuv-luma.rst index 8ebd58c3588f..6a387f9df3ba 100644 --- a/Documentation/userspace-api/media/v4l/pixfmt-yuv-luma.rst +++ b/Documentation/userspace-api/media/v4l/pixfmt-yuv-luma.rst @@ -48,6 +48,17 @@ are often referred to as greyscale formats. - ... - ... + * .. _V4L2-PIX-FMT-IPU3-Y10: + + - ``V4L2_PIX_FMT_IPU3_Y10`` + - 'ip3y' + + - Y'\ :sub:`0`\ [7:0] + - Y'\ :sub:`1`\ [5:0] Y'\ :sub:`0`\ [9:8] + - Y'\ :sub:`2`\ [3:0] Y'\ :sub:`1`\ [9:6] + - Y'\ :sub:`3`\ [1:0] Y'\ :sub:`2`\ [9:4] + - Y'\ :sub:`3`\ [9:2] + * .. _V4L2-PIX-FMT-Y10: - ``V4L2_PIX_FMT_Y10`` @@ -133,4 +144,5 @@ are often referred to as greyscale formats. For the Y16 and Y16_BE formats, the actual sampling precision may be lower than 16 bits. For example, 10 bits per pixel uses values in the range 0 to - 1023. + 1023. For the IPU3_Y10 format 25 pixels are packed into 32 bytes, which + leaves the 6 most significant bits of the last byte padded with 0. diff --git a/Documentation/userspace-api/media/v4l/vidioc-streamon.rst b/Documentation/userspace-api/media/v4l/vidioc-streamon.rst index 0bc86f06947b..1a79313a29fa 100644 --- a/Documentation/userspace-api/media/v4l/vidioc-streamon.rst +++ b/Documentation/userspace-api/media/v4l/vidioc-streamon.rst @@ -43,8 +43,7 @@ the capture or output process during streaming Capture hardware is disabled and no input buffers are filled (if there are any empty buffers in the incoming queue) until ``VIDIOC_STREAMON`` has been called. Output hardware is disabled and no video signal is -produced until ``VIDIOC_STREAMON`` has been called. The ioctl will -succeed when at least one output buffer is in the incoming queue. +produced until ``VIDIOC_STREAMON`` has been called. Memory-to-memory devices will not start until ``VIDIOC_STREAMON`` has been called for both the capture and output stream types. diff --git a/Documentation/userspace-api/seccomp_filter.rst b/Documentation/userspace-api/seccomp_filter.rst index 539e9d4a4860..d1e2b9193f09 100644 --- a/Documentation/userspace-api/seccomp_filter.rst +++ b/Documentation/userspace-api/seccomp_filter.rst @@ -271,6 +271,16 @@ notifying process it will be replaced. The supervisor can also add an FD, and respond atomically by using the ``SECCOMP_ADDFD_FLAG_SEND`` flag and the return value will be the injected file descriptor number. +The notifying process can be preempted, resulting in the notification being +aborted. This can be problematic when trying to take actions on behalf of the +notifying process that are long-running and typically retryable (mounting a +filesytem). Alternatively, at filter installation time, the +``SECCOMP_FILTER_FLAG_WAIT_KILLABLE_RECV`` flag can be set. This flag makes it +such that when a user notification is received by the supervisor, the notifying +process will ignore non-fatal signals until the response is sent. Signals that +are sent prior to the notification being received by userspace are handled +normally. + It is worth noting that ``struct seccomp_data`` contains the values of register arguments to the syscall, but does not contain pointers to memory. The task's memory is accessible to suitably privileged traces via ``ptrace()`` or |