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bpf: Add kconfig knob for disabling unpriv bpf by default

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Add a kconfig knob which allows for unprivileged bpf to be disabled by default.
If set, the knob sets /proc/sys/kernel/unprivileged_bpf_disabled to value of 2.

This still allows a transition of 2 -> {0,1} through an admin. Similarly,
this also still keeps 1 -> {1} behavior intact, so that once set to permanently
disabled, it cannot be undone aside from a reboot.

We've also added extra2 with max of 2 for the procfs handler, so that an admin
still has a chance to toggle between 0 <-> 2.

Either way, as an additional alternative, applications can make use of CAP_BPF
that we added a while ago.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/74ec548079189e4e4dffaeb42b8987bb3c852eee.1620765074.git.daniel@iogearbox.net
This commit is contained in:
Daniel Borkmann 2021-05-11 22:35:17 +02:00 • committed by Alexei Starovoitov
parent b24abcff91
commit 08389d8882
4 changed files with 50 additions and 9 deletions
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17
Documentation/admin-guide/sysctl/kernel.rst
View file

@ -1457,11 +1457,22 @@ unprivileged_bpf_disabled
=========================
Writing 1 to this entry will disable unprivileged calls to ``bpf()``;
once disabled, calling ``bpf()`` without ``CAP_SYS_ADMIN`` will return
``-EPERM``.
once disabled, calling ``bpf()`` without ``CAP_SYS_ADMIN`` or ``CAP_BPF``
will return ``-EPERM``. Once set to 1, this can't be cleared from the
running kernel anymore.
Once set, this can't be cleared.
Writing 2 to this entry will also disable unprivileged calls to ``bpf()``,
however, an admin can still change this setting later on, if needed, by
writing 0 or 1 to this entry.
If ``BPF_UNPRIV_DEFAULT_OFF`` is enabled in the kernel config, then this
entry will default to 2 instead of 0.
= =============================================================
0 Unprivileged calls to ``bpf()`` are enabled
1 Unprivileged calls to ``bpf()`` are disabled without recovery
2 Unprivileged calls to ``bpf()`` are disabled
= =============================================================
watchdog
========