Commit eb33f2cc authored Nov 22, 2017 by Gianluca Borello Committed by Daniel Borkmann Nov 22, 2017

bpf: remove explicit handling of 0 for arg2 in bpf_probe_read

Commit 9c019e2b ("bpf: change helper bpf_probe_read arg2 type to
ARG_CONST_SIZE_OR_ZERO") changed arg2 type to ARG_CONST_SIZE_OR_ZERO to
simplify writing bpf programs by taking advantage of the new semantics
introduced for ARG_CONST_SIZE_OR_ZERO which allows <!NULL, 0> arguments.

In order to prevent the helper from actually passing a NULL pointer to
probe_kernel_read, which can happen when <NULL, 0> is passed to the helper,
the commit also introduced an explicit check against size == 0.

After the recent introduction of the ARG_PTR_TO_MEM_OR_NULL type,
bpf_probe_read can not receive a pair of <NULL, 0> arguments anymore, thus
the check is not needed anymore and can be removed, since probe_kernel_read
can correctly handle a <!NULL, 0> call. This also fixes the semantics of
the helper before it gets officially released and bpf programs start
relying on this check.

Fixes: 9c019e2b ("bpf: change helper bpf_probe_read arg2 type to ARG_CONST_SIZE_OR_ZERO")
Signed-off-by: Gianluca Borello <g.borello@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

parent db1ac496

kernel/trace/bpf_trace.c

+1 −5

Original line number	Diff line number	Diff line
		@@ -78,16 +78,12 @@ EXPORT_SYMBOL_GPL(trace_call_bpf);

		BPF_CALL_3(bpf_probe_read, void , dst, u32, size, const void , unsafe_ptr)
		{
		int ret = 0;

		if (unlikely(size == 0))
		goto out;
		int ret;

		ret = probe_kernel_read(dst, unsafe_ptr, size);
		if (unlikely(ret < 0))
		memset(dst, 0, size);

		out:
		return ret;
		}

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