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author | Stanislav Fomichev <sdf@google.com> | 2020-06-17 03:04:16 +0200 |
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committer | Alexei Starovoitov <ast@kernel.org> | 2020-06-17 19:54:05 +0200 |
commit | 8030e250d882db174cbcd88273570ffb36a13080 (patch) | |
tree | dc7cd3c1ae17b73b2a7e56cef6eaac706ae3c080 /Documentation/bpf | |
parent | selftests/bpf: Make sure optvals > PAGE_SIZE are bypassed (diff) | |
download | linux-8030e250d882db174cbcd88273570ffb36a13080.tar.xz linux-8030e250d882db174cbcd88273570ffb36a13080.zip |
bpf: Document optval > PAGE_SIZE behavior for sockopt hooks
Extend existing doc with more details about requiring ctx->optlen = 0
for handling optval > PAGE_SIZE.
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200617010416.93086-3-sdf@google.com
Diffstat (limited to 'Documentation/bpf')
-rw-r--r-- | Documentation/bpf/prog_cgroup_sockopt.rst | 14 |
1 files changed, 14 insertions, 0 deletions
diff --git a/Documentation/bpf/prog_cgroup_sockopt.rst b/Documentation/bpf/prog_cgroup_sockopt.rst index c47d974629ae..172f957204bf 100644 --- a/Documentation/bpf/prog_cgroup_sockopt.rst +++ b/Documentation/bpf/prog_cgroup_sockopt.rst @@ -86,6 +86,20 @@ 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. +Large optval +============ +When the ``optval`` is greater than the ``PAGE_SIZE``, the BPF program +can access only the first ``PAGE_SIZE`` of that data. So it has to options: + +* Set ``optlen`` to zero, which indicates that the kernel should + use the original buffer from the userspace. Any modifications + done by the BPF program to the ``optval`` are ignored. +* Set ``optlen`` to the value less than ``PAGE_SIZE``, which + indicates that the kernel should use BPF's trimmed ``optval``. + +When the BPF program returns with the ``optlen`` greater than +``PAGE_SIZE``, the userspace will receive ``EFAULT`` errno. + Example ======= |