mirror of https://gitee.com/openkylin/linux.git
94 lines
3.4 KiB
ReStructuredText
94 lines
3.4 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
|
|
|
|
============================
|
|
BPF_PROG_TYPE_CGROUP_SOCKOPT
|
|
============================
|
|
|
|
``BPF_PROG_TYPE_CGROUP_SOCKOPT`` program type can be attached to two
|
|
cgroup hooks:
|
|
|
|
* ``BPF_CGROUP_GETSOCKOPT`` - called every time process executes ``getsockopt``
|
|
system call.
|
|
* ``BPF_CGROUP_SETSOCKOPT`` - called every time process executes ``setsockopt``
|
|
system call.
|
|
|
|
The context (``struct bpf_sockopt``) has associated socket (``sk``) and
|
|
all input arguments: ``level``, ``optname``, ``optval`` and ``optlen``.
|
|
|
|
BPF_CGROUP_SETSOCKOPT
|
|
=====================
|
|
|
|
``BPF_CGROUP_SETSOCKOPT`` is triggered *before* the kernel handling of
|
|
sockopt and it has writable context: it can modify the supplied arguments
|
|
before passing them down to the kernel. This hook has access to the cgroup
|
|
and socket local storage.
|
|
|
|
If BPF program sets ``optlen`` to -1, the control will be returned
|
|
back to the userspace after all other BPF programs in the cgroup
|
|
chain finish (i.e. kernel ``setsockopt`` handling will *not* be executed).
|
|
|
|
Note, that ``optlen`` can not be increased beyond the user-supplied
|
|
value. It can only be decreased or set to -1. Any other value will
|
|
trigger ``EFAULT``.
|
|
|
|
Return Type
|
|
-----------
|
|
|
|
* ``0`` - reject the syscall, ``EPERM`` will be returned to the userspace.
|
|
* ``1`` - success, continue with next BPF program in the cgroup chain.
|
|
|
|
BPF_CGROUP_GETSOCKOPT
|
|
=====================
|
|
|
|
``BPF_CGROUP_GETSOCKOPT`` is triggered *after* the kernel handing of
|
|
sockopt. The BPF hook can observe ``optval``, ``optlen`` and ``retval``
|
|
if it's interested in whatever kernel has returned. BPF hook can override
|
|
the values above, adjust ``optlen`` and reset ``retval`` to 0. If ``optlen``
|
|
has been increased above initial ``getsockopt`` value (i.e. userspace
|
|
buffer is too small), ``EFAULT`` is returned.
|
|
|
|
This hook has access to the cgroup and socket local storage.
|
|
|
|
Note, that the only acceptable value to set to ``retval`` is 0 and the
|
|
original value that the kernel returned. Any other value will trigger
|
|
``EFAULT``.
|
|
|
|
Return Type
|
|
-----------
|
|
|
|
* ``0`` - reject the syscall, ``EPERM`` will be returned to the userspace.
|
|
* ``1`` - success: copy ``optval`` and ``optlen`` to userspace, return
|
|
``retval`` from the syscall (note that this can be overwritten by
|
|
the BPF program from the parent cgroup).
|
|
|
|
Cgroup Inheritance
|
|
==================
|
|
|
|
Suppose, there is the following cgroup hierarchy where each cgroup
|
|
has ``BPF_CGROUP_GETSOCKOPT`` attached at each level with
|
|
``BPF_F_ALLOW_MULTI`` flag::
|
|
|
|
A (root, parent)
|
|
\
|
|
B (child)
|
|
|
|
When the application calls ``getsockopt`` syscall from the cgroup B,
|
|
the programs are executed from the bottom up: B, A. First program
|
|
(B) sees the result of kernel's ``getsockopt``. It can optionally
|
|
adjust ``optval``, ``optlen`` and reset ``retval`` to 0. After that
|
|
control will be passed to the second (A) program which will see the
|
|
same context as B including any potential modifications.
|
|
|
|
Same for ``BPF_CGROUP_SETSOCKOPT``: if the program is attached to
|
|
A and B, the trigger order is B, then A. If B does any changes
|
|
to the input arguments (``level``, ``optname``, ``optval``, ``optlen``),
|
|
then the next program in the chain (A) will see those changes,
|
|
*not* the original input ``setsockopt`` arguments. The potentially
|
|
modified values will be then passed down to the kernel.
|
|
|
|
Example
|
|
=======
|
|
|
|
See ``tools/testing/selftests/bpf/progs/sockopt_sk.c`` for an example
|
|
of BPF program that handles socket options.
|